The Geometry of Vision and the Mind-Body Problem 0820403881

Citation preview

American University Studies

Robert E. French

The Geometry of Vision and the Mind Body Problem

■

j

Peter Lang

The Geometry of Vision and the Mind Body Problem

■

The Geometry of Vision and the Mind Body Problem

American University Studies

Series V Philosophy Vol. 24

PETER LANG New York • Bern • Frankfurt am Main • Paris

Robert E. French

The Geometry of Vision and the Mind Body Problem

PETER LANG New York • Bern • Frankfurt am Main • Paris

Library of Congress Cataloging-in-Publication Data French, Robert E. The geometry of vision and the mind body problem.

(American university studies. Series V, Philosophy ; vol. 24) Bibliography: p. I. Space perception. 2. Visual perception. 3. Mind and body. I. Title. II. Series: American university studies. Series V, Philosophy ; v.24. BF469.F74 1987 128.3 86-27684 ISBN 0-8204-0388-1 ISSN 0-0739-6392

CIP-Kurztitclaufnahme det Dcutschen Bibliothek

French, Robert E.: The geometry of vision and the mind body problem / Robert E. French. - New York: Bern; Frankfurt am Main; Paris: Lang, 1987. (American University Studies: Ser. 5, Philosophy; Vol. 24) ISBN 0-8204-0388-1

NE: American University Studies / 09

© Peter Lang Publishing, Inc., New York 1987

All rights reserved. Reprint or reproduction, even partially, in all forms such as microfilm, xerography, microfiche, microcard, offset strictly prohibited.

Printed by Weihert-Druck GmbH, Darmstadt, West Germany

ACKNOWLEDGMENTS

Among the people whom I would like to thank for help in writing this book and in its production are Judson Webb and Abner Shimony of Boston University, Steven Pinker and Sean True of M.I.T., Tim Schermer and John Chinlund of Augustana College, Fred Adams of Central Michigan University, Tyler Lorrig of Yale, my brother John, my wife Mary, and my parents, Rowland and Winifred French.

5

1

TABLE OF CONTENTS Introduction

1

A Refutation of Naive Realism The Non-productiveness of Naive Realism as a Theory of Perception 1.2 The Causal Theory of Perception 1.3 Language and Perception 1.4 The Attitudinal Shift to Visual Space 1.5 The Legitimacy of Introspective Evidence

3

1. 1.1

2. 2.1 2.2 2.3 2.4 2.5

The Topology of Visual Space The Continuity of Visual Space The Boundedness of Visual Space An Analysis of “Dimension” The Dimensionality of Visual Space An Analysis of Visual Depth Perception

The Metric Structure of Visual Space Evidence that Visual Space Possesses a Euclidean Metric 3.2 Evidence that Visual Space Possesses a Spherical Metric 3.3 Evidence that Visual Space Possesses a Hyperbolic Metric 3.4 Evidence that Visual Space Possesses a Variable Curvature 3. 3.1

5 10 19 29 32 37 39 45 46 51 57 73 77 83

93

106

4.

Visual Orientation, Phenomenal Space, Regresses, and Outness 4.1 Visual Orientation 4.2 The Geometry of Phenomenal Space 4.3 The Eye Regress 4.4 Outness and the “Self’

117 119 123 131 137

5. 5.1 5.2 5.3 5.4

The Mind Body Problem Constraints on Mind Body Causal Connections The Neurophysiology of Visual Perception Potential Sites for Mind Body Causal Connections Dualistic Versus Dual Aspect Theories

141 143 151 162 170

Footnotes

175

Bibliography

185

INTRODUCTION In this book I shall both analyze the geometric structure of phenomenal visual space and also investigate the bearing of that structure upon the classic mind body problem, of how there can be a causal connection between the phenomenal and physical realms. By “visual space” I refer to what is immediately presented to us visually, and thus the book can be thought of as presenting a phenomenology of vision from a geometrical point of view. The five chapters in the book are logically connected, in the sense that even while the content of each successive chapter is not logically entailed by the results of the preceding one, nevertheless each one both logically depends upon, and also builds on, earlier results. For example, Chapters Two through Five presuppose the causal theory of perception which is argued for in Chapter One, anc Chapter Three, on the metric structure of visual space, presuppose the two-dimensional topology of that space which is argued for i Chapter Two. Also, I might note that while certain sections of th work involve a fair amount of mathematical sophistication, notably the section deriving the internal metric structure of visual space, in general this is not the case, and in fact an “intuitive” use is made of mathematical concepts which also possess a more technical use. I attempt to point out when such non-standard uses are involved though. Chapter One, in which I distinguish visual space from physical space by means of a refutation of naive realism, should perhaps be unnecessary at this point in time. However, while many of its conclusions may seem to be obvious, I have seen enough confusion on this subject in recent works in both philosophy and psychology that I thought it wise to include it. Also, if later conclusions related to this subject may seem, prima facie, to be somewhat unreasonable or odd, readers can be referred back to arguments in that chapter. In my subsequent two chapters, I proceed to analyze respectively the topology and the metric structure of visual space. My chapter on topology includes in-depth analyses of the continuity and dimension-

2 ality of visual space, while my chapter on the metric structure of visual space deals with such questions as what presuppositions are entailed in assigning a metric structure to a space, and whether the metric structure of visual space is Euclidean or not. Most of my arguments are in these chapters should be relatively straight­ forward, even though the eventual conclusion, that visual space possesses a variable curvature, is novel. Chapter Four contains a mixture of subjects including an analysis of visual orientation, an extension of my treatment of phenomenal geometry to the other senses besides vision, and an investigation into certain regress paradoxes which are sometimes held to apply to the causal theory of perception. Chapter Five is by far the most controversial chapter of the book, dealing with my positive solution to the mind body problem, but I feel that it is about time that the issues involved here are squarely faced. Even if my eventual solution to the problem is not accepted, the analysis leading up to that solution should still at least be thought-provoking. Thus, my first and final chapters will be concerned with the :onnections of visual perception to the mind body problem, while the niddle three chapters will be concerned with geometric phenome­ nology. There are of course many subjects concerning perception which are not covered in depth in the book, notably epistemological issues of how we learn about the nature of the physical world through our perceptions of it, the role of learning in perception, and the precise physiology of the various sense organs, such as the eye. These subject matters are well-covered in other places though, and so I concentrate instead on areas in the philosophy of perception where I feel that there is still conceptual confusion.

CHAPTER ONE A REFUTATION OF NAIVE REALISM There is no greater impediment to the advancement of knowl­ edge than the ambiguity of words. Thomas Reid

The primary subject matter of this book is the geometry of visual space and the implications of that geometry on possible solutions to the mind body problem. However, inasmuch as there has been a certain controversy over the very existence of visual space, it would seem to be prudent to begin the book by investigating the nature of this controversy in some detail. It is pointless to attempt to define “visual space” directly, although various synonyms can be given for the contents of the immediate sensual experience which includes visual space, such as “sensations,” “sense data,” “percepts,” “qualia,” “the given,” “appearances,” “phenomenal experiences,” and “sense experiences” (I shall use these phrases interchangeably ii what follows). Instead, inasmuch as our immediate visual expe rience of the physical world is often taken for at least the frontal surfaces of objects in that world itself, it will turn out that much depends upon the demonstration that these two are in fact always at least numerically distinct. The philosophical position which equates immediate visual expe­ rience with at least the frontal surfaces of the physical objects being viewed, and which also holds that these physical objects continue to exist, in the same format, when they are no longer being perceived, is variously known as “naive realism” or “direct realism.” It can be seen that this position coincides with our common sense attitude towards visual perception. Since recently “direct realism” has sometimes been also used to refer to the position that in visual perception information is held invariant between the object seen and the perceiver while the two are nevertheless numerically dis­ tinct,1 I shall refer to the first position as “naive realism” from here on in spite of its somewhat prejudicial title.

2 ality of visual space, while my chapter on the metric structure of visual space deals with such questions as what presuppositions are entailed in assigning a metric structure to a space, and whether the metric structure of visual space is Euclidean or not. Most of my arguments are in these chapters should be relatively straight­ forward, even though the eventual conclusion, that visual space possesses a variable curvature, is novel. Chapter Four contains a mixture of subjects including an analysis of visual orientation, an extension of my treatment of phenomenal geometry to the other senses besides vision, and an investigation into certain regress paradoxes which are sometimes held to apply to the causal theory of perception. Chapter Five is by far the most controversial chapter of the book, dealing with my positive solution to the mind body problem, but I feel that it is about time that the issues involved here are squarely faced. Even if my eventual solution to the problem is not accepted, the analysis leading up to that solution should still at least be thought-provoking. Thus, my first and final chapters will be concerned with the jonnections of visual perception to the mind body problem, while the middle three chapters will be concerned with geometric phenome­ nology. There are of course many subjects concerning perception which are not covered in depth in the book, notably epistemological issues of how we learn about the nature of the physical world through our perceptions of it, the role of learning in perception, and the precise physiology of the various sense organs, such as the eye. These subject matters are well-covered in other places though, and so I concentrate instead on areas in the philosophy of perception where I feel that there is still conceptual confusion.

CHAPTER ONE A REFUTATION OF NAIVE REALISM There is no greater impediment to the advancement of knowl­ edge than the ambiguity of words. Thomas Reid

The primary subject matter of this book is the geometry of visual space and the implications of that geometry on possible solutions to the mind body problem. However, inasmuch as there has been a certain controversy over the very existence of visual space, it would seem to be prudent to begin the book by investigating the nature of this controversy in some detail. It is pointless to attempt to define “visual space” directly, although various synonyms can be given for the contents of the immediate sensual experience which includes visual space, such as “sensations,” “sense data,” “percepts,” “qualia,” “the given,” “appearances,” “phenomenal experiences,” and “sense experiences” (I shall use these phrases interchangeably in what follows). Instead, inasmuch as our immediate visual expe rience of the physical world is often taken for at least the fronta surfaces of objects in that world itself, it will turn out that much depends upon the demonstration that these two are in fact always at least numerically distinct. The philosophical position which equates immediate visual expe­ rience with at least the frontal surfaces of the physical objects being viewed, and which also holds that these physical objects continue to exist, in the same format, when they are no longer being perceived, is variously known as “naive realism” or “direct realism.” It can be seen that this position coincides with our common sense attitude towards visual perception. Since recently “direct realism” has sometimes been also used to refer to the position that in visual perception information is held invariant between the object seen and the perceiver while the two are nevertheless numerically dis­ tinct,! I shall refer to the first position as “naive realism” from here on in spite of its somewhat prejudicial title.

4

In this chapter I will argue that naive realism, as a theory of visual perception, is non-productive, in the sense that it does not help to elucidate the nature of the visual perception process. I will instead argue that what are taken as being the frontal surfaces of physical objects under the attitude of naive realism are not really parts of physical objects at all, but instead are mental in character (sensory fields), and this book will be concerned with characterizing the geometric character of these sensory fields. This does not mean that naive realism is either inconsistent or refutable by means of citing any particular empirical counterexamples to it, since, as I will point out later, it is always possible to hold onto the theory by making certain verbal moves, such as by claiming that we directly perceive physical objects only in certain manners, such as by directly observing only certain aspects of them, or by perceiving them in the past. However, I will argue that physical objects, as construed by the physical sciences, are very different things from what naive realism takes them to be, and I will also argue that at best they are only “indirectly” perceived, in the sense that our visual ;xperiences of such physical objects are always at least numerically listinct from the objects themselves. I shall begin the chapter with a section showing the defects of naive realism, as a theory of perception. I will point out here numer­ ous asymmetries between the nature of our visual experiences and the nature of the physical world, as described by modern physics. This will be followed by a section elucidating an alternative theory of perception, the causal theory of perception, wherein I will offer an analysis of causation applicable to physical “causal chains,” and will show how such a theory can explain the existence of geometric invariants between macroscopic spatial properties of physical objects and our visual experiences of them. My next section will be devoted to an analysis of perceptual language and the rational reconstructions of it which are necessary for adequately stating the causal theory of perception. I will then finish the chapter with a section on the attitudinal shift away from naive realism which is required in order to analyze the geometry of phenomenal visual space in and of itself, and a section devoted to a defense of the methodology behind my subsequent analysis, which will be based on introspective evidence.

5 1.1 The Non-productiveness of Naive Realism as a Theory of Perception In this section I shall show that naive realism, as a theory of the nature of perception, is non-productive, both in the sense that it does not help to explain why we have the sense experiences we have, and also in the sense that it mistakenly assumes that the world as we experience it is numerically the same as the world studied by the physical sciences. I will begin the section by giving an ostensive definition of our perceptual experiences, and will then move on to to show that the physical world described by modern physics is an extremely different world than the world as we visually perceive it. Some philosophers, notably John Austin2, have held that there is a difficulty in introducing sensory fields, or using the various syn­ onyms for their contents mentioned in my introduction to this chap­ ter, since ordinary English either does not make use of the expres­ sions at all, or else uses them to refer to something else which is not mental in character, such as, for example, when one is expressing: a tentative opinion about what it is that one is seeing or when one is unsure as to how to describe it. I wish to show now that in spite of this “theory-ladenness” (in the sense of assuming the truth of naive realism) of ordinary perceptual language, it is still possible to give at least an ostensive definition of sensory fields, and hence also of the various synonyms for their contents previously mentioned. A partial ostensive definition of sensory fields was implicitly given in my definition of naive realism, and is that at least portions of the fields are numerically identical with what are normally taken to be the frontal surfaces of objects when we are looking at them. This definition is incomplete since sensory fields also include our perceptions of such physical phenomena (albeit not physical objects) as rainbows, flames, and shadows, and also cases of nonveridical “perception” as occur in dreams, hallucinations, and men­ tal imagery. An ostensive definition of the former class would be that portions of the fields are numerically identical with what we ordinarily take to be these physical phenomena as we see them, while an ostensive definition of the latter class would be that por­ tions of the fields are numerically identical with the contents of the dreams and other phenomena referred to. The complete sensory fields would then correspond to the amalgamation of each of these portions. Thus, it follows that, even with just using ordinary Eng-

6 lish, we have words to refer to at least portions of our sensory fields; it is just the case that at least for the portions corresponding to veridical perception, the portions are not ordinarily interpreted as being mental. I shall now turn to my demonstration that naive realism, as a theory of perception, is non-productive by pointing out various asymmetries between properties of physical objects, as they are described by modern physics, and the way in which the objects are perceived. For the time being, I will leave the question open as to whether this perception is “direct” or “indirect.” The general idea behind my strategy here was succinctly put forward by Bertrand Russell in the following much quoted passage from his An Inquiry into Meaning and Truth.

We all start from “naive realism,” i. e. the doctrine that things are what they seem. We think that grass is green, that stones are hard, and that snow is cold. But physics assures us that the greenness of grass, the hardness of stones, and the coldness of snow, are not the greenness, hardness and coldness that we know in our experience, but something very different. The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself. Thus science seems to be a war with itself; when it most means to be objective, it finds itself plunged into subjectivity againstits will. Naive realism leads to physics, and physics, if true, shows that naive realism is false. Therefore naive realism, if true, is false; therefore it is false, (pp. 14,15) Thus, Russell argues that naive realism is a self-defeating posi­ tion inasmuch as it leads to physics, and since the entities postu­ lated by physics are never at least numerically identical with our percepts, whereas common sense mistakenly assumed that they would be. It is important to note that Russell is assuming the truth of physical realism here; i. e., that the atoms and various subatomic particles postulated by modern physics exist independent!}' of our observations of them. There are two important potential problems which must be dealt with in this regard; one being an epistemologi­ cal problem of how we could know about the nature of entities which completely transcend our sense experiences (i. e., which are at best only “indirectly” observed”) and the second being how to account for certain alleged paradoxes associated with physical realism,

7

these being the paradoxes of a realist interpretation of quantum mechanics. I shall deal with the epistemological problem first, and will then sketchily discuss the paradoxes of quantum mechanics. In my following two sections I will cite numerous examples, drawn from both the physical sciences and perceptual psychology, illus­ trating Russell’s basic point that the world postulated by modern physics is a very different world from the one which we are imme­ diately acquainted with in our sense experience. With regard to the epistemological question as to how we deve­ loped the atomic theory (the basic entities postulated by which both completely transcending our immediate sense experiences and being extremely unlike anything which is ever immediately expe­ rienced), even though we only ever immediately experience our sen­ sory fields, it should first be emphasized that in no way did the atomic theory arise out of a simple generalization from sense expe­ rience. Instead, it originated with the ancient Greek atomists (Leu­ cippus and Democritus) by means of a creative act of the imagina­ tion, and it was subsequently refined and tested by means of the hypothetico-deductive form of scientific method,3 until the final modern atomic theory associated with quantum mechanics was developed in the twentieth century. It is worth noting that the mod­ ern atomic theory here differs in many significant ways from the original theory, since, for example, atoms are no longer conceived as being either solid or indestructable. Still, none of the entities postu lated to exist by either version of the theory have ever beer “directly” observed, although it has been possible to make empirical predictions from the theories, and it is from the confirmations and disconfirmations of these empirical predictions that the theories have been tested and refined. Ido not wish to be at all dogmatic here on the “chicken and egg” question, as to whether theories or obser­ vations must always come first in the hypothetico-deductive method, since both build dialectically on each other, and since in the case of accidental discoveries, observations may precede a certain phase of a theory. Nevertheless, it remains the case that the atomic theory, in its core tenets, completely transcends our sense expe­ riences. I now wish very briefly and sketchily to discuss a group of para­ doxes which it is sometimes alleged afflict realist interpretations of quantum mechanics. These include the points that quantum mechan­ ics characterizes quantum events as occurring stochastically and

8 hence as being at least not completely causally determined, the Heisenberg uncertainty principles that an electron’s position and momentum, or energy and time of switching quantum states, can­ not be both given precise values simultaneously, and the paradox of “Schrodinger’s cat” of explaining at what point the probabilistic wave equation governing electron states is “reduced” in the sense of giving definite values to properties of the electron. In spite of these paradoxes, the quantum mechanical algorithms have been extreme­ ly fruitful in giving accurate predictions concerning the outcomes of experiments on the microscopic atomic realm. While admittedly there has been a controversy as to whether a realist interpretation of quantum mechanics is possible at all (with some physicists, notably WigneH and Von Neumann,5 trying to reduce the subject to our perceptual observations), I still wish to opt for a realist account here, if for no other reason than its explanatory power in answering the “why question” as to why our sense experiences are ordered the way that they are. I am not going to discuss the details of realist accounts of quantum mechanics here, such as those given by hidden variable theories, but instead will merely refer readers to the work of physi­ cists who have worked in this area, such as Bohm.6 In any event, even though phenomenalism (the position that physical objects are just logical constructs out of sense experiences) and naiye realism may be logically consistent positions, I still find them both to be deficient in explaining what is responsible for arranging our sense experiences the way they are. Thus, assuming a realist account of the atomic realm, it should be obvious that at least on a microscopic level there is very little in common between the structure of our visual experience and that realm. While it is true that the atomic realm can be at least mathem­ atically modelled, to some extent, with quantum mechanics, it would seem to be very difficult to “picture” that model due to the paradoxes just mentioned, notably those associated with Heisen­ berg’s uncertainty principles. Also, electrons are treated as “point particles” in quantum mechanics and they would not be amenable to visual picturing because of this feature as well. However, the foregoing points do not show that there cannot be macroscopic invariants between our visual experiences of physical objects and the objects themselves, and in fact in my next section, on the causal theory of perception, I will argue for the existence of such invar­ iants. Of course, this is consistent with the two realms being numer-

9 ically distinct though. Thus, I would like to turn now to a detailed discussion of an alternative perceptual theory to phenomenalism and naive realism, the causal theory of perception, and show how that theory is much more productive in explaining the origins of our sense experiences than either of the former two theories.

10 1.2 The Causal Theory of Perception

By the causal theory of perception, I refer to the position holding that it is both the case that the nature of our sense experiences is determined by means of certain physical causal chains in our envir­ onment, and also that in at least visual perception, certain macros­ copic features of that environment are structurally mirrored in the experiences, in this case due to the optics of image formation, and invariances from this optical projection carried into the central nervous system. In order to elucidate the nature of the theory, I will first develop a sense of “causation” which is applicable to physical causal chains, and will then discuss the various structural proper­ ties which are invariant between physical objects being perceived and our visual perceptions of them. The sense of “causality” which I wish to analyze here is one applicable to physical causal chains, such as the light rays connect­ ing physical objects being perceived and our retinal images of those objects. I will analyze this sense of “causality” in terms of “physical lecessity,” or if quantum mechanics is truly probabilistic, in terms if “physical probability.” By “physical necessity,” I refer to the type of necessity by which a physical state of affairs logically and tem­ porally (I add the temporal condition here to distinguish causes from their effects, and while more sophisticated analyses'? may be possible which allow for the coherency of backwards causation, I will not go into them here) follows from a set of physical initial conditions; i. e., another physical state of affairs such as a given configuration of certain atoms in specified states, and the laws of physics (as they really are through “God’s eyes” and not necessarily as we currently know them). The physical state of affairs which logically and temporally follows from applying these laws of phys­ ics to the given initial conditions is then termed to be “physically necessary.” If the laws of quantum mechanics are indeed probabi­ listic, as maintained by current quantum mechanics, then the resulting state of affairs would be merely physically probable. In any event though, my analysis of causation would be that if a state of affairs logically and temporally follows from a set of initial phys­ ical conditions with either necessity or probability according to the laws of physics, then the given initial conditions will be the cause of that state of affairs. It is easy to see how a physical causal chain could be built up in accordance with such an analysis, by seeing

11

what state of affairs is temporally immediately determined by the state of affairs immediat ly determined by the initial conditions and so on. Each new state of affairs would thus possess a cause, and therefore be determined, with at least probability, by physical states of affairs stretching indefinitely far back in the past. It can be inquired as to what type of necessity is involved in “physical necessity.” Is it an anthropormorphic idea which is being extended into non-human and thus inappropriate subject matters as Collingwoods argues is the case with Newton’s conception of a force, or is it, as Hume9 would presumably have argued had he been a materialist, the case that all that is involved is a succession of physical states (instead of sense data states) to which the mind has invoked a type of compulsion? I do not wish to be dogmatic on this issue, although it seems clear to me that there is more involved here than just a Humean type of regular succession of physical states. My primary reason for holding this is the complete poverty of such a position in explaining why the succession of physical states is the way it is. What is responsible for the order which is so precisely described by the laws of physics? It should be noted that the foregoing analysis of causation does not always square very well with the ordinary English usage of the term, since often in ordinary English by a “cause” we are referring to the initiation of a physical causal chain, as in the case of flicking a switch and “causing” a light to go on. J. L. Mackie suggests that what we are often referring to in cases of this type are “INUS” conditions; that is, insufficient but necessary parts of a condition which is unnecessary but sufficient for the given effect. Also, this condition is usually a somewhat unusual situation, as in the case of a circumstance recently introduced into a given situation. Mackie illustrates this analysis with the following example of a shortcircuit causing a fire. Suppose that a fire has broken out in a certain house, but has been extinguished before the house has been completely des­ troyed. Experts investigate the cause of the fire, and they con­ clude that it was caused by an electrical short-circuit at a certain place. What is the exact force of their statement that the shortcircuit caused the fire? Clearly the experts are not saying the short-circuit was a necessary condition for this house's catching fire at this time; they know perfectly well that a short-circuit somewhere else, or the overturning of a lighted oil stove, or any

12 oneofa number of other things might, if it had occurred, have set the house on fire. Equally, they are not saying that the shortcircuit was a sufficient condition for this house's catching fire; for if the short-circuit had occurred, hut there had been no inflammable material near by, the fire would not have broken out... The short-circuit which is said to have caused the fire is thus an indispensable part of a complex sufficient I but not necessary condition) of the fire. (Mackie. 1965)

Of course, it can he pointed out that this INUS condition itself is only part of a causal chain, and thus must also possess a cause. Also, it is often, although not always (an example being lightning “caus­ ing” a forest fire), the case that this INUS condition will be caused by human activity, as in the example of flicking the light switch. Thus, as Collingwood points out, there is often an anthropormorphic element to ordinary discourse about causes. But, as I noted with the lightning example, this human element need not always be present, and even if the sense of causation which I have analyzed in :erms of physical necessity' does not always square with ordinary jsage, it would seem to be usually at least part of what is involved, particularly with the case of causal chains. In any event, this sense of causation in terms of physical necessity would seem to be the sense which is relevant to the causal chains referred to by the causal theory of perception. For example, in visual perception these causal chains at least usually involve the reflection of light from the physical object which is “seen,” the passage of these light rays from that object to the eye, their subsequent refrac­ tion by the cornea and lens of the eye and interaction with the rods and cones of the retina, and the passage of electrical signals along the optic nerve into the neural systems of the brain. Each step in this process is physically determined by an earlier physical state of affairs, and thus my analysis of causation in terms of physical necessity would seem to be the relevant sense of “causation” for what is going on here. I might note that this sense is only applicable to physical causal chains, and thus that the question arises as to how an appropriate brain state resulting from such a chain can in some manner “cause” the nature of our sense experiences, but I shall postpone my discussion of this question until my final chapter. Having thus developed a sense of causation applicable to at least the physical causal chains referred to by the causal theory of percep-

13

tion, I shall now turn to a discussion of some of the major symme­ tries and asymmetries between the physical world, as it is described by the modern atomic theory, and our visual experiences of that world which are causally linked to it. I argued in my last section that there is very little correspondence between the microscopic structure of the physical world and our visual experiences due to the counterintuitive nature of quantum mechanics. In spite of this fact, I wish to show here that with with respect to the macroscopic structure of the physical world there are some important symmetries with our visual experiences, particu­ larly with regard to the spatio-temporal structure of the two. Thus, I will now turn to a discussion of some of the symmetries and asym­ metries between our visual experience and the macroscopic struc­ ture of physical objects being perceived. My discussion here will involve a defense of the classical distinction between primary and secondary qualities.10 The primary secondary quality distinction holds that the only resemblances between our visual experiences and their physical objects involve the primary qualities—i. e., the various spatio­ temporal properties such as size, shape, motion, and position—and that with respect to the secondary qualities—colors, sounds, tastes, smells, hotness and coldness (in their phenomenal senses)—while these possess physical causes, there is no resemblance between the causes and the experiences. I believe that there is much to be said in favor of this distinction. I shall discuss a number of points concern­ ing the primary qualities first, and will then move on to discuss some points concerning the secondary qualities. With respect to the primary qualities, I wish to first argue that both the physical world, as described by modern physics, and at least our visual experiences of that world, share a spatio-temporal format, and I shall then discuss the issue of whether or not there are any important symme­ tries between the two in this regard. Inasmuch as space and time are both mediums which physicists make intrinsic use of in their model of the physical world, I take it that the spatiality of the physical world is sufficiently non-con troversial that it does not need a justifi­ cation here. However, the situation may seem to be a bit different with respect to the claim concerning the spatiality of the perceptual world, since a number of philosophers, including Wilfred Sellars,11 have denied this. The issues concerning alleged problems with the attribution of

14 spatial properties to the mental realm are rather complex, and I will just be concerned here with the issue of whether or not visual expe­ rience itself is spatial, although I might note that in Chapter Five I will also be concerned with the relevancy of this topic to the issue of whether or not the mind is spatially extended. Inasmuch as introspectively visual experience appears as being spread out spatially in front of us, it would seem that some effort would be required to deny this, and thus I think that the denial here is never made just on its own merits, but instead in response to alleged difficulties in ana­ lyses which do attribute spatial properties to the mental realm. Sellars, for example, tries to analyze visual experience propositionally, but this runs into obvious problems in accounting for the visual apprehension of unidentified objects. Of course, it is possible to deny the validity of introspective evidence, and I will discuss the status of this evidence in the last section of this chapter, where I will also discuss the remainder of Sellars’ arguments in some detail. How­ ever, assuming the applicability of introspective evidence, it would seem to follow that visual experience at least is spatial, and I shall ie analyzing both the topologic and metric structure of this space in ny next two chapters. I shall now turn to a discussion of the symme­ tries between the way macroscopic physical objects take up space and their spatial arrangements as they are constituted in our visual spaces. I wish to first point out that in the specific case of visual percepts and a certain class of macroscopic physical objects (which Austinl2 termed “medium-sized dry goods,” such as tables and chairs etc.), there are a large number of geometric correspondences, these being given (with complications due to “size constancy” which I shall analyze in Chapter Three) by projective geometry as the rules of perspective. For example, physical lines which intersect will be projected as also intersecting in visual space (that is, there will be a geometric isomorphism between the two, whereby when physical straight lines share a point in common, so too will the lines in the visual space reconstruction), parallel physical lines will be projected as meeting “at infinity,” and there are even certain metric relation­ ships, related to the “cross ratio,”13 which remain invariant between the two realms. With respect to the secondary qualities, the situation is rather different. While there are some correlations between phenomenal colors and wavelengths of light, and between the pitch of a pheno-

15

menal sound and the wavelength of the sound wave in the air, these correlations are somewhat arbitrary, and there is no direct resemb­ lance involved. In fact, there are even some notable asymmetries here, since, for example, the phenomenal colors merge into each other in a circle—red, orange, yellow, green, blue, violet, and back to red—while the corresponding wavelengths of light are arranged linearly; merging into unperceived infrared radiation at one end of the spectrum, and into unperceived ultraviolet radiation at the other end of the spectrum. Similarly, in the case of audition it can be noted that the phenomenal sounds associated with a piece of music, or the human voice, do not closely resemble the corresponding sound­ waves in the air. There, if anything, is even less resemblance between sensations of heat and cold and their physical causes, the average motion of molecules in the immediate physical surround­ ings. In fact, it is even possible here for the same physical stimulus to produce contrary sensations, such as when after one hand has been placed in cold water and the other in hot water, they are both placed in lukewarm water. It should be emphasized that even though there are resemblances between visual experiences of physical objects and the objects themselves at least with respect to the primary qualities, as I just noted, the two are nevertheless at least numerically distinct. Sine this point concerning the numerical distinctness of percepts ar their physical objects is denied by naive realism, I think that it worth illustrating it with a number of examples. Most of thes examples will involve variations on the argument from illusion. Consider the fact that the speed at which electromagnetic waves, or other physical stimuli (sound waves in the air for audition, chem­ ical stimuli for smell and taste), travel between the physical objects being perceived and the applicable sense organs, is finite, being 300,000 km./sec. in the case of electromagnetic radiation. Thus, it is possible for changes to occur in the physical objects being perceived during the time elapsing between when these waves or other stimuli are emitted from the objects being perceived, and when they reach the applicable sense organs. In the case of quite distant objects, such as stars, these objects may have ceased to exist during this time, or at least moved a sizable distance away, or changed drastically in quality—becoming a supernova for instance in the stellar example. Thus, the question arises as to how a percept which is “sensed” (those who are concerned with the danger of a regress occurring

16

with talk of “sensing percepts” are referred ahead to my discussion of a phenomenal sense of “seeing” at the end of Section 1.3, and of the phenomenal regress argument in Section 4.3) immediately in the present, can be numerically identical with a distant, drastically changed, or even non-existent object. Examples also can be given where an object is perceived in two or more sensory mediums, notably by both audition and vision, where due to the different times for applicable stimuli to reach the relevant sense organs of the different mediums, a single physical event can be sensed as occurring at two different times. The question then can be asked of a naive realist as to which sensory event is to be numeri­ cally identified with the real physical event. One example of this sort is the case of lightning, where the lightning is seen before the thunder is heard; the time difference between the two being depend­ ent upon the distance of the perceiver from the electrical discharge causing both. Other examples along the same line include the cases of viewing a rower in a river some distance away, where the sight of the oars hitting the water is out of synchronization with the sound of the splash caused by the same event, and the perception of an airplane, where the plane is seen in front of the sound emitted from it. It is easy to explain how these inter-sensorially perceived events can be out of synchronization under the causal theory of perception, inasmuch as the degree of this “out of phaseness” can be explained in terms of the different respective velocities of light waves and sound waves. However, these examples would seem to pose great difficulties to a naive realist if he wishes to maintain both the numerical identity of the physical object with the visual and audi­ tory percepts, and the unity of the physical events just alluded to. While his position can be made consistent by either disclaiming this physical unity, or by claiming that only one sensory realm (such as vision) possesses this numerical identity, there is also a pride to be paid here, to the extent that the position then becomes less aligned with that of common sense. A number of similar examples can be cited where an object is not sensed in the same direction as its physical stimulus, including the cases of stereo sound, where the phenomenal sound is sensed as coming from a position in between the two speakers, due to the manner in which the sound waves from the respective speakers are integrated in our auditory sensorial system, and watching a movie, where the words seem to be coming from the actors’ mouths, while

17

Figure I-I

Muller-Lyer Illusion

Hering Illusion

their real source is with the speakers, which may be a considerable distance from the screen. In the case of optical illusions, such as the Muller-Lyer illusion, our sensory system may present perceptual figures whose relative lengths do not correspond to those of the physical stimuli, or in the Hering Illusion, or related illusions, straight physical lines are not presented as being straight phenome­ nally. In the “phi phenomenon,” which occurs in movies, a succession of still pictures is seen as moving. This phenomenon obviously cannot be reduced to the visual apprehension of a series of slightly different images, where each image corresponds to its physical stimulus, since in cases where the stimuli change quite slowly, such as in advertising signs where slowly blinking lights are seen as a movin[ arrow, the motion is still seen as being continuous. Thus, the ph phenomenon would seem to be paradoxical for a naive realist, as then are the subject matters constituted here really moving or not? In double vision—i. e., when the eyes are focused on objects at a given depth, objects at significantly different depths appear doubleare the physical objects also double? Are the objects seen in mirror images where they appear to be? If one gently pushes against the side of one’s eye in monocular vision, the whole visual field will be experienced as tilting, but presumably the physical world does not then also undergo such a tilt, as when an earthquake occurs. If it is conceded that perception is indirect in these cases, it could be argued that it must always be so, since there is no big qualitative difference between cases of veridical perception and cases of illusory percep­ tion. In fairness to naive realists, it should be noted that moves can be made for at least verbally accounting for the preceding purported

18 counterexamples to their position by claiming that we directly per­ ceive only certain aspects (the non-illusory aspects) of the physical objects involved, or that we only perceive them in certain manners. For example, it may be held that in double vision we directly see an object “doubly,” or in response to the time lag argument, it could be maintained that we directly see objects in the past. While I think that verbal moves of this type can probably be made in response to any purported counterexamples to naive realism, I also find them to be extremely unsatisfactory. This is because there always remains the “how question” of how do we directly perceive these distant, past events, no matter how many adverbial qualifications are given. The only answer which I can think of here is to cite the various causal chains, such as the passage of light rays, linking our sensory sys­ tems with these events. However, once this is done, and if these causal chains are going to play any efficacy at all in the explana­ tion, so far as I can see the position becomes identical with that of indirect realism, (the position holding that we are never imme­ diately aware of the physical objects of perception) no matter what it is called. Thus, I conclude that there is a great deal of evidence that physical objects and our phenomenal perceptions of them are never numerically identical with each other, and hence that naive realism is false, and should be replaced by the causal theory of perception. I shall now turn to a section analyzing the language of perception, where I will argue that ordinary perceptual language “hides” the indirectness of perception by failing to make a crucial distinction between our percepts themselves and their physical causes.

19

1.3 Language and Perception

In this section I shall discuss a linguistic point which I think has helped to conceal the distinction made in the last section between our phenomenal experiences of physical objects and the objects themselves; namely that ordinary language does not distinguish between them, and thus tacitly assumes the truth of naive realism. For the purposes of ordinary life we live well enough without distin­ guishing between percepts and their physical objects due to the remarkable, but as I have shown still imperfect, correspondences between the two. Inasmuch as words only enter language when they are needed for some pragmatic purpose, it is not too surprising that ordinary language does not make the distinction. However, in order to properly analyze the nature of the visual perception process, it is absolutely crucial to make the distinction. If one just analyzes ordi­ nary language in order to arrive at one’s theory of perception (as I believe that such ordinary language philosophers as John Austinl4 have done) then one will be covertly led into one of ordinary lan­ guage’s presuppositions, naive realism, without even considering the arguments for or against that position on their own merits. In view of the importance of this distinction between the physical objects of perception and the percepts themselves, I shall now offer a large number of examples illustrating my claim that ordinary lan­ guage fails to distinguish between the two, and showing how certain paradoxes arise from this failure. Consider the riddle of whether there can be sounds in the forest when there is nobody present. Clearly there can be sounds in the sense that there can be sound waves in the air, and equally clearly there would be no reason to believe that sounds in the phenomenal sense of “hearing a sound” would be present, inasmuch as there would be nobody present to have his auditory nervous system stimulated by these sound waves, and subsequently produce phenomenal sounds. Thus, the solution to the riddle is to note the ambiguity of “sound” between a physical sound wave and a phenomenal percept. This solution is “hidden” by ordinary language because it fails to make the necessary distinction between a percept and its physical stimulus. To give another example, consider the various possible rational reconstructions of the meanings of “color.” Is “red” a phenomenal percept, or can there be red objects when nobody is looking at them? What if no light is shining on them? Is an object red when illumi-

20 nated with red light, but where it appears white under normal illum­ ination? What is the definition of “normal illumination”? Is it sun­ light, and if so, what is so special about the mixture of wavelengths of light found in sunlight? Is “red light" red? If so, does it possess the ability to reflect red light, as do other red objects? I do not wish to be dogmatic in answering any of these questions, since it is a matter of convention as to how the word “red” is to be used in ordinary language. The point being made here though is that not only is it possible to distinguish between a phenomenal and a physical sense of colors, as it is with sounds, but that it is also the case that there are a variety of different physical senses; e. g., the ability to reflect light of a certain wavelength, the actual reflecting of that light, the pos­ session of that wavelength (red light), the refracting of that part of the wavelength (rainbows) etc. It is not so much the case that the ordinary usage of color words equivocates among the preceding various uses of color words, as that it is theory laden, covertly assuming a naive realist ontology, and thus assuming that the foregoing distinctions need not be made. Only with a more sophisticated viewpoint, such as that of the ahysical scientist or the perceptual psychologist, can these distinc­ tions be made, and only once the various rational reconstructions of the words have been accomplished under this viewpoint, does the danger of equivocating among the various possible rational recon­ structions arise. The fact that perceptual language has to be rationally reconstructed here should not pose too large of a problem though, since, for example, similar reconstructions have occurred in other fields, notably physics. For instance, how much do the special­ ized meanings of “force,” “power,” “work,” or “energy,” as made use of by modern physics, have in common with the ordinary language usage? The answer might surprise some physicists, although of course something is carried over between the ordinary usage and the rational reconstructions made use of by physics. I shall argue shortly that something very similar will be required in the causal theory of perception for words such as “see” and “perceive,” only unlike the case of physics, where there is only one rational recon­ struction for each of the words taken over from ordinary language, here two quite different types of reconstruction will be required; one phenomenal and one physical. As an example of the danger of equivocation in the rational recon­ structions of perceptual language, consider a type of reductio ad

21

absurdum argument which has been made against the causal the­ ory of perception by Gilbert Ryle15 among others. Ryle argues that inasmuch as when I have a tune “in my head” nobody else can hear it, as by for instance putting a stethoscope against my head, the tune cannot literally be in my head. Similarly, in the case of vision, it can be pointed out that there is no reason for thinking that any region of the brain where phenomenal perception is supposed to take place will possess the same physical color as that being “seen” there, and this fact might then be used in order to argue that such a pheno­ menal experience cannot be located in this region inasmuch as it is of a different color. The weakness in both of these arguments is that they depend upon an equivocation in perceptual language between the phenomenal and physical senses; that is, in “sounds” and “colors” respectively. Once this ambiguity in the rational recon­ structions of these concepts has been noted, any appearance of paradox in the foregoing examples disappears. For instance, it is at least logically possible that a phenomenal color experience could take place in a region of the brain of a different physical color, and an analogous remark holds for sounds. Historically, a number of philosophers, perceptual psychologists, and physical scientists have pointed out at least some of the just noted ambiguities in the rational reconstructions of perceptual lan­ guage, particularly in the case of color. Newton, for example, distin­ guished between phenomenal colors and wavelengths of light in the following passage from his Opticks.

The homogeneal light and rays which appear red, or rather make objects appear so, I call rubrifick or red-making; those which make objects appear yellow, green, blue, and violet, I call yellow-making, green-making, blue-making, violet-making, and so of the rest. And if at any time I speak of light and rays as coloured or endured with colours, I would be understood to speak not philosophically and properly, but grossly, and accordingly to such conceptions as vulgar people in seeing all these experi­ ments would be apt to frame. For the rays to speak properly are not coloured. In them there is nothing else than a certain power and disposition to stir up a sensation of this or that colour, (pp. 124, 125) This passage may also contain the key to resolving Goethe’s dispute with Newton as to whether white is a compound color or not.

22

If white is taken to refer to light waves, then Newton would be correct in his claim that it is compounded of light waves of various wavelengths, and is thus complex. On the other hand, if white is taken to refer to a color percept, then it would seem at least prima facie to be a simple percept, quite unlike the various primary phen­ omenal colors, and Goethe’s claim would be correct. While it may be controversial as to whether Goethe was just referring to pheno­ menal colors in his claim,16 it would seem that to the extent that he was, there need be no disagreement between him and Newton over this issue, due to the ambiguity in “white” between the phenomenal and physical senses. Perhaps the classical philosopher who was the most perspicuous in pointing out the systematic ambiguity in perceptual language between its phenomenal and physical meanings was Thomas Reid, who, in his works An Inquiry into the Human Mind, and Essays on the Intellectual Powers of Man, repeatedly points out how the failure to take note of these ambiguities has led philosophers into error. The following two passages are perhaps representative of these argu•nents.

We have all the reason therefore, that the nature of the thing admits, to think that the vulgar apply the name of colour to that quality of bodies which excites in us what the philosophers call the idea of colour. And that there is such a quality in bodies, all philosophers allow, who allow that there is any such thing as body. Philosophers have thought fit to leave that quality of bodies, which the vulgar call colour, without a name, and to give the name colour to the idea or appearance, to which, as we have shown, the vulgar give no name, because they never make it an object of thought or reflection. Hence, it appears, that when philosophers affirm that colour is not in bodies, but in the mind; and the vulgar affirm, that colour is not in the mind, but is a quality of bodies; there is no difference between them about things, but only about the meaning of a word. (Inquiry, p. 103) The vulgar confound sensations with other powers of the mind, and with their objects, because the purposes of life do not make a distinction necessary. The confounding of these in com­ mon language has led philosophers, in one period, to make those things external which really are sensations in our own minds; and in another period, running, as is usual, into the contrary extreme, to make almost everything to be a sensation or feeling in our minds. (Essay, p. 130)

23

Reid makes some very insightful remarks in both these passages as to how the failure of ordinary language to make a distinction between percepts and their physical objects, has led philosophers into unwarranted assimilations of one into the other, in either direc­ tion. It should be emphasized that I am not endorsing Reid’s theory of perception here (for example I disagree with his critique of representationalism), but merely showing that he makes the same distinc­ tions which are necessary for a coherent causal theory of perception. Also, a number of recent philosophers have argued that there are systematic ambiguities in perceptual language, and thus, like Reid, trace paradoxes in theories of perception to linguistic problems. Perhaps the following selections respectively from Nicholas Pastore and C. D. Broad are representative of this literature. Pastore writes: Other basic recurring terms in the literature of perception which also have dual meanings include “sensation,” “distance,” “visible object,” “visual field,” “field of vision” and “light.” Thus “visible object” may be descriptive of the external object or of the original perception, and “sensation” may refer to nervous excitations or to the psychic concomitant of excitations. Since the meanings of a particular term are often freely interchanged by a theorist without an explicit reference to this shift, ignorance of this fact may account for the apparent self-inconsistency in his theory and the failure to understand the explanation that he might give for the acquisition of some perception. (Selective History of Theories of Visual Perception 1650-1950, p. 261) Thus, Pastore claims that there is an ambiguity in such phrases as the “object of perception” between the physical objects causing the occurrence of these perceptions, and the objects constituted in our phenomenal fields which both common sense and idealist philo­ sophers mistakenly take to be numerically identical with them. Pastore’s point here is valid if he is just referring to the rational reconstructions of these phrases, and not to their ordinary usage, which I have argued is theory laden (implicitly assuming the truth of naive realism) rather than itself being ambiguous. Broad in the following passage claims that there is a similar ambiguity in the perceptual verbs “perceive,” “see,” “hear,” etc. A result of this is that all words like “seeing,” “hearing,” etc., are ambiguous. They stand sometimes for acts of sensing, whose objects are of course sensa, and sometimes for acts of perceiving,

I

24 whose objects are supposed to be bits of matter and their sensible qualities. This is especially clear about hearing. We talk of “hearing a noise” and “hearing a bell.” In the first case we mean that we are sensing an auditory sensum, with certain attributes of pitch, loudness, quality, etc. In the second case we mean that, in consequence of sensing such a sensum, we judge that a certain physical object exists and is present to our senses. Here the word “hearing” stands for an act of perceiving. Exactly the same remarks apply to sight. In one sense we see a penny; in another sense we see only a brown sensum. (Scientific Thought, p. 248)

This issue of whether or not the ordinary usage of the word “see” is ambiguous or not turns out to be rather controversial, and has for example been the subject of a debate between A. J. Ayer and John Austin. I think that it is worthwhile to examine this debate in some detail. Ayer,17 for example, cites the case of seeing a star in this regard, noting that one may either describe the experience as that of seeing a body much larger than the earth or in terms of seeing a tiny silvery speck. He goes on to note the inconsistency in claiming to see, in the same sense, entities of such disparate sizes, concluding that the; e must be two different senses of “see” involved here. Aus­ tin however argues, citing ordinary usage, that “see” is not ambigu­ ous, and that it always refers to the perception of material objects, or at least to physical phenomena (rainbows, shadows etc.). He makes this point as follows: Suppose that I look through a telescope and you ask me, ‘what do you see?’ I may answer (1) ‘A bright speck;’ (2) ‘A star;’ (3) ‘Sirius;’ (4) ‘The image in the fourteenth mirror of the telescope.’ All these answers may be correct. Have we then different senses of ‘see’? Four different senses? Of course not. The image in the fourteenth mirror of the telescope is a bright speck, this bright speck is a star, and the star is Sirius; I can say quite correctly and with no ambiguity whatever, that I see any of these. (Sense and Sensibilia, p. 99) I do not wish to be dogmatic in deciding who is correct in this debate as to whether “see,” in its ordinary usage, is ambiguous or not. Austin has a point in that several of what may appear superfi­ cially to be different senses, such as seeing a bright speck as con­ trasted with seeing a star, may just involve varying degrees of assurance as to what is being seen, and thus there may be no

25 contradiction in holding that the bright speck is a star. But if “bright speck” is being used in a phenomenal sense, or even in Austin’s sense of being an image in a mirror of a telescope, it would seem to be contradictory to hold that it is also a star, since stars are neither phenomenal objects nor images in telescopes. Ayer, also in this regard, cites the claim of a drunkard to “see pink rats,” and if this example is allowed to stand it would seem that the word “see,” in at least one of its senses, can be used to refer to phenomenal objects, as in this case there are no physical rats to be seen. In any event, it does seem to be the case that at least the dominant meaning of “see,” as made use of by ordinary language, entails both that when we see an object we are immediately aware of what we are seeing, and also that this object persists in the same format when nobody is perceiving it. Thus, the dominant ordinary use of “see” implicitly assumes a naive realist metaphysics, since only under that metaphysics do both of the foregoing principles hold. Before going on to examine possible rational reconstructions of “see” which do not assume the truth of naive realism, I wish to make note of two further features of the ordinary usage; that the object “seen” is slippery in the sense that a whole object can be seen “in virtue of’ just seeing a part of it, and that it is what Rylel® calls an “achieve­ ment word” inasmuch as one cannot see something if it does not exist. I shall examine this slipperiness of objects being seen first, and will then move on to examine Ryle’s point. It might be argued that we never see the whole of physical objects since at the most we are just immediately aware of their surfaces and not their backsides or interiors, and I will have more to say concerning this feature of visual perception in my next chapter. However, as a host of linguistic philosophers have pointed out,19 the word “see,” at least as ordinarily used, is like the word “kick” in that we see or kick the whole object and not just part of it. This does not mean that I am aware of every part of an object when I see it any more than that my foot must be in contact with every part of a ball when I kick it, but rather that, as Frank Jackson20 notes, I see an object “in virtue of’ being immediately aware of part of it, just as I kick the ball in virtue of having my foot come in contact with part of it. Jackson points out this feature of the grammar of the ordinary usage of “see” as follows: We commonly see things in virtue of seeing other things: I see the aircraft flying overhead in virtue of seeing its underside (and

26 the aircraft is not identical with its underside); I see the table I am writing on in virtue of seeing its top; I first see England on the cross-channel ferry in virtue of seeing the white cliffs of Dover; and so on and so forth. (Perception a Representative Theory, p. 19) It is a bit vague where this property of the slipperiness of the object seen breaks down—certainly I do not claim to see the universe in virtue of seeing a small part of it—but in any event it is unclear where the exact grammatical boundaries are. The second aspect of the grammar of the ordinary usage of “see” which I would like to discuss now is that it, like “know,” is an “achievement” word, in that it assumes the success of its operation. That is. it is impossible to know what is false or to see what does not exist due to the very meanings of “know” and “see.” Of course, one may mistakenly believe that one knows something which is actu­ ally false, or mistakenly believe that one is seeing something when it actually' does not exist, but one cannot actually know or see them, as Ryle points out as follows:

Just as a person cannot win a race unsuccessfully, or solve an anagram incorrectly, since “win" means “race victoriously" and “solve” means “rearrange correctly,” so a person cannot detect mistakenly, or see incorrectly. To say that he has detected some­ thing means that he is not mistaken, and to say that he sees, in its dominant sense, means that he is not at fault. It is not that the perceiver has used a procedure which prevented him from going wrong or set a faculty to work which is fettered to infallibility, but that the perception verb employed itself connotes that he did not go wrong. (Concept of Mind, p. 238) Thus, it can be objected against the causal theory of perception that according to at least the dominant ordinary use of “see,” we do not “see” percepts, or even “perceive” them, inasmuch as these verbs refer instead to the successful apprehension of physical objects or other physical phenomena, which are not percepts. While Austin and Ryle may be correct here in their analysis of the domi­ nant ordinary use of “see,” I wish to argue that this is only because of the implicit assumption of naive realism by ordinary language which I have already pointed out. Once the relevant senses of “see” and “perceive” have been rationally reconstructed without this assumption though, these words become ambiguous, possessing

27 either a physical sense, in which they refer to the physical “causes” of what is phenomenally present, or a phenomenal sense, in which they refer to the apprehension of what is immediately presented to us by our senses (and where one does not also “see” something else in virtue of “seeing” this). Something should be said about both of these senses, and I will start with the phenomenal sense. The first thing to note about the phenomenal sense of “see” is that it must be a non-relational sense (i. e., it must collapse the distinction between the seer and what is seen), since otherwise a regress will result in that something else will be required to “see” visual per­ cepts, and so on indefinitely. Of course the “object seen” here will not be numerically identical with the whole seer (in the sense of being the conscious mind), but only part; i. e., the region of the seer’s visual space that is numerically identical with the phenomenal “object.” I might also note that I will analyze the nature of the purported phenomenal regress here in detail in Chapter Four. As for the physical sense of “see,” wherein it is claimed that we “indirectly” see physical objects, a major problem lies in identifying where along the causal chains of light rays terminating in our retinal images the “objects” being “seen” are located. It is some­ times contended here that what we really see are just patterns of light or even our retinal images, but such claims are not very practi­ cal and do not correspond with ordinary language claims about what physical phenomena are being seen. One could also define a sense which designates the object of perception here as being the last physical object to reflect the light impinging on the retina for a given angle of view, but this sense would also not seem always to be apropos, both since sometimes, as in viewing the sky, other optical phenomena besides reflection are the relevant ones for picking out the object, and because in cases of seeing something in a mirror, one does not want to pick out the surface of the mirror as being the object seen, but instead the object whose image is reflected in the mirror. Instead, a much more practical sense is one which identifies these objects in terms of information being preserved between the object and our experience of it, and an interesting analysis has been given of this sense by Fred Dretske.21 Dretske identifies the object of perception with the object which is given “primary representation” by the perceiver in the sense that if an object fs properties are learned about by means of the representation of the properties of an intermediary c (such as a mirror image or a retinal image), but where

28

the reverse relationship does not hold, the primary representation is given to fs properties and not to c's. A complication for this approach might seem to occur in cases of seeing things in movies or on television, since there even though information is invariant between our visual experience and what is seen in the movie or on television, in at least ordinary language we would not say in an unqualified sense that we see these things, but rather that we saw something “on television” or “in the movie.” I think that this shows that the ordinary language sense of “see” presumes that vision is an optical phenomenon, whereas some of the causal links in these last cases obviously does not just involve optics. Thus, it might be better for this reconstruction just to deal with information invariants when all of the causal intermediary steps are optical. Thus, using the phenomenal rational reconstructions of “see” and “perceive,” we can refer to our apprehension of what is immediately presented to us in vision without interpreting its status (as naive realism does by holding that it is part of the surface of a physical object), and it will be with this sense that I shall be primarily concerned in this book. Of course, the other rational reconstructions of “see” and “perceive” which refer to the indirect apprehension of physical objects are also worthy of analysis, particularly concern­ ing the question of the ontological status of the physical objects which are indirectly perceived. However, while I find these ques­ tions to be intriguing, I shall not be concerned with them here. I shall now turn instead to a discussion of the change of attitude away from that of common sense and naive realism which is necessary in order to analyze the nature of what is phenomenally immediately present to us in visual perception.

29 I. 4 The Attitudinal Shift to Visual Space

I have shown in the last three sections of this chapter that the naive realist attitude held towards the world by common sense; i. e., that we are immediately aware of at least the frontal surfaces of physical objects being seen, has been shown by the findings of the physical sciences to break down. Thus, what that attitude takes to be physi­ cal objects which are publicly observable by more than one person, are in fact constructs from the individual private phenomenal expe­ riences of particular perceivers. The physical world which is per­ ceived by more than one person is never directly perceived, in the sense that it is never immediately present in any person’s sense experiences, and is instead only learned about by means of the hypothetico-deductive method of the physical sciences. That is, the atoms and their constituent particles, whose existence is postulated by these sciences, are never the immediate objects of perception, although their existence is testable by means of making predictions about their empirical consequences (the phenomenal results of their causal interactions with our perceptual systems). Thus, in order to properly analyze the true nature of what is immediately present to us in vision, one must forgo this naive realist attitude towards one’s visual percepts, and instead regard these percepts from a more neutral standpoint, as being a field of colors (in the phenomenal sense of colors) of various hues, sizes, and shapes, leaving open the question of whether or not physical objects are constituted in it. In other words, one must regard one’s visual per­ cepts from the same standpoint as that of an artist, as a scene in perspective, in which the question of the ontological status of that scene does not arise. Edmund Husserl, in Ideas, analyzed this change in attitude in what he termed the enoxr], or “bracketing,” where questions of whether or not we are immediately aware of physical objects are “bracketed,” and instead a pure phenomenology is performed; i.e., phenomenal experience is described in and of itself. J. J. Gibson, in The Perception of the Visual World, also discussed this subject, contrasting the respective perceptual experiences re­ sulting from these two attitudes, which he termed those of the “visu­ al world” and of the “visual field,” as follows:

The field is bounded whereas the world is not. The field can change in its direction-from-here but the world does not. The field is oriented with reference to its margins, the world with

30

reference to gravity. The field is a scene in perspective while the world is Euclidean. Objects in the world have depth-shape and are seen behind one another while the forms in the field approx­ imate being depthless. In the field, these shapes are deformed during locomotion, as in the whole field itself, whereas in the world everything remains constant and it is the observer who moves, (p. 12) I do not find the perceptual differences between the visual field (what I call “visual space”) and the visual world which Gibson alludes to in the preceding passage, to be as great as he makes out. For instance, I do not see why depth perception cannot be present under the attitude of the visual field, since certain colors in the field may be experienced as being more distant than others, and there also seems to be a primitive sense of up and down under both attitudes. Admittedly, a number of differences between the two atti­ tudes still remain, as, for instance, under the attitude of the visual world, one would claim to see one object blocking the view of another, while under the attitude of the visual field, this second object would simply be considered to no longer be constituted in the field. These differences would seem to be due to either inferences from or interpretations of what is visually immediately present, however—e. g., in this case being due to an assumption that objects continue to exist in the same format when they are no longer being observed—while what is immediately given to visual experience would seem to remain the same under both attitudes. This last point even applies to Gibson’s remarks concerning changes in geometric structure between the two attitudes. Lines and angles, as constituted visually, do not “jump” when a switch in attitudes takes place. Thus, any change in the way in which these lines and angles are characterized must instead be due to a change in what they are held to represent; i. e., either the geometry of what is immediately given visually, which I shall argue results in a twodimensional projective geometry, or the geometry of the surfaces of the physical objects which it is held that we are immediately aware of, which would be Euclidean, inasmuch as these objects can be shown by means of physical measurements to possess a Euclidean geometry. Another way to analyze the attitude of the visual world here, and a way which is developed in some detail by Patrick Heelan in Space Perception and the Philosophy of Science with regard to the Lune-

31 burg theory of visual space, is to emphasize the interpretive aspect, which goes along with the naive realism, of that attitude towards events occurring in visual space. The detailed study of these inter­ pretations is known as “hermeneutics,” and this discipline is even developed into giving an account of the theoretical entities postu­ lated by physics by Heelan; where, forexample, he even claims that electrons are directly seen by scientists. Of course, I am defending the causal theory of perception and a realist ontology for physics in this book, but even while this approach is in direct opposition to Heelan’s approach to the philosophy of science, there nevertheless may be considerable merit in his analysis of the results of a naive realist attitude towards our immediate visual experiences. In any event, in order to undergo a detailed geometric analysis of our visual experience per se—i. e., under the attitude of what Gibson calls the “visual field”—an attitudinal shift will have to be made away from naive realism to a more neutral standpoint under which the experience can be analyzed in and of itself, without at least any substantial changes occurring in the nature of the visual given due to this change in attitudes. Obviously, this phenomenological anal­ ysis cannot be performed at least directly by means of making physical measurements, such as by using a ruler, since there is n reason to assume that the geometric structure of the visual field wi. be the same as that of the physical objects being indirectly per ceived, and thus instead it will have to be based on introspection. In view of the controversy which has occurred during this century regarding the efficacy of introspection as a methodology, I shall now, in my final section of the chapter, offer a justification of the use of it.

I 32

1.5 The Legitimacy of Introspective Evidence To begin my discussion of the legitimacy of using introspective evidence in discovering the geometric structures of our phenomenal experiences, I first wish to take note of a gap between our immediate visual experiences and judgments about them. This gap occurs because judgments are propositional, and hence verbal, in charac­ ter, whereas I am arguing that visual experience, per se, is spatial in character, and hence non-verbal. It is still clear though that we are capable of making introspective judgments concerning various geometric, including metric, properties of our visual experience, such as by judging what proportion of the total visual space is taken up by an object as it is constituted in it, or by comparing the relative sizes of the constituted objects. However, the question does arise here as to whether these introspective judgments are veridical or not, and it is this epistemic gap which Wilfred Sellars exploits in his discussion of the “myth of the given.”22 I shall deal with Sellars’ arguments in some detail in this section. Sellars’ argument is quite complex, and I shall mainly just deal with two aspects of it here; the discussion of the existence of the epistemic gap just pointed out between our visual experiences and our judgments about them, and the claim that since the language of perception has been publicly defined, there is no guarantee that our descriptions of our private sense experiences (assuming that they possess the characters of particulars, whereas Sellars claims that they in fact are linguistic in character and hence, he argues, really universals) will conform to the public notions. This second point is related to Wittgenstein’s23 private language argument, in which he argued that since the meanings of words are their uses in public language games, it is impossible to develop a purely private lan­ guage (Wittgenstein asks, for example, how in a purely private language it would be possible to verify that we are using the words in the language correctly). Regardless of the merits of Wittgenstein’s argument here as an argument against the possibility of a purely private language, I think that it at least shows that if words are to be publicly understood then their meanings must be publicly accessi­ ble, and I do wish to argue that our introspective reports of our private sense experiences can be publicly understood. I shall now turn to the details of that argument, and will then return to a discussion of Sellars’ first point concerning why we should think

33 that introspective reports concerning our sense experiences are veridical. I will start this discussion of why I think that it is possible to refer to private sense experiences by means of words in a public language by making some points concerning the distinction between “public” and “private.” I will then link these remarks with some analogous points concerning the distinction between “objective” and “subjec­ tive.” The analysis of “private” is quite straight-forward as that which is not accessible to more than one person, and obviously sense experiences are private in this sense. The analysis of “public” is more complex though, and in fact I wish to argue that the use of “public” in ordinary language is theory laden, since it assumes the truth of naive realism when it makes such claims as that we are all publicly immediately aware of the same physical objects. Since I have argued that naive realism is false, it is necesssary to rationally reconstruct this sense of “public.” This can be done in two possible ways; either by referring to the physical objects which I have argued are only indirectly perceived by being linked by causal chains with our experiences of them, or by referring to “intersubjective” expe­ riences.24 It is difficult to give an adequate analysis of the “intersub­ jective” in a short space here since different people’s experiences of objects are qualitatively different (for instance, they see them in perspective from different angles of view), but at least perceptual invariants, such as the cross ratio previously mentioned, could be pointed to for connecting experiences of the same objects among different people. In this last sense of “public,” as the intersubjective, the public color of an object, for instance, would be defined as being the phenomenal color sensation which is sensed by normal observ­ ers under normal circumstances. I now wish to point out that there is an analogous ambiguity in “objective” to the one just pointed out in my rationally reconstructed senses of “public” between that which is of the objects being observed, as opposed to being of the subject (the observer) and that which is objectively true in the sense of being intersubjective. Hegel pointed out this ambiguity as follows:

First, it (objectivity) means what has external existence, in distinction from which the subjective is what is only supposed, dreamed, etc. Secondly, it has the meaning, attached to it by Kant, of the universal and necessary, as distinguished from the

34 particular, subjective, and occasional element which belongs to our sensations. (Hegel’s Logic, p. 68)

Similarly, “subjective” is ambiguous between that which is imme­ diately present to consciousness, and thus private, and that which is non-objective, in the sense of varying among different individuals. With the preceding distinctions between “private” and “public,” and “subjective” and “objective,” in mind, Wittgenstein’s private language argument can be replied to as follows. I am willing to concede what I take to be Wittgenstein’s basic insight, that the meanings of words must be public, but the question arises as to which sense of “public” is relevant here. I have already argued that the sense of “public” which assumes the truth of naive realism is non-referential, and I will now argue that the relevant sense of “public” which should be substituted for it is that of the intersubjective. Obviously, the sense of “public” which refers to objects which are only indirectly perceived is not relevant here, since the mean­ ings of words in a language are apprehended immediately in con­ sciousness and not indirectly as this sense would require. This leaves the sense of “public” which refers to the intersubjective, and it can be seen that this sense is apropos by noting that even though what is “public” in the sense of being intersubjective is also “pri­ vate” in the sense of pertaining to individuals’ phenomenal sense experiences. So long as other people have similar experiences, the same words can be used intersubjectively to talk about them. There is still the problem of showing that the private experiences just referred to are in fact the same (or involve the perceptual invar­ iants mentioned in my analysis) for different people, which is a problem often illustrated by the inverted color spectrum problem of how do I know that your color percepts are not the reverse of mine for identical physical stimuli. I have two distinct points to make here. My first point is that this problem is analogous in structure to the other minds problem of how do I know that other people possess minds, in the conscious sense, and are not merely automata. I would argue that even though our knowledge is not indubitable in either case, we still have reasonably strong inductive arguments for hold­ ing these beliefs. In particular, I would cite the inductive argument from analogy that since other people are biologically similar to myself and possess similar origins, since I possess a consciousness where certain color percepts are associated with particular physical

35

stimuli, by analogy they will also. Of course, there is not any way to conclusively verify that this is the case, and it must also be admitted that the strength of this type of inductive argument by analogy is controversial,25 but nevertheless, I believe that it lends at least some credence to the conclusion. My second point is that regardless of the merits of the foregoing argument, in the case of the geometric properties of visual space with which this book is concerned, it is possible to use statistical methods to see if there are significant correlations among various introspective reports from different subjects. However, it must be noted that the results here depend on the nature of the instructions given (this is particularly apparent in the literatures on size and shape constancy),26 but I will still argue that in the case of a certain class of instructions, those where a subject is asked to judge an object’s projective properties, veridical information is available. Since the question of the veridicality of introspective reports con­ cerns essentially the same issue as Sellars’ first argument about the gap between experiential reports and the experiences themselves, I shall now close the chapter by discussing the merits of that argument. Essentially, Sellars’ argument here is that inasmuch as knowl­ edge claims concerning sense experiences are propositional in nature, whereas sense data theories assume that the sense experien­ ces themselves are not propositional (a claim which Sellars goes on to dispute), then there is a gap between the two, and thus the ques­ tion arises as to how the knowledge claims here are to be justified. In reply to Sellars, I would first point out that we are introspectively aware of the whole of our visual spaces and can thus, for example, introspectively compare lengths of objects constituted in those spa­ ces, and then make verbal reports of the magnitudes of these lengths. Similarly, we seem to be able to tell the difference between a straight line in visual space and a curved one, and can report this difference. I do not claim that these verbal reports are infallible, since for example it is always possible to at least misdescribe these experiences, such as when we use a word incorrectly (say a wrong color word) according to its public (in the sense of intersubjective) definition. Also, there may be times, as Ayer24 emphasizes, when we cannot tell whether our sense experience actually possesses a given property or not, such as, for example, when two lines as they are constituted in visual space possess almost exactly the same lengths,

36 we may not be able to tell which is longer. Still, in most cases we are able to make verbally unambiguous judgments concerning clear-cut properties of our sense experiences, and the question arises as to whether or not we are justified in believing that these judgments are correct. The best answer which I can think of to this question is to point out that the evidence upon which these experiential judgments are made is the same evidence upon which judgments concerning the nature of physical objects being perceived are made under the attitude of naive realism. Thus, introspective judgments should be every bit as veridical as judg­ ments about physical objects based upon our perceptions of them. It could be objected here that the brain is capable of bypassing con­ sciousness in making at least some decisions based on sensory stimuli, since, for example, in the phenomenon of “blind sight” people are still able to respond appropriately, to at least a limited extent, to visual stimuli after the loss of the visual cortex and claim­ ing to be unable to see,25 and I will have more to say on this subject n Chapter Five. However, responses to visual stimuli in “blind ight” are extremely limited in nature, and thus it would seem that t least usually responses to sensory stimuli involve transmission .hrough a conscious component. It would seem then that there is no inherent reason either for thinking that we cannot use a public (in the sense of intersubjective) language for communicating about our private (in the sense of phenomenal) sense experiences, or for thinking that introspection must be unscientific, since intersubjective reports of private sense experiences can be checked for consistency and by other statistical tests. This concludes my study on the legitimacy of introspection as a methodologyy, and in my subsequent two chapters I shall use introspective evidence in giving an analysis of the geometric struc­ ture of visual space; first with its topology, and then with its metric structure. In my final chapter, I shall return to some of the mind body questions raised in this chapter regarding how a causal con­ nection may be possible between physical events in the brain and phenomenal ones in visual space.

CHAPTER TWO THE TOPOLOGY OF VISUAL SPACE With a little good will we can give it (visual space) three dimensions. Henri Poincare, Demieres Pensees

Topology, sometimes referred to as "analysis situs,” is the study of those properties of a space which remain invariant under continuous transformations; that is, under such transformations as bending, stretching, or squeezing, but not under breaking or tearing. Two points which are near each other in a given space will remain near each other in a topological transformation of that space, and thus a triangle is topologically equivalent to a circle but not to a straight line, and a cube is topologically equivalent to a sphere but not to a torus. In this chapter I shall investigate the topology of visual space, paying particular attention to questions of continuity, dimen­ sionality, and boundedness. It will turn out not to be possible to rigorously deduce the topology of visual space, since, as A. A. Blank,1 a major commentator on the Luneburg theory that visual space possesses a hyperbolic metric structure, notes, "the concept of open set is not readily applicable to visual experience.” Still, I think that it is possible to strongly motivate a particular topologic struc­ ture, and I will be doing this throughout the chapter. A central issue in my discussion of the continuity of visual space will concern the distinction between the continuity of the space and the question of whether or not it is homogeneous, and an important distinction in my analysis of the dimensionality of the space will be that between the actual dimensionality of the space and the question of whether or not we possess immediate (non-inferential) pheno­ menal depth perception. I shall begin my discussion of the dimen­ sionality of visual space with a digression into the various defini­ tions which have historically been proposed for "dimension” in order to find one which may serve as a criterion by which the dimensional­ ity of visual space may be tested.

38 The dimensionality of visual space has been the subject of a long controversy among philosophers and psychologists of perception, with one group, including Berkeley,2 Thomas Reid,3 Helmholtz,4 Carnap,5 and R. B. Angell,6 having held that it is two-dimensional, while another group, including Poincare,7 C. D. Broad,6 William James,9 J. J. Gibson,10 and Rudolf Luneburg,! 1 having held that it is three-dimensional. There has also been a controversy as to whether the metric structure of visual space is Euclidean, hyper­ bolic, or spherical, and it is noteworthy that those holding that it is spherical, such as Reid, Helmholtz, and Angell, have also held that it is two-dimensional, while those holding that it is hyperbolic, the members of the Luneburg school, have held that it is threedimensional. I shall examine these metric questions in detail in my next chapter. Inasmuch as much of my analysis of the dimensional­ ity of visual space will presume that it is a continuum, I shall deal with the question of the continuity of visual space first, to be fol­ lowed by my analyses of its boundedness, and finally, its dimen­ sionality.

39

2.1 The Continuity of Visual Space In this section I shall investigate the question of whether or not visual space is either continuous or at least piecewise continuous (i. e., only possesses a finite number of discontinuities). Inasmuch as both my analysis of the dimensionality of visual space, and my chapter on its metric structure (which will make intrinsic use of differential geometry and will thus postulate the existence of differ­ entials in visual space) will presuppose at least the piecewise conti­ nuity of visual space, an affirmative answer here will be crucial to my later analysis. I shall first give a brief analysis of what it means fora space to be continuous, and will then investigate whether or not visual space meets the criteria given. It should be emphasized at the beginning that much of this analysis is derived from issues in number theory—e. g., the issue of whether the set of real numbers is continuous or not—and thus, many of the criteria being discussed will not be at least directly testable for in the case of visual space. The property of being continuous must be distinguished from the property of being dense—that is, for a space to contain a point in between any two of its points—inasmuch as a model can be given, such as bj' the rational numbers, of a set which is dense yet not continuous (the set of rational numbers excludes the irrational numbers which are nevertheless part of the continuum of the real numbers). A criterion for being continuous is suggested here though, that being that if it is possible to map a section of the real number continuum onto a segment of a space, then that space must be continuous. This criterion presupposes an analysis of the real number continuum however, and thus I shall now turn to such an analysis. Cantor1- defined a continuum as being a compact connected set. A set is compact if each infinite subset of it contains at least one limit point in the set, while a set is connected if it cannot be separ­ ated into two non-vacuous, disjoint, open sets. Open sets arc sets which extend indefinitely in the sense of not containing their boun­ daries; that is, for every point in such a set, there is a sphere of radius greater than 0, all of whose points are also contained within the set. A limit point can in turn be defined as being a point X such that for any e, there is a point such that:

0 < | x-y |


(3.13)

e' = C - 1/ag

(3.14)

C is the radius of a visual space in which all of the objects consti­ tuted in the space are infinitely distant, and a is a proportionality constant. My hypothesis now is that these transformations consti­ tute an external description of the geometry of visual space, whereg' gives the distance to a point in visual space in the direction 0', ', from a point in the three-dimensional overall space which is not also in visual space (the center of the sphere in the special case where q is the same in all directions). It can be noted that q' approaches© when op approaches 1/C, but inasmuch as there exists a minimum thre­ shold on the depth at which physical objects can be brought into sharp focus, about six inches from the eye, this result is consistent with the facts about visual perception; i. e., due to the presence of a “cutoff’ point. Also, it is possible that the transformation repres­ ented by Equation 3.14 would need to be more complex than it is given here, possibly even varying among different individuals, in order to fully account for the size constancy tendency. However, due to the controversy as to what the precise quantitative nature of that tendency is, it would seem to be judicious to keep the transformation as simple as possible for the present. Its general format in any event seems to be correct, inasmuch as the tendency towards size con­ stancy is greatest when the objects being constituted in visual space are relatively close, and since size constancy experiments yield results approaching a null match as these objects become more distant. A few remarks should also be made here with regard to the onto­ logical status of the three-dimensional overall space in which visual space has been characterized as being embedded. In one of the

109

theories which I shall investigate in my last chapter it will be suggested that this space is physical, with visual space being curved with respect to a structure of the brain. For present purposes though it can be thought of as being just a heuristic device (which possibly also possesses a physical interpretation) for discovering the inter­ nal geometry of visual space. While this internal geometry, of course, does have immediate phenomenal significance, being the metric structure of a coordinate system embedded in phenomenal visual space itself, it needs to be emphasized that such variables in the external geometry as g' which connect points in visual space with non-phenomenal points in the overall space (for q this thirddimensional point is the center of the sphere in the special case where visual space is spherical) possess no immediate phenomenal significance. Thus, there is no reason, for example, to believe that they correspond to perceived depth. I shall now turn to my discus­ sion of the internal geometry of visual space. Inasmuch as my treatment of the internal geometry of visual space will assume that the space is not only differentiable, but also locally Euclidean in the metric sense defined in Section 3.1, with the exception of a finite number of discontinuities, it should first be examined whether or not such assumptions are reasonable. It will turn out that there is no way to rigorously prove that visual space possesses ei th er of these properties, and thus at various stages in the following arguments I shall just assume that it is at least piecewise smooth, and hence differentiable, and also that it is locally Eucli­ dean in the metric sense. The following considerations should help to motivate the claim that these assumptions are not unreasonable though. Inasmuch as 1 have placed a boundary condition on the values allowed for g, OQ > 1/C

(3.15)

it follows that a visual space will be differentiable if the twodimensional physical manifold represented by f(9, t), that is the manifold of physical surfaces being seen, is differentiable. It should also be recognized that the transformations from physical space to visual space, given by Equations 3.12 - 3.14, are somewhat of an idealization due to the finite resolving power of the eye and thre­ sholds in its ability to distinguish between different physical depths. 'Phus, the fact that from a microscopic perspective physical

110

surfaces are not even piecewise smooth, and the fact that a very distant physical manifold, such as the night sky, may possess a large number of large physical discontinuities, do not mitigate the claim that the corresponding sections of visual space are differenti­ able, due to these visual thresholds. It is only in cases where there are significantly large discontinuities or sharp corners in the spatial arrangements of relatively close physical objects, such as in cases where one object partially occludes the view of another, that visual space itself will not be differentiable, or will possess discontinuities. It should also be pointed out that a visual space, thus defined, seems to be locally Euclidean in the metric sense, since as I pointed out when I argued that the global metric structure of visual space is spherical, figures in the small in the space seem introspectively to possess a Euclidean metric. I shall now turn to the actual derivation of the internal geometry of visual space. Consider the surface of a sphere of radius r centered at the same third-dimensional point as a given visual space (i. e., whereg' = 0), intersecting a given point of the visual space (thus at this point r = g'), as in Figure 3-8. Working with differentials, the question can be raised as to how a deviation away from the surface of the sphere by the visual space, dg ( dg of course is determined by means of the depth function/?#, t), causes a deviation in the metric structure of the visual space away from that of the sphere. If dl is a differential on the surface of the sphere, and assuming that visual space is differentiable here and also locally Euclidean in the metric sense, the differential in visual space ds (which is the only differen­ tial being used here which actually possesses phenomenal signifi­ cance) will be determined by the Pythagorean theorem as follows:

ds2 = rg2 + dl2

(3.16)

dg' is given by dQ

= ^90' + &dff. 90 de

(3.17)

and dl2 corresponds to the metric of a sphere; i. e.,

dl2 = [d02 + sin26 dd2] r2 (3.18) wheie 9 and 'j are spherical coordinates whose values are coordi­ nated with 6 and In view of this coordination, I shall substituted

Ill

de'

Surface of sphere of radius r

dl

Il

Figure 3-8

and < for 0' and ds2

ae

from here on. It follows that:

de2 + 2

30 a

d0 d$ + 1®. dp + [d02 + sin28 de2] r2

a4>

(3.19) Since we have been working with differentials here, g' can be substi­ tuted for r, and thus the internal geometry of visual space in terms of the line element is given by:

ds2 = { Q2 +

) de2 + 2 ££ded^ + /££ + Q2sin2e) dp de ' ao a ’ a$ ' • (3.20)

which corresponds to a deviation on the metric structure of a sphere determined by the depth function f(B, t).

112 In order to determine actual distances in visual space, ds must be integrated; i. e.,

e'2 +

) de2 + 2^_ 99 /

99 a$

d9 dtf + / ! a$

+ e'2sin29 j d92 /

(3.21) The degree of difficulty in evaluating this integral depends upon the nature of the depth function f(9, j>, t), which of course can possess very odd properties. Nevertheless, in areas where visual space is differentiable, it will generally be possible to evaluate this integral using a computer program, but I will not attempt any such integra­ tions in this chapter. Having thus shown how the internal metric structure of visual space can be derived from the assumptions that it is a twodimensional space whose global metric structure is spherical, and whose local metric structure is determined by a depth function so as to accommodate the size constancy tendency (although of course this global structure is fully determined by integrating the local structure), the question arises as to whether or not such an internal geometry can also account for other psychophysical aspects of vis­ ual perception. For one point, I have already noted that such an analysis predicts the presence of discontinuities in visual space when there are sharp discontinuities in the depth function for rela­ tively close objects, and these discontinuities would seem to be cap­ able of explaining the phenomenon of seeing an “edge” when one relatively close physical object partially occludes the view of another. While there may be more to the “edge” phenomenon in some cases, such as when color contrast is involved, the fact that “edges” are clearly distinguishable when an object is seen against a qualitatively identical background, as with the case of many of Julesz’ random dot stereograms,26 shows that it also involves a geometric property, such as the one which I have just explicated. Certain optical illusions can also be explained by the foregoing account. For instance, consider the Muller-Lyer illusion, where the center line of the figure^— ■Cs seen as being longer than the center line of the figure . It can be noted that certain

113

perspective visual depth cues are contained in the figures; with these cues pointing towards the center line being more distant than its background in the first figure, and closer than its background in the second figure. Since an object that subtends a given visual angle will be constructed larger in visual space the more distant it is perceived to be, due to the nature of Equation 3.14, the illusion is then explained. Similarly, the moon illusion (the fact that the moon appears larger when seen on the horizon than when it is seen directly overhead) can be explained by means of an analogous rati­ onale, once it is noted that there are more visual depth cues present, notably textural ones present in the surrounding background, when it is seen near the horizon than when it is seen overhead. Another phenomenal characteristic of vision which the theory seems to be at least potentially capable of explaining is the tendency towards shape constancy; that is, the tendency for the visual shapes of objects seen at to the shapes projected when these objects are seen head-on. For example, a circular object seen at a slant will appear less elliptical than its central projection onto the retina, but not circular either, as Robert Thouless describes as follows:

If a subject is shown an inclined circle and is asked to select from a number of figures the one which represents the shape seen by him, he chooses without hesitation an ellipse. This ellipse, however, is widely different from the one which repres­ ents the shape of the inclined circle indicated by perspective, being much nearer to the circular form. The subject sees an inclined figure neither in its ‘real’ shape nor in the shape which is its perspective projection but as a compromise between these. (20) Much recent work has been performed in investigating the shape constancy tendency, and while, as with size constancy, much has been found to depend on instructions and the subsequent attitude of the subject, findings for “projective instructions” (which I discussed earlier with my treatment of size constancy) have in general sup­ ported Thouless’ conclusions. I will now show how my variable curvature theory of visual space can at least in principle explain this tendency towards shape con­ stancy. The main point to be made here is that if an object is seen at a slant, then one edge of it must be nearer to the viewer than the other edge, and thus both q and q will possess different values for these

114

two edges, and the object will be constituted in visual space at a slant also. However, due to the inverse nature of Equation 3.21 relating e to q' , the area of the object as constituted on this slant in visual space will not be sufficiently great for the object to retain the same shape as when it is seen head-on. Thus, it will instead be perceived at a compromise shape in between that shape and the one given by the laws of perspective, therefore agreeing, at least qualita­ tively, with Thouless’ results. Due to the lack of precision in the data with regard to the extent of the shape constancy tendency, it would seem to be impossible to account for it in a more quantitative fashion at this time. It might also be worth noting here that the tendency towards shape constancy, thus explained in terms of visual space being constituted at a slant, might be responsible for certain distortions away from a linear perspective found in the work of certain artists, the results of which in certain respects look more “realistic” than do similar works in linear perspective. For example, Patrick Heelan27 has attempted to explain a number of the “distortions” in the work of Van Gogh in terms of the Luneburg theory that visual space is hyperbolic. However, it would seem, as I have previously shown, that these distortions could equally well be explained by means of the tendencies towards size and shape constancy in visual space, and our inability to adequately account for these tendencies by means of a rectilinear projection on a flat two-dimensional canvas. I shall now turn to a discussion of how the variable curvature theory can account for the aspect of phenomenal visual depth per­ ception which is enhanced by binocular vision; this being a subject which I promised in Chapter Two to eventually treat. For one point, a discontinuity in visual space (a so-called “edge”) can be noticed, and can serve as a phenomenal cue that there is a physical gap between the corresponding physical objects being seen; i. e., that one partially occludes the view of the other. Another, and probably more significant, phenomenal visual depth cue arises from the fact that one can apprehend, to at least some extent, the internal metric structure of visual space, as, for example, by noticing the presence of a corner or the presence of convexity or concavity in visual space. Visual space does not appear as being flat when the objects consti­ tuted in it possess different physical depths, and one can use this “lack of flatness,” that is the apprehension of an internal curvature, as a phenomenal visual cue for depth. H. H. Price took note of this

115

aspect of visual perception in the following passage from his book Perception. This visual sphere, as we may call it is something that we carry about with us whenever our eyes are open. It plays the same sort of part as our skin does in touch. Only it is, so to say, much more plastic than our skin: it expands to great size, and again contracts and it modifies its interior into various shapes. Its inside surfaces are always taken to be the outside surfaces of objects, and to be so taken is its function or end. (21) The question arises at this point as to how the phenomenal visual depth cues just noted are enhanced by means of the binocular physi­ ological depth cue of retinal disparity. In order to answer this ques­ tion, it can first be noted that the tendencies towards both size and shape constancy are greater under binocular vision than they are monocularly. For instance, Boring, Edwin and Taylor,28 Chal­ mers,29 and Ueno30 have shown that monocular size constancy experiments yield results which are closer to a null match than do binocular experiments. Similarly, Thouless^l has shown that visu­ ally perceived shape is closer to the shape projected onto the retina in monocular vision than it is binocularly, and this effect can be readily confirmed by closing one eye, and then seeing how the shape of a given object constituted in visual space changes. It can also be noted that the field of view of binocular vision is somewhat wider than that of monocular vision (at least partially because the pres­ ence of the nose imposes an artificial boundary on the monocular field), and that even taking the foregoing differences in size con­ stancy into account, objects are still often seen somewhat smaller under monocular vision than binocularly. There seems to be a fair amount of variance among different individuals with respect to the magnitude of this latter effect though, and for some the effect may be the reverse of that just noted. William James, for example, took note of this last effect as follows: This page looks much smaller to the reader if he closes one eye than if both eyes are open. So does the moon, which latter fact shows that the phenomenon has nothing to do with parallax. (22) It would seem then that the binocular physiological depth cue of retinal disparity enhances monocular phenomenal visual depth

116

effects by means of changing the values of the constants in Formula 3.21: q

= C - 1/aQ

C changes inasmuch as even the sizes of very distant objects, such as the moon, are changed binocularly (although as I noted the degree of change varies among individuals), and a (a personal pro­ portionality constant) increases binocularly, accounting for the changes in size and shape constancy. Thus, due to this enhance­ ment in binocular vision of the effects of the depth function/fe, t) on the metric structure of visual space, that structure can be more readily apprehended phenomenally, resulting in enhanced pheno­ menal visual depth perception.

CHAPTER FOUR VISUAL ORIENTATION, PHENOMENAL SPACE, REGRESSES AND OUTNESS The notion that we see our retinal images is based on some such idea as a little seer sitting in the brain and looking at them. The question which then arises is how he can see. J. J. Gibson

This chapter deals with a mixture of subjects which are only loosely related to each other; these being respectively orientation problems concerning vision, the geometry of phenomenal space, the “eye regress,” and the sense of “outness” of our percepts. These subjects all constitute prerequisites to my analysis of the mind body problem in Chapter Five though, and as will become evident, there are cer­ tain interconnections among them. I shall begin the chapter with an analysis of certain puzzles concerning visual orientation, most not­ ably the problem of how objects constituted in visual space can appear to remain stationary during head and eye movements. My discussion of this problem will lead into an analysis of the concept of a space of potentialities. In this section I shall also discuss break­ downs in the orientation system, notably ones which result in the whirling sensation of vertigo. My next section will consist of an extension of my investigation of the geometry of visual space to also include an analysis of the geometry of “phenomenal space;” that being an all encompassing space of each of the different senses, only one portion of which being comprised of visual space. I will first investigate the spatial charac­ teristics of the respective senses of audition and touch separately, and will then show how the percepts corresponding to these senses can be integrated together with visual ones in the overall pheno­ menal space. N ext, I shall deal with a series of arguments claiming that various regresses occur in the account which I have been giving of the

118

nature of perception. I call these “eye regress” arguments; one prim­ itive version holding that there is a regress of actual eyes in visual perception, in that another eye would be required in order to see the retinal image of the first eye and so on. I will distinguish a number of different variations on this regress argument at different stages of the perception process, including a phenomenal regress argument which claims that another percept is required in order to “see” a first one, and so on. My discussion of this regress will tie in closely with my final section on the sense of “outness” of phenomenal space, since I will show there how percepts in phenomenal space can be conceptually referred to without any actual duplication of the per­ cepts involved taking place. I shall argue that each variation on the “eye regress” argument fails inasmuch as once a certain phase in the perception process has been accomplished, there is no need for it to be repeated, and thus that no regresses need develop. Finally, I shall investigate the sense of “outness” of phenomenal space, this'being the sense; for example, in the case of visual space, that visual percepts are sensed as being located out away from “us.” This investigation will lead into digressions into both the nature of the “self which “sees” events in phenomenal space, and also, as just noted, into the nature of conceptual reference.

119

4.1 Visual Orientation In this section I shall undertake a geometric analysis of certain aspects of the phenomenology of visual orientation; i. e., the aspect of our visual experience whereby the positions of objects constituted in visual space seem to be independent of both eye and head move­ ments. In other words, I shall analyze how objects constituted in visual space can be experienced as remaining stationary even though the optical projections of these objects onto the retina changes. It will be necessary to analyze the concept of a “space of potentialities” prior to undertaking this analysis in detail. When we turn our head while viewing a given object, the object as constituted in visual space is not experienced as moving also (i. e., it appears to be stationary), even though it changes its position in visual space as I have geometrically characterized that space pre­ viously; that is, the constituted object will move either closer to or further away from the boundaries of the space. The constituted object may even recede from visual space altogether if we turn our head far enough, in which case we say that we no longer “see” the given object. A related point, to be expanded on in my next chapter, concerns the fact that we are usually subjectively unaware of our eye movements, especially the small periodic ones called “saccades.” This shows that specific points of visual space are not correlated with specific points on the retina, since these latter points undergo an almost continuous motion, which possesses no phenomenal correlate. It can also be noted that this property of the non-motion of objects constituted in visual space sometimes breaks down, such as during the subjective whirling experience of vertigo. There are two different types of vertigo—subjective vertigo, where the subject experiences himself as rotating while visual space remains stable—and objec­ tive vertigo, where visual space itself is experienced as rotating. This latter experience is the reverse of the one just analyzed where objects constituted in visual space remain stationary in spite of head movements, since, in objective vertigo, these objects seem to be rotating even if we remain facing in one direction. There are many different causes for vertigo, including the relatively rapid rotation of the body and disturbances of the vestibular system, notably ones involving the inner ear. Inasmuch as my explication of the just noted phenomena con­ cerning visual orientation will involve the integral use of the con-

120

cept of a “space of potentialities,” I will begin with an analysis of that subject. The concept of “potentiality” as it is ordinarily made use of is rather vague, and it also possesses a number of distinct more specialized uses. Thus, it is important to be clear as to which meaning is being used at any particular time. Whitehead, for exam­ ple, took note of this ambiguity in a somewhat different context in the following passage from Process and Reality.

Thus we have always to consider two meanings of potential­ ity: (a) the ‘general’ potentiality, which is the bundle of possibili­ ties, mutually consistent or alternative, provided by the multi­ plicity of eternal objects, and (b) the ‘real’ potentiality, which is conditioned by the data provided by the actual world, (p. 65) As Whitehead points out, one of the senses of “potentiality” refers to the merely logically possible, in which case any non-contradictory state of affairs is said to be “potential.” This sense of potentiality is much too broad for use in the context under consideration here, inasmuch as many logical possibilities are neither physically pos­ sible nor phenomenally possible (two concepts which I shall now discuss). A somewhat stronger sense of the potential refers to the physi­ cally possible; i. e., a state of affairs which is in accordance with the laws of physics. I analyzed this sense in Chapter One in my section on physical causation, and, inasmuch as it applies to physical events, it would not seem, prima facie, to also be applicable to the mental phenomena currently under consideration. A related sense of potentiality which is more relevant to the present concern is that of the phenomenally possible. This sense refers to a state of affairs being in accordance with the laws of phenomenology; the visual geometric laws of which having been analyzed in the last two chap­ ters. This last sense of potentiality is the one which I made use of in my interpretation of the Luneburg theory as referring to a threedimensional space of potentialities; the space being held to be poten­ tial in the sense that each of its points are potentially capable of being occupied by visual percepts, even though each one is usually not so occupied. In fact, nothing at all need exist in such a space; it is just the case that it is phenomenally possible for regions of the space to be occupied by the relevant percepts. There is still another sense of “potentiality,” which Whitehead alluded to in the quoted passage, in which the potential is used in

121

contrast with the actual (here being the phenomenally actual), into which it is held to be capable of being transformed. Thus, in this sense, and in contrast to the sense which I made use of in my interpretation of the Luneburg theory, the space of potentialities will exist, although in this case its mode of existence will not possess a phenomenal format. The space will still presumably possess a rudimentary “mental” character though, although it would not seem to be possible to characterize this format in a more positive manner, inasmuch as we are never phenomenally aware of it. A space of potentialities, in this sense, possesses the “potency” to become phenomenal, or, put in another way, a phenomenal mode of existence is “latent” in it. I shall not enter into a more detailed analysis of these matters in this book, and readers are referred to Whitehead’s Process and Reality for a more detailed discussion. I shall now turn to my analysis of how a space of potentialities, in the last sense analyzed, can elucidate the visual orientation pheno­ mena which I discussed at the beginning of this section. My basic claim here is that visual space, as it has been previously character­ ized geometrically, is capable of “motion” with respect to a space of potentialities as just defined. In particular, the claim is both that under normal circumstances (i. e., in the absence of vertigo), points of the space of potentialities will be aligned with specific directions in our physical environment, and also that visual space can change its position with respect to this space of potentialities by, in effect revolving with respect to it. The concept of the “motion” of visual space with respect to a space of potentialities needs to be clarified here. If it was meant literally, nothing would be explained, inasmuch as we are never (by defini­ tion) aware of the points of the space of potentialities, and thus we would not be aware that anything was moving with respect to them. However, this “motion” can also be interpreted as meaning that when visual space, as it has been previously characterized geomet­ rically, “moves” with respect to the space of potentialities (as when we turn our head), the points of visual space themselves do not actually move, but instead either recede from a state of actuality to one of potentiality or accede from a state of potentiality to one of actuality along the line of motion. Inasmuch as under this interpre­ tation the points of visual space themselves will always remain stationary with respect to the space of potentiality, with only the sets of points which are actualized (and which we are thus visually

122

aware of) changing during head motions, it follows that objects constituted in visual space will remain stationary during these motions. A useful analogy to bring in here is that of a rotating spotlight. Stationary objects along the beam of the spotlight will alternate from a state of being illuminated to a state of being unilluminated as the light beam passes over them. The objects themselves do not move during this process, even though the region of illumination does move. Thus, the region of illumination can be taken to corres­ pond to actualized visual space, and the non-moving objects can be taken to correspond to the phenomenal objects constituted in visual space, which alternativelj' are actualized (illuminated) or recede into potentiality (are unilluminated) during head and eye motions. The whirling sensations of vertigo can also be explained now. The sensation of rotation here will be caused by the “movement” of visual space, only in this case including the objects constituted in it, by means of its receding from and acceding to potentiality as just explained. That is, the visually constituted objects will no longer be stationary with respect to the space of potentialities, but instead will “move” along with actualized visual space with respect to it. I shall now turn to a discussion of how sensations corresponding to the other senses can be mapped onto one common phenomenal space which includes visual space. As in my account of the orienta­ tion of visual space, the concept of potentiality will play a major role in this discussion as well.

123 4.2 The Geometry of Phenomenal Space

In this section I shall analyze the geometry of phenomenal space; that being an overall space of all the different senses, only one portion of which being comprised of visual space. Compared with the case of vision, there is very little literature on the phenomenal spatial characteristics of the other senses, and indeed it will turn out that these spatial characteristics are only vaguely apprehended in comparison with the visual sense. In fact, the spatial properties of the “chemical senses” of smell and taste are so vague (this is in no way meant to imply that they are non-existent though) as to be incapable of analysis, other than to say that thereis a vague sense of direction associated with them. However, it is possible to analyze the phenomenal geometry in some detail for the respective senses of audition and touch, although even here the precision of analysis which is possible is nowhere near that of the visual case. One way in which the phenomenal spaces associated with audi­ tion and touch differ from visual space is that they usually exist in a potential mode, with portions of them only becoming actualized (consisting of conscious percepts) when there are either appropriate stimuli in the environment or during appropriate mental imagery (which is a subj ect matter which I shall not deal with in this book).l In contrast, in the visual case, in the absence of light stimulation from a section of the environment, we sense the phenomenal color of black, and in fact a black visual field is also present when we close our eyes. In spite of this difference between visual space and the other sensory spaces, I shall argue that they are still spatially coordinated together. I shall now turn to an analysis of the respec­ tive geometries of auditory space and somatic space; first separ­ ately, and then as integrated together with visual space in one common overall phenomenal space. Auditory Space There is a sense of direction associated with audition, as is evi­ denced by the fact that we can at least usually tell the direction in which a sound is heard, and there also seems to be some sort of a sense of auditory depth, although this latter feature is much more vague than the sense of direction. The chief physiological cue for the sense of direction in audition involves the degree of “out of phaseness” of sound waves in the air when they impinge upon the respec-

124

Figure 4-1

tive ear drums of the two ears. The time difference between when these sound waves strike the ear drums is a function of the direction of the source of the sound, as can be derived from Figure 4.1, where S represents the source of the sound, L represents the left ear drum, and R represents the right ear drum. The direction of the source of the sound from a position halfway between the two ears can then be derived by noting that:

cosd

(a~b)/c

(4.1)

and thus the time difference between when the sound waves strike the respective ear drums, which is directly proportional to| a~b |,will determine the direction of the source of the sound with respect to a plane containing the two ears. As is evident from this discussion, there is an ambiguity in this physiological cue as to whether the source of the sound is overhead or beneath one, inasmuch as the time difference will be the same in both of these cases. There are additional physiological cues which are called into play here though, notably ones involving the impact of sound waves on the

125

outer ear, but still there is sometimes a phenomenal difficulty in distinguishing between the two cases. I shall now turn to my discussion of the actual geometry of audi­ tory space. While there is a moderately precise sense of direction experienced with phenomenal sounds, this phenomenal direction is not always accurately coordinated with the direction of the physical source of the sound. For example, in Chapter One I took note of the cases of viewing a movie or a television show, where the sounds seem to be coming from the actors’ mouths, while their physical source is with a speaker which may lie at a considerable distance away. This effect also takes place in ventriloquism, where the suc­ cess of the ventriloquist in “throwing” his voice is at least partially due to the synchronization of the facial movements of the “dummy” with the words being said. Compared with vision, there is relatively little spatial acuity in auditory space, as is witnessed by the fact that it is difficult to phenomenally attend to more than two different sounds at once; a poignant example of which (although opposite to the point of a phenomenon often referred to as the “cocktail party phenomenon” that we can often pick out a single voice at such a party) is consti­ tuted by talk at a cocktail party, where the various voices seem to merge together and are heard as sort of a buzz. Mach, for example, took note of this lack of phenomenal auditory spatial acuity as follows: Similarly, the determination of position in space by means of the ear is far more uncertain and is restricted to a much more limited field than by the eye. (Space and Geometry, p. 15) It is difficult to tell whether this lack of spatial acuity in auditory space is due to physiological difficulties in separating out the var­ ious components of sound waves originating from different sources, or to a primitive fact about the spatial resolvability of auditory space. It should be noted though that the former problem is a very difficult one for cases involving more than two or three different sources. With regard to the topology of auditory space, it can first be noted that the space is unbounded inasmuch as we can hear sounds in any given direction, including behind our head, and in this respect the topology of auditory space differs from that of visual space, which I have previously noted possesses a limited field of view. It is difficult

126

to determine the dimensionality of auditory space directly by means of introspection, but I shall later show that there are considerations from the general overall phenomenal space which make the possi­ bility that this format is two-dimensional extremely attractive. Phenomenal auditory depth perception is quite weak, even though there may be a sufficient amount of physiological information available to make it theoretically possible, and it also seems to be doubtful as to whether we can hear phenomenal sounds as being located behind other sounds. There is even a question in cases where auditory stimuli are spatially spread out or separated, as to whether the corresponding phenomenal percepts are similarly spread out or separated, inasmuch as it may be impossible to distinguish between the two cases by means of introspection. Due to this weakness of introspective evidence, it would seem that there is no direct way to determine the metric structure of auditory space, although, as in the case of vision, it may possess a variable curvature in order to account for what phenomenal auditory depth perception does exist. I shall now turn to my discussion of the geometry of somatic space. Somatic Space

We are phenomenally aware of our body as taking up space, and in fact can localize the various sensations associated with touch—heat and cold, pain, kinesthetic percepts, etc.—as being located in var­ ious parts of the body. Merleau-Ponty described this somatic space of the body, or “body image,” in great detail in his various works on phenomenology,2 as in the following passage from Signs.

I have a rigorous awareness of the bearing of my gestures or if the spatiality of my body which allows me to maintain relation­ ships with the world without thematically representing to myself the objects I am going to grasp or the relationships of size between my body and the avenues offered to me by the world. On the condition that I do not reflect expressly upon it, my con­ sciousness of my body immediately signifies a certain landscape about me, that of my fingers a certain fibrous or grainy style of the object, (p. 89) The fact that we are spatially aware of our body does not entail that the shape of somatic space is itself spatially isomorphic with the shape of the body though. In fact, there would seem to be grave difficulties with such a position, inasmuch as tactile percepts asso-

127 ciated with our limbs, for example, seem to change their locations with respect to an overall phenomenal space when we bend or oth­ erwise move these limbs, while the distances along the physical body would not change in these cases. It would seem then that tactile percepts are sensed in an overall somatic space not necessar­ ily corresponding to the shape of the physical body, as MerleauPonty points out as follows:

No, my two hands touch the same things because they are the hands of one same body. And yet each of them has its own tactile experience. If nonetheless they have to do with one sole tangible, it is because there exists a very peculiar relation from one to the other, across the corporeal space—like that holding between my two eyes—making of my hands one sole organ of experience, as it makes of my two eyes the channels of one sole Cyclopean vision. (The Visible and the Invisible, p. 141)

I shall now turn to my discussion of the topological and metric structure of somatic space. It is clear that somatic space, like audi­ tory space but unlike visual space, is unbounded, inasmuch as we can sense tactile percepts in any given direction under appropriate corporeal stimulation. However, unlike the case of audition, part of my body must be located in an appropriate direction (with the excep­ tion of the “phantom limb” phenomenon, where tactile percepts seem to be still felt in our limbs after the physical limbs have been amputated) in order for these percepts to occur in any given direction. In contrast to the issue of its boundedness, there has been a fair amount of controversy regarding the dimensionality of somatic space. Berkeley ,3 for example, thought that our sense of depth was derived from touch, which he thought was three-dimensional, while he held that visual space itself was only two-dimensional. This issue of the relationship between phenomenal depth perception and touch sparked a subsequent debate within the Empiricist movement, with T. K. Abbott in Sight and Touch, for example, arguing against Berkeley by noting that we sense visual depth with respect to objects which we never come even close to touching, and also by pointing out that the spatial characteristics of tactile percepts are considera­ bly more vague than those associated with vision. It can also be noted in this regard that I have previously shown how visual depth perception arises from the internal metric structure of visual space

128 itself, and thus it would seem that Berkeley was wrong in his claim that the sense of depth arises from touch. Also, as with the case of audition, I shall argue shortly that there are powerful considera­ tions from the makeup of an overall phenomenal space which point towards tactile percepts being spatially only two-dimensional. As with auditory space, there is little spatial acuity in somatic space, as is evidenced by the fact that it is difficult to tell whether two tactile percepts are in fact separate from each other or just one large percept, and there are also difficulties in sensing one tactile sensation as being located behind another one. However, inasmuch as we are capable of sensing at least the relative depths of tactile percepts (a sensation in my foot seems to be further away than one in my nose), one might have to postulate an internal metric structure to somatic space in order to account for this depth perception with respect to percepts located in it. The spatial acuity of somatic space is much too limited for the precise nature of any such metric struc­ ture to be determined, at least directly by means of introspection, though. I shall now turn to a discussion of how sensations located in the different sensory spaces—visual space, auditory space, and somatic space—are integrated together in one common phenomenal space.

Phenomenal Space There have historically been a number of disputes with regard to the question of how the various sensory spaces are coordinated togeth­ er, particularly concerning correlations between sight and touch. For example, certain of the British Empiricists, notably Locke4 and Berkeley,5 were concerned with a problem posed by William Moly­ neux as to whether someone born blind with cataracts, after being “couched” (having the cataracts removed) would correlate his pre­ vious tactile experience with his newly received visual experience, as by being able to distinguish a cube from a sphere visually afterhaving previously been taught the distinction by touch. Both Locke and Berkeley gave a negative answer to Molyneux here, and Berke­ ley even argued that visual experience is entirely separate from tactile experience; e. g., that we in fact are seeing and touching different objects even when they are verbally identified as being the same. While experimental results at the time were taken to confirm Locke and Berkeley on this point, recent experiments6 along the same line suggest that this result may be merely due to an initial

129

confusion on the part of the subject immmediately after the cataract operation and in a deficit in his ability to verbally describe the newfound visual experience, rather than being due to a primitive fact concerning the separateness of visual and tactile experience. Dr. Johnson’s purported refutation of Berkeley’s immaterialism by means of kicking a stone also deserves mention here, even though it does not show, as Dr. Johnson thought, that naive realism is correct, but merely that tactile experience is spatially correlated with visual experience. In fact, it does seem to be clear introspectively that the different sensory spaces are spatially correlated together, inasmuch as when I both see and feel or both see and hear the “same object,” the percepts correlated with these different senses seem to be located in the same place. Thus, it would seem to be worthwhile at this point to postulate the existence of one common sensorial space, “pheno­ menal space,” wherein percepts from the different sensory spaces are integrated together. I shall now attempt to account for this sensory integration in terms of the geometric structure of pheno­ menal space. Two claims here are that phenomenal space is topolog­ ically two-dimensional and that it globally possesses a spherical metric structure. The specific locations of particular sensations on this phenomenal sphere would then be held to be correlated with the directions in which the sensations are sensed; that is, for example, with visual angles subtended by objects being viewed being directly correlated with spherical angles on the phenomenal sphere. Thus, visual space would occupy somewhat less than a hemisphere on the phenomenal sphere, corresponding to its 170° of horizontal width and 120° of vertical width. Similarly, if something is both seen and heard in the same direction, the percepts corresponding to these senses would occupy the same locations in phenomenal space. It would also follow that if one should move a limb, the tactile and kinesthetic percepts corresponding to it would change in position in phenomenal space, in accordance with the direction which it moves in. Inasmuch as the percepts from the different sensory systems are all being treated as being topologically two-dimensional here, one might even have to postulate an “onion peel” arrangement for phenomenal space in order to explicate cases where one percept is sensed as being located behind another one. Possibly this type of analysis could be carried even further by the use of polar coordinates

130 and differential geometry in order to simulate depth, as I did with the visual case, but I shall not attempt such a more detailed geomet­ ric analysis here in view of the spatial acuity problem for the senses other than vision previously noted. It should also be emphasized that, as in the cases for the spaces for the individual sensory modes (visual space, auditory space, somatic space), phenomenal space will be a space of potentialities, with sections of it only becoming actualized in a particular sensory mode under appropriate stimulation; e. g. in normal cases when there is appropriate stimulation from the corresponding direction in the environment. I shall now turn to my section on the “eye regress,” and show there for the particular case of visual perception, although similar remarks could be made with respect to the other sensory systems, that no regresses need develop in the perception process.

131

4.3 The Eye Regress

One persistent criticism of the causal theory of perception has been that it leads to an infinite regress. In the visual case, for example, it has been contended that a second eye is required in order to “see” what a first eye “sees” and so on. I wish to show that a number of different possible arguments are being lumped together here, and that the failure to distinguish among them at least contributes to whatever initial plausibility the foregoing argument may seem to possess. I shall go on to show that each of these different possible variations fail, inasmuch as they at the most only demonstrate the presence of finite regresses in the perception process, and fail to take into account the fact that once a certain facet of the perception process has been accomplished, there is no need for it to be repeated, hence circumventing the need for infinite regresses. I shall now turn to a discussion concerning the different possible variations on the perceptual regress argument, by way of investigating several differ­ ent historical versions of the argument. Perceptual regress arguments seem to have been originated by Descartes,7 and variations on them have been raised by a large number of philosophers and psychologists since then, including Gilbert Ryle,8 D. M. Armstrong^ and J. J. Gibson.1° A family of different regress arguments have been raised here, ranging from the claim that there is a regress in the need for actual eyes (in the literal sense of containing a lens for focusing light) in visual perception, in that another eye is needed in order to “see” the first eye’s retinal image and so on, to the claim that a regress develops in the need to “see” one’s visual percepts, in that a separate percept is needed in order to “see” the first one, and so on. Not all of these regress arguments have been restricted to the visual sense, as, for example, there have also been claims that regresses result from the positing of “body images” or “humunculi” in accounts of the perception of touch. However, I shall only discuss purported visual regresses here, but it can be noted that analogous remarks apply to regress argu­ ments involving the other senses. Descartes raised his version of the eye regress argument as fol­ lows in the Sixth Discourse of his Optics:

Now although this picture, in being so transmitted into our head, always retains some resemblance to the objects from which it proceeds, nevertheless, as I have already shown, we

132

must not hold that it is by means of this resemblance that the picture causes us to perceive the objects, as if there were yet other eyes in our brain with which we could apprehend it. (p. 101) Descartes raises the problem here as to how a physical resemblance between our retinal images and objects being seen could possibly account for visual perception, noting that this cannot be done by means of other eyes, since that would lead to an infinite regress. Thus, Descartes is not so much criticizing the causal theory of perception (a version of which he endorsed)! 1 here, as pointing out that it must appeal to something more than the resemblance between an image and the physical objects constituted in the image, in order to account for the perception of the physical object in ques­ tion. I shall discuss the mind body ramifications of this issue in my next chapter, and thus will just investigate here the question of whether or not a regress of eyes, in the literal sense of optical systems, need actually develop in order for an image to be trans­ ferred from one location in the brain to another. For example, D. M. Armstrong in the following passage, where he criticizes Berkeley’s argument that visual depth is not immediately seen, inasmuch as it is projected as only one point on the retina, claims that such a literal eye would be necessary for this purpose. Now granting it to be true that there is only one point projected on the ‘fund of the eye’ (the retina), whatever the distance, why does this show we cannot immediately see the distance? Why does the fact that the projection on the retina is merely twodimensional prove that we cannot see three dimensions? The argument seems to be valid only if we assume that the imme­ diate object of sight is the fund of the eye. But this is obviously false. In the first place, when we see we never see the fund of the eye (although we might see it reflected in a mirror), rather it is objects beyond our eye that we see. In the second place, suppose it were true that the fund of the eye was the object immediately seen. Would we need another eye to see the fund of the eye? After all seeing requires eyes. Butthen, by parity of reasoning, all that would be immediately seen would be the fund of the second eye, which would have to be observed by a third eye, and so indefi­ nitely. (Berkeley’s Theory of Vision, p. 213)

Two distinct criticisms can be made with respect to Armstrong’s arguments in the preceding passage. For one point, even though Armstrong is correct in his claim that we do not, except in bizarre

133 cases, actually see the retina of the eye, it is also the case (assuming that he is using the word “see” in its ordinary English sense) that he is implicitly assuming a naive realist metaphysics in his claim that we see “objects beyond our eye,” and I have demonstrated the falsity of such a metaphysics in my first chapter. A second criticism con­ cerns the question of whether or not Armstrong is correct in his assertion that all seeing requires eyes, in the literal sense of requir­ ing the use of a lens to focus light rays, or some analogue of light rays, upon a two-dimensional surface, such as the retina. It is diffi­ cult to see the point of postulating a second eye here, once the first eye has performed its function of focusing light cones on the retina, and thus converted angular information (the respective sizes of the solid angles subtended by the light cones from the various objects being “seen”) into spatial information (the respective areas on the retina upon which the foregoing light cones are focused). There is no need for a second eye to refocus the light, since that task has been accomplished by the first eye, and thus I can see no danger of a regress developing at this point, although of course there is more to the visual perception process, as I shall discuss in my next chapter. It should be emphasized though that information can still be transferred from the retina to another structure of the brain, by means of nerves connecting corresponding parts of the two struc­ tures, but no lens, and thus literally no eye, is required in this process. By way of analogy, it can be pointed out that in a television camera wires carry signals from the photoreceptors of the camera tc other areas where the information is converted into a different format, with no lens being required in this transferring operation. Gary Thrane makes a number of these same points in the following passage criticizing Armstrong.

If Berkeley’s views are to be saved from Armstrong’s interpre­ tation (which involves the allegation of incoherency), it must be argued that it is false that all seeing requires eyes. This may seem a reductio ad absurdum, but it is not. What is the function of the lens mechanism? By means of it a focused image is pro­ jected on the retina. So far as we know the only biological solu­ tion to the problem of discriminating sight involves the forma­ tion of images by crystalline lenses. Once the image is formed, however, what else is requisite to seeing? A sensitive retina and a working optic nerve. Consequently, although the entire mech­ anism of the eye is requisite to see distant objects, seeing the

134 pattern of light on the retina does not require another eye. The retina, or ‘fund of the eye,’ just is the photosensitive surface. (Thrane, 1977, p. 256)

Thus, it would seem that literally speaking, no further eyes are required in visual perception, once an optical image has been focused on the retina. However, if following the formation of the retinal image, all that follows in the visual perception process in the brain is a series of physical operations on the information from the retina, then a variant on the literal “eye regress” still has some force; that being that even while literally speaking no further eyes are needed to act on the various nerve impulses from the photorecep­ tors of the retina, the problem remains of accounting for how any physical operations of the brain could result in the phenomenal act of seeing. In fact, the question can even be raised here as to what purpose would be served by further physical operations transferring retinal images to various structures in the brain, aside from such processing of these images as is required, for example, to combine the two retinal images for stereoscopic vision. Thus, the classical mind body problem arises at this point as to how any neural state associated with any physical brain structure, regardless of whether this state involves some sort of image or anything else, could contribute to the causal determination of events (e. g., qualitative changes such as color changes, or geometric changes such as those outlined in Chapter Three) in visual space, and this would seem to be the major problem which Descartes was concerned with in the passage quoted from his “Optics.” I shall discuss ways in which this causal “leap” from physical neural states of the brain to events in phenomenal space might take place in my next chapter, and so for now it need only be noted that once such a “leap” has in fact taken place, nothing is gained by repeating it, and thus the physiological regress under discussion will be avoided. There is one final regress which is sometimes held to occur in visual perception; this being a phenomenal regress, where if is argued that another phenomenal percept is required in order to “see” or get “a glimpse of’ events in visual space. Gilbert Ryle, for example, makes this argument as follows:

The theory says that when a person has a visual sensation, on the occasion, for example, of getting a glimpse of a horse-race,

135

his having this sensation consists of his finding or intuiting a sensum, namely a patchwork of colours. This means that having a glimpse of a horse-race is explained in terms of having a glimpse of something else, the patch work of colours. But if hav­ ing a glimpse of a horse-race entails having at least one appro­ priate sensation, which in its turn must be analyzed into the sensing of yet an earlier sensum, and so on forever. At each move having a sensation is construed as a sort of espying of a particu­ lar something, often gravely called “a sensible object,” and at each move this espying must involve having a sensation. (Con­ cept of Mind, p. 213)

I believe that Ryle’s argument here is invalid, and that the fallacy lies in the claim that having a glimpse of a sensation involves having a separate sensation from the original sensation itself, thus allowing for a phenomenal regress to develop. But why is a separate sensation required here? The existence of the first sensation would seem to be sufficient to constitute visual perception, and thus the postulation of further “glimpses” of that sensation would seem to be entirely gratuitous. Due to the very phenomenal character of visual space, something else is not required in order to see it, since seeing is nothing more than the very continued existence of that space; that is to say, the occurrence of events in visual space constitutes the end result of the visual perception process. Of course, events in visual space can still be conceptually referred to—as, for example, with words—but even though I am not sure what the proper analysis of this conceptual reference is, it does seem to be clear that it does not involve a repetition of the visual percepts being referred to, and thus there is no reason to think that a pheno­ menal regress will develop on this point. It should also be empha­ sized that the word “I,” as used in “I see” for example, is used merely in the sense of a grammatical subject, and is not meant to imply the existence of something separate from visual space which is required in order for the act of seeing to take place. Hume, for example, addressed this last point in the following famous passage from his Treatise of Human Nature: For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can observe anything but the perception, (p. 252)

136 Thus, Hume argued that something else is not required in order for perception to take place over and above the existence of the relevant percepts. However, while I agree with Hume on this point, I would not use it, as he did, as an argument against the existence of the mind, since I have shown by my refutation of naive realism in Chapter One, that the space of these percepts is mental. In my next section, I shall also argue that there is a sense in which a “self,” which transcends at least perceptual sensations, also exists. This “self will not be as mysterious in nature as the one which Hume was arguing against, though. It would seem then that the “eye regress” fails at all levels; e. g., in the need for further literal eyes to focus an image, in the need for an indefinite series of physical operations on nerve impulses from the retina, and in the need for “glimpses” of visual sensations. Each phase in the visual perception process serves a particular function, whether to focus light as in the eye, to combine neural signals from the two retinas for binocular vision, or to causally determine the nature of events in phenomenal visual space. But once any of these operations has been accomplished, there is no need for it to be repeated, and thus there is no need for a regress in “eyes” to occur. Having thus dealt with the eye regress, I shall now close the chapter with a short section on the sense of “outness” of phenomenal space.

137 4.4 Outness and the “Self’

In this section I shall investigate the sense of “outness” of pheno­ menal space; that being the sense in which percepts corresponding to the various sensory systems are experienced as being located out away from “us.” For example, in the visual case we project visual space as being located outside of our heads. We definitely experience “ourself as being located in front of visual space, rather than as being located behind it (this effect can be particularly striking when viewing a vast expanse as from a mountaintop or from an airplane), and this asymmetry deserves an explanation. Sherrington, for example, took note of this sense of outness as follows”

The self “sees” the sun; it senses a two-dimensional disk of brightness, located in the “sky,” this last a field of lesser bright­ ness, and overhead shaped as a rather flattened dome, caping the self, and a hundred other visual things as well. Of hint that this scene is in the head there is none. Vision is saturated with this strange property, called “projection,” the unargued infer­ ence that what it sees is at a “distance,” from the seeing “self.” (Integrative Action of the Nervous System, pp. xvi, xvii) Berkeley attempted to explain this sense of “outness” of visual percepts in terms of associations with the sense of touch.12 Such an account would seem to be unsatisfactory, both because introspectively the sense seems to be primordial, and since we never come into physical contact with many of the objects being seen, and thus could not have made tactile associations with them. I thus will take the sense of outness of phenomenal space to be innate, and will shortly attempt to account for it in terms of the topologic relationship of phenomenal space with something else, which I shall call the “self,” which is “aware” of this outness. That is to say, in order for the awareness of phenomenal outness to occur, something must exist which “possesses” this awareness, and I am defining this some­ thing as being the “self.” It should be emphasized that nothing mysterious is meant by the “self’ here, and I shall now proceed to analyze what I do mean by it. I will then explicate its topologic relationship with phenomenal space in order to account for the sense of outness. It will be important to avoid any regresses, such as those discussed in the last section, in this analysis. While the concept of the “self’ is sometimes used to refer to our complete consciousness, I am just using it here to refer to that

138

portion of consciousness (I will defend the claim that consciousness can possess spatially separated parts in my next chapter when I discuss the relative merits of Hume’s “bundle theory of the mind” and Kant’s claim that there is a “transcendental unity” to “apper­ ception”), where abstract thought, language, and the will are located. Inasmuch as phenomenal space and the “self’ are both parts of the same conscious space, they can be seen to together constitute just one entity; the act of seeing, per se—as I have expli­ cated earlier—being constituted by the very existence of the visual portion of that space. However, even though the existence of the “self’ is not required in order for the act of seeing per se to take place, the “self’ still has access to information concerning events occurring in visual space, or indeed also to events occurring in other regions of phenomenal space, as is evidenced by its ability to react to events occurring there. Thus, there must be causal connections between the “self’ and the various regions of phenomenal space (although there is no evidence for any direct causal connections between those points which do not involve the “self’), inasmuch as we can both conceptually refer to events occurring in phenomenal space, and also act on this informa­ tion. It might also be noted that this causal connection may well be reciprocal; as for example in visual imagery, events in visual space seem to be caused voluntarily by the will, although of course during veridical perception such a causal connection would not take place. Before I analyze how the sense of outness arises from the topologic relationship between the “self’ and phenomenal space, I shall briefly enter into a phenomenological analysis of how it is possible for the “self’ to conceptually refer to events in phenomenal space. It is evident that this conceptual reference does not entail any actual duplication of the percepts in phenomenal space being referred to by the “self,” inasmuch as such a duplication would result in a pheno­ menal regress such as that discussed in the previous section. Instead, this reference is linguistic, and thus an analysis of how phenomenologically such a linguistic reference can take place is required here. Such an analysis would obviously involve problems in the phenomenology of both meaning and reference, and I am not prepared to enter into a lengthy digression into these matters here. Instead, I will merely point out that at least under normal circum­ stances one portion of such an analysis would have to be made in terms of the phonemes (or sometimes the visual images) constituted

139 by words. Of course, something else is also required for this analysis to work, namely that which comprises the difference between think­ ing of a nonsense syllable and thinking of one with meaning. While it may be possible to carry this analysis further in terms of the various percepts associated with these phonemes, I will let matters stand at this point. I will not digress here into an analysis of the “will” either. Instead, I shall now turn to my discussion of how the topologic relationship of the “self’ in connection with phenomenal space can account for our sense of outness with respect to events in that space. My basic claim here is that the “self’ is located in a threedimensional overall space in which phenomenal space is also embedded. The “self,” from a three-dimensional point of view, will be located in the center of the phenomenal space, by which it will be surrounded. I also wish to claim that there are no direct spatial connections between the “self’ and points in the phenomenal space through the three-dimensional overall space in which both of these are embedded. Instead, I hold that the “self’ and the phenomenal space are only spatially connected along the various interconnected two-dimensional surfaces of the phenomenal space itself (it can be recalled that I postulated in my section on the geometry of pheno­ menal space that that space possesses an “onion peel” like topol­ ogy). Thus, events in the phenomenal space will be sensed as being located out away from the “self’ due to the lack of a direct thirddimensional connection; the intervening points in the three-dimen­ sional overall space not being sensed. It would seem then that the sense of outness of events in phenomenal space can be accounted for in terms of the topologic point that the only phenomenal spatial connections between points of phenomenal space and the “self’ are along the very two-dimensional surfaces of the “onion peel” like phenomenal space itself. This ends my discussion of the spatial phenomenology of the various senses, and I shall now turn to my chapter on the mind body problem.

"■

■

■

CHAPTER FIVE THE MIND BODY PROBLEM There follows on, or attends, that stage of brain-cortex reaction an event or set of events quite inexplicable to us, which both as to themselves and as to the causal tie between them and what preceded them science does not help us; a set of events seemingly incommensurable with any of the events leading up to it. Charles Sherrington

In this chapter I shall investigate the question of how it may be possible for events in phenomenal space to be causally determined by neural events in a region, or series of regions, of the brain. This chapter will be much more controversial and speculative than ear­ lier ones, which to an extent are logically independent of it, but at the same time it deals with an extremely deep philosophical prob­ lem, that of how there can be a mind body causal connection, and this problem should not be ignored. There would seem to be no great philosophical problem in analyzing the physical causal chains of events connecting the physical objects being sensed with events ir the central nervous system, as there my analysis of these chains ir terms of physical necessity or physical probability would seem to suffice. However, unless these physical causal chains of events possess some sort of phenomenal element to them, there would seem to be at least a qualitative "gap” between the resulting physical brain states and events in phenomenal space, as noted by Sherring­ ton in my opening quotation. The problem thus arises as to how any causal gap between a physical state of affairs in the brain, and a phenomenal state of affairs, such as the events in phenomenal space, can be narrowed, or even closed. The extent to which a problem arises here depends upon what constraints are present on causal connections between physi­ cal and phenomenal events, and 1 shall deal with this question in my next section. In the following section I will summarize the neu­ rophysiology of visual perception, and will then speculatively postu­ late a theory claiming that there is a mind body causal connection

142

with various “projection sites” in the cerebral cortex. In the final section I will briefly investigate the relative merits of dualistic ver­ sus dual aspect theories as constituting solutions to the mind body problem.

143 5.1 Constraints on Mind Body Causal Connections In this section I shall investigate what sorts of constraints apply to possible mind body causal connections. Two different types of con­ straints have historically been suggested here; one being a spatial constraint, holding that the physical cause must be spatially con­ tiguous to its phenomenal effect, and the other being a qualitative constraint, holding that there cannot be a sudden qualitative shift between the cause and the effect; that is, the respective modes of existence of the two must be qualitatively comparable. I shall dis­ cuss the spatial constraint in detail shortly, but will first discuss the qualitative constraint. I shall begin this examination of qualitative constraints on causal connections between physical and phenomenal states of affairs by investigating whether or not a sharp qualitative gap in fact exists between the two, and will then investigate the possible consequen­ ces of such a gap existing. Inasmuch as the very phenomenal nature of phenomenal states of affairs themselves constitutes at least one aspect of their qualitative nature, the foregoing question of whether or not there is a qualitative gap between these states of affairs and physical ones reduces to the question of whether physical states of affairs also possess a phenomenal aspect to them. It will turn out that there is little direct evidence which can be cited, one way or another, for deciding this question. One indirect argument for the ascription of phenomenal charac­ teristics to physical states of affairs involves the theory of evolution. This argument first notes that according to evolutionary theory there is a continuity in types of organic existence running from complex organic molecules—to more complex “organisms”—to higher animals—to man. Since man possesses consciousness, it is then argued that these other organisms and complex molecules must in turn also possess a phenomenal aspect to their “minds,” although presumably of a more rudimentary character than the consciousness of man. Thus, a theory could be developed to explain the occurrence of consciousness in man, by postulating its develop­ ment through evolution from a phenomenal element of inert matter. In fact, Whitehead in “Process and Reality,” and such “evolution­ ary epistemologists” as Abner Shimonyl and Donald Campbellhave argued for such a position. Other “dual aspect” theories, along much the same lines as the foregoing ones, postulate the “emergence” of consciousness at some

144 unspecified point along the evolutionary continuum, and thus do not hold that all physical entities possess a phenomenal aspect. The identity theory of Herbert Feigl/i which claims that there is a numerical identity between certain brain states and conscious expe­ rience, belongs to this latter group. It might be noted though that emergent theories would have to postulate a qualitative “jump” at some point on the physical causal chains linking objects being perceived with our phenomenal experiences of them, inasmuch as these theories do not hold that these chains possess a phenomenal aspect to them (they do not postulate in general a positive theory as to what the qualitative nature of these physical causal chains would be either). Thus, they would not differ from dualistic theories on the particular point of the need for such a qualitative jump. While it is true that the possibility of a causal qualitative jump, such as that just discussed, has often been thought to be incoherent (in fact this was one of the prime motivations behind the denial of interactionism by Malebranche-1 and Leibniz^), I do not believe that causality is sufficiently well understood, as yet, that such a possibil­ ity can be ruled out a priori. In fact, it is not clear even that such qualitative jumps do not occur within the realm of physical causal chains, such as when one type of field is converted into another, as in electromagnetism, or when a particle decays by emitting an electromagnetic wave. Of course, this depends upon the ontological nature of the events involved here, which is a subject which is still only poorly understood. It should also he emphasized that it is impossible to directly verify whether or not atoms, or any configura­ tions of them, in fact possess a phenomenal aspect, and thus any theory postulating the development of consciousness through evo­ lution is faced with the other minds problem, which I discussed in Chapter One, of showing positive evidence that it is in fact the case. This problem is more striking for the non-emergent theories of this group, inasmuch as they cannot even appeal directly to the induc­ tive argument by analogy, that inasmuch as I possess conscious­ ness and also share many physical and behavioristic features in common with other living creatures, by analogy these creatures must also possess consciousness. This is because the positive anal­ ogy upon which the foregoing argument depends becomes progres­ sively weaker the further along the evolutionary continuum it is pushed (I possess relatively few physical characteristics in common with an amoeba and fewer still with an atom). It would seem then

145

that the strongest point which can be made in favor of these theories is that there is no obvious “cutoff point” along the evolutionary continuum for separating conscious from non-conscious entities. I shall now turn to a discussion of the second constraint which I postulated as holding for causal connections between physical and phenomenal states of affairs; namely that these states of affairs must be spatially contiguous to each other. This postulated con­ straint lies at the heart of the classic mind body problem of how the mind and brain can causally interact, since classically the mind was held not only not to be spatially extended (I shall later challenge the validity of this claim), but also not even to hold a spatial loca­ tion, and thus it would be impossible for it to be spatially contiguous with even a small region of the brain. The foregoing constraint on the spatial relationships between causes and effects obviously makes mind body causal interactions (with the mind thus defined), to be impossible. This was the classic mind body problem which led some philosophers, such as Malebranche (whose “occasionalism” I have previously noted possessed other motivations as well), to deny the existence of such interactions altogether. I shall later suggest a less drastic manner for getting around this problem, but first I wish to show that one of the premises upon which it rests, the spatial contiguity of cause and effect, has been quite well established in at least the realm of physical causal relationships. According to Hume's*’ analysis of causation, not only must the cause be temporally both contiguous and precedent to its effect, but also the two must be spatially contiguous. Hume was not the origi­ nator of the spatial constraint part of this analysis, since that idea is also present in Descartes’ restriction on physical causal connections to contact action, but in any event such an analysis would seem to be defensible in reference to physical causal relationships. Field theor­ ies, which hold that physical causal chains, such as electromagnetic waves, propagate through spatially contiguous regions of physical space at finite speeds, have been found to be extremely fruitful, and the need for “action at a distance” has in general been disparaged, as for example by Einstein’s demonstration that it is not needed in order to explain gravitation, in contradistinction to Newton’s the­ ory. It must be admitted though that this subject is not yet closed to controversy, especially in view of certain holistic quantum mechan­ ical effects.7

146

The question arises then as to whether this principle of the spatial contiguity of causes and effects is also applicable outside the realm of strictly physical causal chains; specifically whether it is applica­ ble to the causal connection between neural events in the brain and phenomenal events, such as color changes in visual space, assum­ ing for the moment that these phenomenal events are not numeri­ cally identifiable with physical events, as held by dual aspect theor­ ies. Until some reason is shown as to why the principle of the spatial contiguity of causes and effects is not applicable to causal connec­ tions of this type, it would seem prima facie to be a reasonable working hypothesis to assume that it is in fact applicable, and then see whether or not such a hypothesis can help to elucidate the problem of mind body causal connections by critically examining the various logical implications of it. If such an analysis does not turn out to be fruitful, one would then have evidence that such a spatial constraint does not in fact apply to mind body causal con­ nections, and one might even feel compelled then, along with Malebranche and Leibniz, to deny the very existence of these causal connections, perhaps holding, like them, that the two merely run “parallel” with each other. Two logical implications of the foregoing analysis of the spatial constraints on causation can be noted at once. Both of these involve the issue of whether the mind (by “mind” I am just referring here to consciousness, as epitomized by the existence of phenomenal space, and thus am not for, example, concerned with any Freudian consid­ erations of the unconscious) is spatially extended or not. First, it would follow that if the mind is not spatially extended (assuming, in contrast to Descartes, that it still possesses a definite location in physical space), then it could at most only be causally connected with one physical point of the brain. This is because causal connec­ tions must be spatially contiguous according to the foregoing anal­ ysis, and since obviously a spatially unextended mind could not be spatially coextensive with more than one physical point. Also, it would follow that if the mind is spatially extended, and if this spatial extension is spatially coextensive (in the sense of occupying the same spatial dimensions) with physical space, then a region of the brain would have to possess at least a topologic isomorphism with the mind. By a “topologic isomorphism,” I refer to the fact that close points in one space possess corresponding close points in the topologically isomorphic space, although the metric relationships

147

among these points may still differ. Such an isomorphism would be required here in order that causally connected portions of the mind and the brain could be spatially contiguous with each other. Inas­ much as both of these principles involve the issue of whether or not the mind is in fact spatially extended, it would seem to be wise to investigate that issue now in some detail. The claim that the mind is not spatially extended can be traced back at least to Aristotle, who argued for it as follows in De Anima.

Mind is either without parts or is continuous in some other way than that which characterizes a spatial magnitude. How, indeed, if it were a spatial magnitude, could mind possibly think? Will it think with any one indifferently of its parts? In this case, the “part” must be understood either in the sense of a spatial magnitude or in the sense of a point (if a point can be called a spatial magnitude). If we accept the latter alternative, the points being infinite in number, obviously the mind can never exhaustively traverse them; if the former, the mind must think the same thing over and over again, indeed an infinite number of times (whereas it is manifestly possible to think a thing only once). (De Anima, 407A) Aristotle here argues that the mind would be separate from its parts and have to “inspect” each of these parts individually if the mind was spatially extended. However, the question can at least be raised as to why the mind need be separate from its parts here. To study this question, it is instructive to examine the arguments of a number of subsequent philosophers who have made a series of related argu­ ments on this issue of the spatiality of the mind, particularly on the questions of whether the mind’s being spatial entails that it have parts, and on whether such parts would have to be distinct and or separate from each other. Hume, for example, tried to argue that the mind’s separability into parts follows from the distinctness of these parts, and, whereas he concluded from this that there is no basic unity to the mind (Hume’s bundle theory of the mind), other philo­ sophers, notably Descartes, used this same purported connection to argue that the mind is not spatial. Hume made this connection between the mind’s distinctness into parts and the separability of these parts as follows:

As to the first question; we may observe, that what we call a mind, is nothing but a heap or collection of different perceptions,

148

united together by certain relations, and supposed, though fal­ sely, to be endowed with a perfect simplicity and identity. Now as every perception is distinguishable from another, and may be considered as separately existent; it evidently follows, that there is no absurdity in separating any particular perception from the mind; that is, in breaking off all its relations, with that con­ nected mass of perceptions, which constitute a thinking being. (Treatise of Human Understanding, p. 207)

Thus, Hume is arguing here from the connection between “distinct­ ness” and “separability” to the conclusion that there is no deep unity to the percepts in our minds; their constituting instead merely an aggregate or bundle. However, Descartes in the following pas­ sage from his Sixth Meditation makes use of the same alleged con­ nection to argue that the mind is not spatially extended. In order to begin this examination, then, I here say in the first place, that there is a great difference between mind and body, inasmuch as body is by nature always divisible, and the mind is entirely indivisible, Eor, as a matter of fact, when I consider the mind, that is to say, myself inasmuch as I am only a thinking thing, I cannot distinguish in myself any parts, but apprehend myself to be clearly one and entire; and although the whole mind seems to be united to the whole body, yet, when a foot, an arm, or some other part, is separated from my body, I am aware that nothing has been taken away from my mind. And the faculties of willing, feeling, conceiving, etc. cannot properly speaking be said to be its parts, for it is one and the same mind which employs itself in willing, and in feeling, and understanding. But it is quite otherwise with corporeal or extended things, for there is not one of these imaginable by me which my mind cannot easily divide into parts, and which, consequently, I do not recog­ nize as being divisible. (Philosophical Works. Vol. 1. p. 196)

I wish to show now that both Hume and Descartes are mistaken in their claim that it follows from the fact that two or more aspects of the mind can be distinguished, that they can also be separated from each other. One set of counterexamples that can be given to this alleged connection is connected with an argument which Berkeley made in his critique of Locke’s theory of abstract ideas—namely that even though some concepts, such as size and shape, or per­ ceived color and perceived size or shape, are distinct concepts, it nevertheless is the case that they are inseparable; i. e., we cannot

149

conceive of one without also conceiving of the other. This shows that being distinct does not at least logically entail being separable, and I wish to show now that there are even cases of physical spatial distinctness where the distinct parts are not separable. Consider the case of the north and south magnetic poles. Assuming that mag­ netic monopoles do not exist, it would seem that the two must always be paired together even though they are distinct. Thus, it would seem that it is at least possible that something be spatially extended and have distinct parts in the different spatial locations, but not have those parts be separable from each other. As I noted in Chapter Two, Kant claimed that there was a basic unity to the mind which he called the “transcendental unity of apperception.” Kant8 argued for this unity by first pointing out that since we are consciously aware of all the percepts in our own minds, but not of those in other minds, and then arguing that there must be a way to differentiate between the two cases. However, pointing out this unity merely names the solution, and does not explain how the unity can in fact take place. My discussion of the phenomenal eye regress is relevant here though, since I argued there that the very existence of a continuous phenomenal space is sufficient to consti­ tute perception—the existence of visual space constituting visual perception—in the sense that nothing more is required for the pur­ pose of viewing or scanning events in the space. Thus, the claim would be that we can be aware of the whole of a phenomenal space, including its qualitatively different parts, at once, due to the very phenomenal character of the space. Also, even though we can con­ ceptually refer to the various parts of the space, as I have previously analyzed, there is no reason to think that such an act would affect the spatial unity of the experience. I would like to turn now to a discussion of an argument which Pierre Gassendi raised in objec­ tion to Descartes, that inasmuch as the mind is capable of appre­ hending spatially extended objects, it too must somehow be extend­ ed. Gassendi argued as follows: For, if such a semblance proceeds from the body, it is certainly corporeal and has parts outside of other parts, and consequently is corporeal. Or alternatively, whether or not its impression is due to some other source, since necessarily it always represents an extended body, it must still have parts and, consequently, be extended. Otherwise, if it has no parts how will it represent parts? If it has no extension how will it represent extension? If

150 devoid of figure, how represent an object possessing figure? If it has no position, how can it represent a thing which has upper and lower, right and left, and intermediate parts? If without variation, how represent the various colors, etc.? Therefore an idea appears not to lack extension utterly. But unless it is devoid ofextensionhowcanyou.if unextended, be its subject? How will you unite it to you? How lay hold of it? How will you be able to feel it gradually fade and finally vanish away? (The Philosophi­ cal Works of Descartes, Vol. 2, p. 196, 197) Descartes9 replied to Gassendi by claiming that the mind could “apply itself’ to spatially extended things without thereby itself becoming spatially extended. LeibnizlO made a similar claim here, holding that even though minds (monads) do not take up space, they are still at least capable of spatial perception, and this is also related to Aristotle’s talk about the mind traversing its parts. In reply to all three philosophers I would first point out that the possession of percepts is a conscious property, and note that I have analyzed the percepts as possessing a spatial structure. I have also shown that they are not just spatial in the abstract sense of being mathemati­ cally characterizable in terms of arrays of numbers, but instead literally do take up space, although it may be a legitimate issue as to whether or not this perceptual space is coextensive (in the sense of occupying the same dimensions) with physical space. I thus con­ clude that it is a reasonable hypothesis to hold that the mind is in fact spatially extended. This finishes my discussion of constraints on mind body causal connections, and thus I shall now turn to a discussion of how one particular physiological sensory system, the visual system, is set up.

151

5.2 The Neurophysiology of Visual Perception

In this section I shall summarize certain aspects of the neurophysi­ ology of visual perception, to the extent that this subjectis currently understood. It needs to be emphasized though that much of the relevant physiology is still only very poorly understood, particu­ larly concerning neural processes beyond the visual cortex. In Chapter Two I gave a brief summary of physiological optics, and discussed how the rods and cones of the retina serve as light detectors upon which the visual image is displayed. In my section on visual orientation I also noted that the eyes are in almost continuous motion, and that thus the image displayed upon the rods and cones of the retina is almost continuously changing due to these eye movements. I will now briefly expand on my earlier treatment of eye movements, and will then move on to a discussion of the neurophy­ siology of the retina. There are several different types of eye movements, the most common being saccades, where, after a short period of either facing in the same direction or slowly drifting (that is slowly changing direction), the two eyes, usually involuntarily, make a sudden shift in direction of a few degrees or more. There are also voluntary eye movements where the eyes make a comparatively large change in direction so that an object of interest can be brought so that its optical projection falls directly onto the fovea so that it can be see more clearly. It is also worth noting that when either the direction < the eyes is held fixed, or if a homogeneous field of light is projecte onto the retina, after a few seconds the photoreceptors of the retina will no longer be receptive to the display, resulting in the pheno­ menal experience of the so-called “empty field.” The role which eye movements serve in visual perception is a controversial topic, with some psychologists, notably J. J. Gibson, claiming that they are of fundamental importance, while others tend to downplay them, and instead emphasize the fact that the retinal image is an image. Gibsonll argued that visual perception works by means of a relatively small portion of the retina (chiefly the fovea) sampling various sections of the array of “ambient light” (light reflected from objects as opposed to “radiant light” which radiates in all directions from a common source) which enters the eye, and discovering invar­ iant structures in it. Due to the just discussed eye movements, Gib­ son held that visual perception can still retain a comparatively wide

152

field of view, while only making intrinsic use of a comparatively small region of the retina. Regardless of the merits of Gibson’s theory here, the problem does arise as to how the visual perception system takes eye movements into account in its reconstruction of physical surfaces being seen, and it needs to be emphasized that we are usually completely unaware of saccades taking place. I shall have more to say on this problem later, but will now turn to my discussion of the neurophysiology of the retina. In Chapter Two I noted that the rods of the retina are homogene­ ously sensitive to light intensity, while there are different types of cones, which, while being somewhat less sensitive to light intensity than the rods, vary in their sensitivities to different wavelengths of light. It is now generally agreed that there are three different types of cones (“blue cones” are much more rare than the others, and fora while there was a controversy as to their very existence), each being maximally sensitive to a different wavelength of light. Thus, infor­ mation from three different types of color receptors is available in order for the colors of objects being “seen” to be reconstructed at a “higher stage” of the visual perception process. It was also noted in Chapter Two that the cones are most densely concentrated in the central fovea of the retina, the center of which is devoid of rods, and that the concentration of cones steadily diminishes towards peri­ pheral regions of the retina, which are completely dominated by rods. There are approximately 7 million cones and 100 million rods in the retina. Somewhat oddly, both the rods and the cones face the back of the retina, and the amount of light which can reach them is considera­ bly reduced by this fact, together with the fact that there is a large array of blood vessels and neurons immediately in front of the retina. Two important types of these neurons are the bipolar cells and the ganglion cells. The rods and cones are connected to the dendrites of the bipolar cells, and these cells in turn are connected to the ganglion cells. While a single ganglion cell is usually connected to a large number of rods, in the case of the fovea at least there are as many ganglion cells as cones, although there is still some overlap among cones in the receptive fields of these cells. In any event though, very little integration occurs among different cones at the retinal level. Ganglion cells possess circular receptive fields, and are most sensitive to small spots of light and regions of light contrast (as occurs in “edges” in an image). There are three different types of

153

ganglion cells; W cells whose feature detection abilities are not well known, X cells which are sensitive to relatively sustained patterns of contrast, and Y cells which are sensitive to transient patterns. None of these types responds well to relatively uniform illumina­ tion. The optic nerve consists of the axons from the ganglion cells, and leaves the retina at the blind spot (the area near the fovea where no rods or cones are present). The optic nerves from the two eyes meet at the optic chiasm, from which the axons of ganglion cells correlated with the left hand sides of both retinas are sent to the left hemis­ phere of the brain, and those correlated with the right hand sides of both retinas are sent to the right hemisphere of the brain. Thus, at the optic chiasm, information from the left and right sides of the optic arrays impinging on the retinas of the two eyes, is split, since it is subsequently projected onto spatially distinct, although parallel, structures of the respective two hemispheres of the brain. While there are certain interhemispheric connections, notably by way of the corpus callosum, this early split in the visual perception process does raise the problem as to how a single phenomenal visual space can be constituted from information projected to the two sides, and I shall return to this problem later.12 After leaving the optic chiasm, the two reorganized optic nerves lead to the respective lateral geniculate bodies of the thalamus, which serve as “relay stations” from which axons branch out to the visual cortex. There is continuous electrical activity in the lateral geniculate bodies, which is mediated by signals from the optic nerves, and thus it is clear that a certain amount of recoding takes place in these bodies. However, it is noteworthy that the nerve inputs from the respective eyes are kept separate here, being pro­ jected onto different layers of the bodies, and thus it is evident that no binocular integration takes place at this level. There is also evidence that signals from the X and Y ganglion cells, along with signals pertaining to color information, are segregated by different layers of the bodies.13 It should also be noted that some of the axons comprising the optic nerves go to the superior colliculus rather than the lateral geniculate bodies, and that a few go to a body, the pretectal nucleus, which regulates the size of the pupil. The superior colliculus, a structure in the brain stem, is interesting inasmuch as it also receives input from the visual cortex, along with input from the other sensory systems,

154

Left Hemisphere Lateral Geniculate Body

Optic Chiasm R L'

^L R

Visual Cortex Corpus x Callosum

R L~

L

Right Hemisphere Figure 5-1

L T.

Lateral Geniculate Body

Diagram of the visual pathways to the visual cortex

notably the auditory and somatic ones. Its function seems to be concerned with orientation, motion detection, and the control of eye movements. I shall now turn to my discussion of the visual cortex. The visual cortex is comprised of Brodmann’s areas 17, 18, and 19. Area 17, which is by far the largest of these areas, is sometimes also called the “primary visual cortex,” or the “striate cortex” (due to a stripe which is clearly visible in a cross section of it). All of these areas are located at the posterior end of the cerebral cortex, which is the surface structure of the cerebrum where most of the “higher” infor­ mation processing in the brain takes place. The cerebral cortex, from a macroscopic viewpoint, approximates being a two-dimen­ sional surface in the sense that two of its dimensions are much greater than the third; it being approximately 500 square centime­ ters in area, and varying in thickness from about 2 to 5 millimeters (it is especially thin, about 2 millimeters, in the region of the visual cortex). It possesses a large number of folds in order to allow for such a large surface area to fit in within the confines of the skull. The

155

primary visual cortex, in turn, is approximately 15 square centime­ ters in area, and is comprised of six distinct layers. A large amount has been learned about the responses of individ­ ual neurons in the visual cortex to particular optical stimuli by means of techniques involving the use of microelectrodes, which measure the electrical potentials of neurons for these stimuli For example, David Hubei and Torsten Wiesel of Harvard Medical School received the 1981 Nobel Prize in Medicine for their important work in this area. Inasmuch as all of these experiments have been conducted on animals—chiefly the cat and the monkey—due to th obvious ethical implications of experiments on humans, there might seem be some questionHowever, regarding the validity ofoverall generalize these to results to humans. inasmuch as the strug

tures of these visual systems seem to be comparable, although mo ° highly developed, in man, it would seem to be a plausible hypothesis to hold that the microstructures are also closely analogous In a event, this would seem to be the only viable working hypothesis with which to proceed, in view of the just noted ethical implications of experiments on man. Using the microelectrode technique, it has been discovered that points of the retina are mapped onto the primary visual cortex and subsequently onto the two neighboring areas, 18 and 19, in a’two-

dimensional fashion. This projection is two-dimensional not only in the sense that, as I just noted, two of the dimensions of the surface being projected onto are much greater than the third, but also in the sense that the neurons in a given section of the cortex will only respond electrically to stimuli impinging on a relatively small cor­ responding section of the retina, with close retinal areas being corre­ lated with close cortical areas. Thus, there is clear evidence for at least a topologic isomorphism (whereby, as I previously noted, close points are mapped onto close points, but where metric relationships are at least not necessarily preserved) between the retina and regions of the visual cortex, due to the foregoing correlation of close retinal areas with close cortical areas. However, it is noteworthy that this isomorphism is not also metrical, since the area of cortical regions corresponding to foveal regions of the retina is dispropor­ tionately large when compared to cortical regions corresponding to peripheral regions of the retina. There is a fair amount of correspon­ dence between the resolvability of a given region of visual space and the corresponding cortical area though, and it also appears that

156 90 r-......

80

70 60

50>... 40 30 20, 10.

10 20 30

40 50> 701 80 L

901

Figure 5-2 A, representing the right half of the retinal image using polar coordinates centered in the fovea, is projected onto the visual cortex as B. Similar markings refer to corresponding areas. (Due to Holmes, 1945)

there may be a logorithmic magnification effect taking place here.14 Lorrin Riggs takes note of this magnification effect as follows: One significant aspect of cortical projection areas is the apparent magnification effect. Talbot and Marshall found,’ in the cat, that the cortical projection area was laid out to a scale of one millimeter per 5° visual angle in peripheral vision and one millimeter per 1° in central vision. In the monkey, corresponding figures per millimeter of cortex were 18 minutes visual angle for the periphery, 2 minutes for the fovea. The important conclusion from this is that the monkey, whose visual system is closely similar to our own, is provided with a large-scale map of the visual field. In fact, the ratio of cortical to retinal projection areas in the primate fovea was estimated by Talbot and Marshall to be 10,000 to 1. (Riggs, 1965, p. 115)

157 As in other cortical regions, the neurons of the visual cortex are arranged in columns, in this case with each column being correlated with a particular region of the retina, and the columns alternating as to which eye dominates them.15 Ocular dominance refers to the fact that the.neurons in a given column can either only be driven by stimuli impinging on one eye, or at least will fire at a higher rate for that eye, although still being responsive to binocular stimulation. A group of ocular dominance columns for the different eyes, but all correlated with the same retinal region, has been called a “hyperco­ lumn” by Hubei and Wiesel, 15 and thus hypercolumnscan be taken as the “points” of the visual cortex which bear a topologic isomor­ phism with the “points” (i. e., photoreceptors) of the retina. The neurons in the ocular dominance columns are only excited by highly specific visual stimuli, such as edges of both a particular size and angular orientation. Thus, these neurons are much more res­ trictive in the patterns which they are responsive to than are the ganglion cells of the retina. These neurons can also be divided into three classes—simple, complex, and hypercomplex—depending upon the angular size of the stimuli which they are responsive to, and whether these stimuli are moving or not. Simple cells are most sensitive to optimally oriented edges in comparatively narrowly defined locations, whereas complex cells are less particular about the exact locations of their stimuli, and prefer a given direction of movement for the edges. Hypercomplex cells in turn are sensitive to either edges that have stopped in a particular direction, or corners moving in a particular direction. It is possible that simple cells are driven by signals from X ganglion cells and that complex cells an driven by signals from Y ganglion cells, since both Y cells an< complex cells are responsive to motion, while both Xcells and simple cells respond best to stationary patterns. Thus, it is clear that at least one of the primary functions of the primary visual cortex concerns pattern recognition, and Hubei and Wiesel have expressed the opinion that it represents a still early phase in the visual percep­ tion process. 1? It also seems to be the case that the feature detection performed in the primary visual cortex is used in “higher” types of image analy­ sis, and in fact a branch of Cognitive Science has developed for studying the type of image analysis performed by the visual cortex, this being the computational approach to visual perception. Much ot this work has been centered around M.I.T., where for example

158

1

R

2

L

3

R

4

L

R

L

5

R

L

6

R

L

R-

L

Figure 5-3 Shimon Ullmanlb has worked on models of how visual motion, including the rotation of objects, may be analyzed, and David Marrl9 has worked on how the visual cortex may analyze cues for depth and surface orientation made use of in his 2 ‘Z>-D sketch, which I will discuss in the next section. Much work has also been done on the analysis of stereopsis, and I shall now turn to a brief discussion of how the visual cortex may handle that problem. Bela Julesz20 has argued that pattern recognition must be involved in stereoscopic depth perception, inasmuch as correspond­ ing retinal points must be identitified by some sort of matching process, in order to discover the degree of retinal disparity involved. Much work has been done on possible matching models in this regard2l and the general idea behind one possible such model is shown in Figure 5-3, where patterns determined in the various ocu­ lar dominance columns of the visual cortex are later matched in order to identify the amount of disparity involved. It should also be noted that neurons have been discovered in the visual cortex which are only sensitive to specific amounts of retinal disparity,22 and thus it is clear that the visual cortex itself is involved with the foregoing matching process for stereoscopic depth perception. Hu­ bei and Wiesel took note of these disparity sensitive neurons as follows:

As an electrode traverses the cortex, sequences of cells that are all ordinary, or all of the binocular depth type are recorded; neighboring binocular depth cells often have the same horizon­ tal disparity, though varying in orientation. This suggests an organization in which cells representing a given stereoscopic

159

I l-H-l I Receptive Fields of Neurons

Figure 5-4

The Principle of Lateral Inhibition

depth relative to the surface of fixation are grouped together, and segregated from cells that are not particularly concerned with depth. These groupings may have the form of columns that extend from surface to white matter. (Hubei and Wiesel, 1970, p. 41)

Thus, Hubei and Wiesel suggest that these disparity sensitive neurons may be grouped by columns, with different columns being sensitive to different amounts of horizontal disparity. Research in this area has continued, notably with the work of G. F. Poggio,23 and in at least the case of sheep (whose eyes are relatively wide apart), positive evidence has been discovered for such disparity segregation by different columns.24 One other feature of neuronal activity in the visual cortex which should be discussed here is the phenomenon of lateral inhibition, which is illustrated in Figure 5-4. In lateral inhibition, which also occurs in other structures of the brain, a neuron firing most strongly for a given pattern and retinal location will tend to inhibit surround­ ing neurons from firing. Thus, more spatial acuity is projected onto the visual cortex than one might think by just considering the respective sizes of the various neurons’ respective fields themselves. This point bears importance to an argument presented in my next section, where I examine the possibility that there is a causal link between events occurring in the visual cortex and phenomenal ones in visual space. Comparatively little is known about what occurs in the visual perception process past the visual cortex since fewer detailed microelectrode studies have been conducted on regions subse-

160

Visual Cortex 17, 18, 19

Precentral Agranular Field

0-

Superior Temporal Sulcus

21

Figure 5-5

The Cortical Progression of Visual Perception

quently projected onto. Also, much of what is known has been discovered by means of much “rougher” techniques than the microelectrode work, such as by studying the results of brain lesions, although recently this picture has been changing. Aside from projections from the visual cortex back to the lateral geniculate bodies and into the brain stem, notably to the superior colliculus, it is known that a number of frontal regions of the cerebral cortex are also projected onto. Jones and Powell25 have summarized these findings, noting that projections go from the visual cortex to Brodmann’s area 20 and area 8 A, the prefrontal eye field, whose neurons possess very wide retinal fields. These projections are followed by reciprocal projections to the precentral agranular field and Brodmann’s areas 21 and 46. Area 21 is projected onto the superior temporal sulcus, in the depths of which it is joined by projections from the somatic and auditory perception systems, and projections from all these areas are subsequently sent into the brain stem. The progression of these projections is traced out in Figure 5-5 (due to Jones and Powell) where each new projection site is shown in black,

161

and other connections are shown by the lightly shaded areas. It is noteworthy that there is a convergence of sensory systems (visual, somatic, and auditory) as these systems progress into asso­ ciation areas of the cerebral cortex, such as the superior temporal sulcus. It should also be noted though that neurons in these associa­ tion areas tend to have quite wide retinal receptive fields, these being on the order of 30° - 60° for the superior temporal sulcus. There is also evidence that many of these neurons are only sensitive to highly specific types of stimuli, some apparently only firing for stimuli shaped like faces or hands,26 although there is a controversy as to whether it is these features which are really being selected for. I shall argue in my next section that these last considerations pose problems for any theory which postulates one of these association areas as constituting a site for a causal connection with pheno­ menal space due to the large amount of spatial acuity present in at least the visual portion of that space. This finishes my summary of the neurophysiology of visual per­ ception, and I shall now investigate the question of which of these visual processing areas in the brain is immediately causally asso­ ciated with the production of phenomenal events in visual space.

162 5.3 Potential Neural Sites for Mind Body Causal Connec­ tions

In this section I will investigate the question as to which region, or series of regions, of the brain possess physical events (presumably electrical events) which are the immediate causal precedents to phenomenal events in phenomenal space, in particular visual ones. There has been a fair amount of controversy over this issue, since some neurologists, notably Wilder Penfield,2? have argued that consciousness is causally associated with a comparatively “late” stage in neural processing, Penfield in fact holding that it occurs in the brain stem after information has been sent there from cortical areas. Hubei and Wiesel, as I noted in my last section, have argued similarly that neural activity in the visual cortex represents a still early phase in the visual perception process, with conscious expe­ rience being associated at least with a much later phase. In spite of these positions to the contrary, I will argue here that conscious visual perception is causally associated with a comparatively early phase in neural processing, in fact occurring in one of the visual projection areas (probably area 17) of the visual cortex. I will be defending a theory of geometric isomorphism here between neural events in cortical areas and phenomenal events in visual space, and a key point will be that only in the visual cortex is there a sufficient degree of spatial acuity in neural electrical activity for such an isomorphism to exist. To begin my investigation, one can take note of the second princi­ ple concerning mind body causal connections which I discussed earlier; that if phenomenal space is spatially coextensive with phys­ ical space, and if the principle of the spatial continuity of cause and effect applies to mind body causal connections, then a region of the brain would have to possess at least a topologic isomorphism with phenomenal space, with causally connected parts of the two being spatially contiguous with each other. Thus, the question arises as to whether or not any neural structures possess such a topologic isom­ orphism, and if more than one does, how to determine which of these is causally immediately involved with the determination of events in phenomenal space. As I noted in my last section, there are a number of regions of the brain which possess topologic isomorphisms with the retinal image, including the lateral geniculate bodies, the superior colliculus, the

163

projection centers of the visual cortex, and various visual projec­ tions in association areas of the cerebral cortex. Some of these can be immediately eliminated as being sites of mind body causal connec­ tions though. The lateral geniculate bodies can be eliminated, since there is no binocular interaction between the eyes there, whereas this would be necessary for binocular visual depth perception. Also, the superior colliculus can be eliminated (although it does possess convergent projections from audition and touch onto a visual pro­ jection area),28 since it seems to be the system responsible for such phenomena as blindsight, where we are not conscious of a visual stimulus but can still locate it either by eye movements or by point­ ing. The argument behind this claim involves the point that since one of the primary functions of the colliculus involves orientation, and since blindsight also just involves orientation, without the abil­ ity to identify the stimulus, the colliculus must be the structure mediating the phenomenon.29 This leaves the visual projection cen­ ters in the visual cortex and the remainder of the cerebral cortex as possible sites, and I shall now turn to a discussion of what evidence there is that any of these possess a sufficiently close topologic isom­ orphism with events in visual space. A theory of spatial isomorphism between physical events in the visual cortex and phenomenal events in visual space was first deve­ loped by certain members of the Gestaltist school of psychology, most notably Wolfgang Kohler.30 Kohler claimed that electrical events in the visual cortex are both spatially isomorphic with physi cal objects being perceived, and also with phenomenal events in visual space. He was unclear as to exactly what type of spatial isomorphism he was referring to here though, but it is possible that it was even a metric isomorphism, in view of the Gestaltists' claims of absolute size and shape constancy in visual perception. Since I disputed the claim that these constancies are absolute in Chapter Three, it would seem that the alleged isomorphism between the physical objects being perceived and events in visual space could at best be only topologic, but the possibility would remain that there is a metric isomorphism between electrical events in the visual cortex and events in visual space. Kohler claimed that this latter isomor­ phism was with macroscopic direct currents in the visual cortex, but the specific details of such a theory would seem to have been dis­ proved by Karl Pribram,31 who was able to distort these currents with no noticeable effect occurring in visual perception.

164 A theory of spatial isomorphism between events in visual space and electrical events in the visual cortex could be saved from Pri­ bram’s refutation though by claiming that the isomorphism is not with macroscopic electrical activity in the visual cortex, such as the direct currents suggested by Kohler, but rather with the separate electrical potentials of individual neurons there. In my section on the neurophysiology of visual perception, I noted that the retinal image is projected onto the primary visual cortex (Brodmann’s area 17), and subsequently onto two neighboring regions (areas 18 and 19), in a manner which is topologically, but not metrically (due to the exaggeration in size of areas corresponding to foveal regions), iso­ morphic with the retinal image. I also noted there that the retinal fields of some of the simple cells of the primary visual cortex corres­ ponding to foveal regions are comparable in size (sometimes sub­ tending as little as 2 minutes of visual arc) to the maximum spatial acuity present in visual space. If the principle of lateral inhibition is also taken into account here, which I previously argued can account for an even greater amount of spatial acuity being present, it would seem that there is a sufficient amount of spatial acuity present in the electrical activity in neurons in the visual cortex for it to be isomor­ phic with events in visual space. While still on the subject of spatial acuity, it should be noted that all subsequent projections of visual information onto regions of the cerebral cortex past the visual cortex, including those in association areas, as far as is currently known involve much larger retinal fields for their neurons. In fact, these fields are sometimes as large as a quadrant of the whole visual field. Thus, there would be difficulties in explaining how the electrical activity in neurons in any of these regions could account for the spatial acuity present in visual space, even taking the principle of lateral inhibition into account, while this spatial acuity would seem to be accountable for in terms of the electrical activity of neurons in the primary visual cortex, as I have just shown. Of course, I have also pointed out that the neurons in the visual cortex are engaged in feature detection, being most sensitive to edges at given angles, or in different directions of motion, and it would thus seem that there is no precise isomorphism between vis­ ual space events and the electrical activity of these neurons. I might note though that neurons located in projection areas past the visual cortex are even more specific than those located in the visual cortex

165 about stimuli features being selected for, some, as I noted in my previous section, apparently only firing for stimuli shaped like faces or hands. Another problem for a theory of isomorphism with the visual cortex is that the visual cortex projections are retino-centric; that is, where cortical columns are correlated with particular retinal points, whereas visual space is so oriented that objects constituted in it at least normally (i. e., in the absence of vertigo) remain station­ ary in spite of head and eye movements. It is interesting that a number of the problems just discussed for a theory postulating a geometric isomorphism between phenomenal events in visual space and neural electrical events in the visual cortex could be avoided if neurons in one of the visual projection centers there were performing something akin to what David Marr32 has called the “2 'A D-sketch.” Before I discuss the nature of this sketch in some detail, it should be pointed out that the evidence for the existence of the processes referred to in it is not physiological, but that instead the sketch arose from artificial intelligence work in machine vision, when it was discovered that prior to the identifica­ tion of objects being “seen,” it was necessary to determine their three-dimensional shapes, and that a crucial stage in this determi­ nation involved the 2 ‘A-D sketch. It can be noted though that neural evidence has been found for other facets of Marr’s analysis here, including that ganglion X cells in the retina can be used for the detection of “zero crossings” (locations in an image where the light intensity passes from positive to negative with respect to the aver­ age intensity) which are key factors in what Marr calls the “primal sketch,” a precursor to the 2 ’A-D sketch, and that certain neurons in the visual cortex are sensitive to particular retinal disparities, this identification being necessary for binocular depth perception. Also, there is some recent evidence from visual agnosias that a threedimensional analysis of object shape (which for Marr’s analysis is the next step past the 2 ’A D sketch) is necessary before objects are verbally identified, since there are case studies33 of subjects who can identify the two-dimensional shapes of objects being seen, but who are not able to semantically recognize them, even though their other semantic capabilities are intact. This shows that an interme­ diary pre-semantic stage of visual processing is missing here. In the 2 *A-D sketch, depth, surface orientation, and surface dis­ continuity information concerning the objects being “seen” is dis­ played on a two-dimensional continuum within a viewer-centered

166

coordinate frame. It should be emphasized that from a topologic point of view the continuum being displayed on here is only twodimensional, even though, from an information theoretic stand­ point, each pointon the continuum also contains depth information (the '/i-D). It should be noted that specific a priori knowledge con­ cerning the shapes of objects being seen is not presupposed in the construction of the sketch, since instead Marr shows how the details of the sketch follow from just a few presuppositions of constraints on properties of objects being viewed, notably that they are rigid and possess continuous surfaces. It is also noteworthy that the informa­ tion from the visual perception system is usually much more specific concerning relative depths (and hence just concerning surface orientation) than it is for absolute depths, since such cues as visual motion only give information about relative depths, and even such cues as retinal disparity are much better at telling about relative depths than they are about absolute depths. It should be obvious then that there is a close geometric isomor­ phism between my variable curvature theory of the metric structure of visual space and Marr’s 2 ‘/2-D sketch just outlined, since both claim that visual information is displayed in a topologically twodimensional format and that depth information is also present here, either in terms of local changes in curvature due to my depth func­ tion, or else as the depth and surface orientation information pres­ ent in the ‘/2-D part of the 2 ’/2-D sketch. A possible objection could be raised here though in that the visual projection onto the visual cortex is oculo-centric (i. e., with cortical points being correlated with retinal points), while, as I have noted in my section on visual orien­ tation, visual space is oriented so that objects constituted in it remain stationary in spite of head and eye movements. One way around the foregoing objection would be to claim that the whole of visual space itself moves with respect to the visual cortex in order to compensate for head and eye movements. The vestibular system of the brain takes account of corporeal movements by means of using the various orientation cues arising from the centrifugal force of a fluid contained in the semicircular canals of the inner ear, and breakdowns in this system cause the whirling sensations of vertigo which I analyzed in my section on visual orientation. How­ ever, little is known concerning how these vestibular cues are used by the brain in order to keep visual space oriented so as to remain stationary with respect to the physical world. Thus, it would be too

167

speculative at this point to postulate any particular mechanism via which visual space is kept in motion with respect to the visual cortex so as to compensate for the changing ocular projections displayed upon it. This last suggestion, that visual space moves with respect to the visual cortex, may also be relevant for answering another possible objection to the claim that events in visual space are causally determined by electrical activity in the visual cortex. This objection arises from the fact, which I noted in my section on the geometry of phenomenal space, that information from the different sensory sys­ tems is displayed upon one common phenomenal space, with infor­ mation from the different sensory modes often being displayed on the same area of the space. For example, I noted that when one is either viewing the source of a sound, or looking at one’s hand while pinching it, sensations from different sensory modes are sensed at the same location. This raises the problem as to how spatial infor­ mation from the different sensory systems is integrated together by the nervous system. One possible move to make here would be to claim that this spatial integration takes place by means of sensory inform ation from the different sensory systems being projected onto one common neural structure. This would not solve the problem for a mind body causal connection with the primary visual cortex though, since it is known that only visual information is projected there. However, another possible solution to the problem of sensory spatial integration involves postulating that information from the different sensory systems is projected onto spatially distinct neural structures—the visual cortex for visual information, the somatic cortex (which possesses a fine-grained topologic isomorphism with the surface of the body)34 for tactile information, and possibly the auditory cortex (which, however, does not seem to possess a topo­ logic isomorphism with the directions of sounds) for auditory infor­ mation. The claim then would be that events in phenomenal space are constituted by means of the whole spherical phenomenal space revolving with respect to these different neural structures, picking up relevant sense information in the appropriate locations as it passes by each structure. In my next section, I shall discuss details of the topology for how a phenomenal space could be located so as to be spatially contiguous to the foregoing neural structures, and also show how there could then be causal connections between correlated

168 events in the two. I will now close this section by presenting two further arguments for holding that visual experience is causally associated with neural events in the visual cortex; one from the results of brain lesions, and one from evidence from event related potentials (ERPs) involving attention. My argument from the results of brain lesions is as follows. When humans lose the complete visual cortex, as from surgery or gunshot wounds, they report being blind, although even here they are some­ times able to respond appropriately to visual stimuli in the pheno­ menon known as “blind sight,” where as I previously noted the controlling mechanism is completely unconscious. In the case of partial lesions of the visual cortex in humans, “scotomata” result; these being blind regions, in the sense that the person having them will not at least be consciously aware of objects projected onto corresponding sections of the retina, as with the blind spot. Pheno­ menally, there are two different results which may occur here— either the intervening phenomenal space will be interpolated to be the same as its surroundings, or else the phenomenal space will “collapse” around the scotoma, so that regions which are not physi­ cally adjacent to each other will be seen as being adjacent. These last facts do not necessarily prove that visual experience is causally associated with neural events in the visual cortex, inasmuch as it would be possible that these lesions merely interrupt the physical causal chains of the visual perception process (similar deficits, for example, occur when parts of the optic nerves are severed), with the actual causal determination of events in visual space being asso­ ciated with a still later neural stage. However, since there are paral­ lel visual projections, which bypass the visual cortex, onto many of the areas which are subsequently projected onto, it would seem that the results from lesions at least constitute evidence for the causal connection with visual experience there.35 My second argument here involves evidence from event related potentials, which are measured by electrodes placed on the scalp. It has been found that the magnitude of electrical potentials in the visual cortex is increased during the attending to of events in cor­ responding regions of visual space. For example, Harter, Aine, and Schroeder36 have shown that when events in one half of the visual field are attended to, there is a concomitant increase in electrical potentials in the corresponding hemisphere of visual cortex, but not in the other hemisphere. Since these heightened electrical potentials

169 begin when the visual stimuli are first attended to, and since atten­ tion here corresponds to the conscious visual apprehension of the stimuli, it would seem that the two must be causally correlated together. Otherwise, time would be required for the relevant visual signals to travel to the other regions of the brain where further visual information processing takes place. Thus, I conclude that there is quite a bit of evidence from several disparate source that phenomenal visual experience is causally associated with neural electrical activity in the visual cortex. I shall now turn to an investigation of the relative merits of dualistic and dual aspect solutions to the mind body problem, and, in the course of that investigation, I will discuss details of how a two-dimensional phenomenal space could be “embedded” in a structure of the brain, so that events in it could be causally determined by electrical activ­ ity in that structure.

170 5.4 Dualistic Versus Dual Aspect Theories

In this section I shall examine the question of whether phenomenal space is at least part of a separate entity from its neural correlate, as entailed by a dualistic ontology, or whether it is merely another aspect or attribute of it, as held by identity and dual aspect theories. In my discussion of the relative merits of dualistic and dual aspect theories, I will not enter into a digression analyzing the Aristote­ lian37 problem of the distinction between substance and attribute, and also will not reach any firm conclusion as to which theory, if either, is in fact correct. Instead, I will merely examine the relative strengths of certain arguments which can be raised on both sides of the controversy, and then investigate some of the logical implica­ tions of the dualistic alternative. I have previously noted that certain considerations from the the­ ory of evolution can be cited as constituting evidence in favor of a dual aspect theory. For instance, the theory could be invoked in order to explain the development of a postulated conscious aspect of inert matter, through the evolutionary process, into phenomenal space as it occurs in human consciousness. Thus, a dual aspect theory would not have to postulate the existence, ad hoc, of a con­ sciousness which in some manner becomes causally associated with the brain, as a dualistic theory presumably would. It would seem then that dual aspect theories are ontologically simpler than dualis­ tic theories, in the sense that they have to postulate the existence of fewer fundamentally different types of entities in the universe. However, there are also equally powerful considerations which would seem to favor a dualistic ontology. For one point, dual aspect theories would seem to have difficulties in explaining the unity of conscious experience—particularly the numerical unity of that experience over periods when consciousness is interrupted, such as during sleep—inasmuch as the physical processes with which con­ scious experience is identified by these theories would presumably also be interrupted during these periods (or else why wouldn’t we remain conscious then, in view of the postulated numerical identity between the two). While the renewed physical process might bear a qualitative identity with the interrupted process, it would be diffi­ cult to see how it could also be numerically identical. Another point in favor of a dualistic ontology along a somewhat different line involves the fact that cerebral processing takes place in parallel, rather than serially. In general, adjacent columns in

171

cerebral structures, such as the visual cortex, are not causally con­ nected together, even though, when taken as a whole, the columns may possess a topologic isomorphism with such macroscopic fea­ tures as the retinal image. Thus, the feature analysis which occurs in the visual cortex takes place on a purely local level (i. e., with each column just processing information from a small region of the ret­ ina), as Hubei and Wiesel note in the following passage. What is common to all regions is the local nature of the wiring. The information carried into the cortex by a single fiber can in principle make itself felt through the entire thickness in about three or four synapses, whereas the lateral spread, produced by branching trees of axons and dendrites, is limited for all practi­ cal purposes to a few millimeters, a small proportion of the vast extent of the cortex. The implications of this are far-reaching. Whatever any given region of the cortex does, it does locally. At stages where there is any kind of detailed systematic topogra­ phical mapping the analysis must be piecemeal. (Hubei and Wiesel, 1979, p. 152)

The foregoing point regarding parallel processing would seem to pose grave difficulties for any dual aspect theory which posited a cortical region bearing a topologic isomorphism with the retinal image as being the site of the causal determination of events in visual space, since there are no known physical phenomena, such as electrical fields, which would maintain a numerical identity over, and just over, the relevant causal gaps between columns. Still another problem for dual aspect theories positing regions of topologic isomorphism as being sites for mind body causal connec­ tions involves the fact that these sites come in pairs on opposite hemisphere of the brain, with sensory information from the left hand side of the environment being projected onto the right hemis­ phere site, and information from the right hand side of the environ­ ment being projected onto the left hemisphere site. While there are certain interhemispheric connections, notably by way of the corpus callosum, a problem would still arise for such a dual aspect theory in explaining how the information from the two sides could be inte­ grated in one unified phenomenal space. In contrast, under a dualis­ tic ontology it would be relatively easy to conceive of how a single, spatially extended, phenomenal space could bridge this hemis­ pheric gap, with the qualitative nature of points of the space corres-

172

ponding to intermediary points between the two hemispheres not being causally determined neurologically, and thus possessing a "blank” character. It can also be pointed out that the topologic difference between phenomenal space and physical entities which I analyzed earlier— namely the fact that phenomenal space is two-dimensional, whe­ reas physical entities possess at least three spatial dimensions— would be completely ad hoc under a dual aspect theory. That is, a dual aspect theory could not explain how or why phenomenal space is two-dimensional other than just by assuming it. While I do not believe that any of the foregoing arguments against dual aspect theories are conclusive, I do believe that they show that a dualistic alternative is at least worthy or serious consideration, and thus I will now turn to an examination of the details of one possible such theory. This theory holds that the mind is not only spatially extended, but also spatially coextensive (that is, possesses the same set of spatial dimensions) with physical space, and thus it constitutes a reformulation of the classical mind body problem of how events in a spatially unextended mind can be causally deter­ mined by physical events in the spatially extended brain. As I have shown, a problem arises here for the classical theory if one assumes that causes and effects must be spatially contiguous to each other. However, inasmuch as it is at least possible that a spatially extended mind could be situated so as to be spatially contiguous to a region, or a series of regions, of the brain, this particular problem can be avoided by the present theory. A new problem arises here though with regard to the question of how the mind and the body are to be differentiated (the classical answer being that the body is spatially extended while the mind is not). My solution to this prob­ lem is to hold that at least one of the differentiating characteristics between the mind and the body is topological; that the mind, one portion of which being phenomenal space, exists in a two-dimen­ sional format, whereas physical entities possess at least three spa­ tial dimensions. It should be emphasized here that I am not assert­ ing that there would be any logical inconsistency in phenomenal space being three-dimensional, like physical entities, but rather that since in fact this does not seem to be the case, it is worth at least exploring the possibility that this topologic difference may be of deep ontological significance in differentiating between the two realms.

173

It should also be pointed out that just because phenomenal space is spatially extended it does not follow that it is physical too, in the sense of being comprised by the particles and fields postulated to exist by modern physics. In fact, prima facie, phenomenal space would not seem to be comprised by these physical entities, inasmuch as they are not postulated, according to the theories of physics, to exist in a two-dimensional format. Itis true, of course, thatif “physi­ cal” is taken to mean “spatio-temporal,” then phenomenal space would be physical, but it would be illegitimate to conclude from that fact that it is in any other manner like the other spatio-temporal entities postulated to exist by modern theories of physics. Having thus cleared up an ambiguity in the word “physical,” I shall now turn to a discussion of how it may be possible for a two-dimensional phenomenal space to be so situated in the brain that events in it are spatially contiguous to the electrical activity with which they are correlated, and thus, according to the principle of the spatial contiguity of cause and effect, capable of causal con­ nections. Consider the point, discussed in Chapter Two, that it is possible for a three-dimensional space to be bounded by a twodimensional space—in fact this was shown to be the defining char­ acteristic of a three-dimensional space. Thus, it would be possible for a two-dimensional phenomenal space to “cut,” or give boundaries to, a region of three-dimensional physical space, in particular, a region, or series of regions, of the brain. It should be emphasized that such a “cut” or “bounding space” need not share any points in common with the space which it is bounding. Instead, it is possible for the two spaces to be merely spatially contiguous, since a two-dimensional phenomenal space could represent the “boundary” of an “open interval” (an interval not containing its limits) of a three-dimensional entity, such as a series of regions of the brain. Thus, in this case, phenomenal space and a series of regions of the brain would be spatially contiguous to each other and yet not share any points in common; phenomenal space being, as it were, “sandwiched” within these regions of the brain, and the possibility would thus be preserved that the two are in fact different types of entities. It would also be possible, as I sug­ gested in my model for a causal connection between events in phe­ nomenal space and electrical activity in the visual cortex, for phen­ omenal space to move with respect to these regions of the brain, since a revolving two-dimensional space can also bound a three-

174 dimensional region. The claim then would be that phenomenal space is a two-dimensional surface which either remains stationary or revolves with respect to a series of regions of the brain, and which, while not actually occupying any points of the brain occupied by physical entities, such as electrons, nevertheless passes sufficiently close to these entities so as to enter into causal relationships with them. It would seem then that a dualistic solution to the mind body problem can at least be coherently developed, even if the neurophy­ siological evidence at this point in time is insufficient as to show whether such a theory or a dual aspect alternative is in fact correct. It would also seem though that empirical evidence can be relevant for deciding this issue, as I have shown by my various physiological criteria for a neural region to constitute a site for a mind body causal connection, and thus it may be possible to decide this issue in the future.

175

FOOTNOTES TO CHAPTER ONE

1

2 3

4 5

6 7

8 9

10

11 12

See J. J. Gibson, "New Reasons for Realism,” in Synthese 17 (1967), pp. 162-177. Also see the discussion of Gibson’s position by Mary Henle in "On Naive Realism in Perception,” in Essays in Honor of James J. Gibson (Ithaca: Cornell University Press, 1974), pp. 40-56. John Austin, Sense and Sensibilia (Oxford: Oxford University Press, 1976). For an exposition of the hypothetico-deductive method see Pierre Duhem, The Aim and Structure of Physical Theory, translated by Philip Wiener (New York: Athenum, 1962); Carl Hempel, Aspects of Scientific Explanation (New York: Free Press, 1965); and Karl Popper, The Logic of Scientific Discovery (New York: Harper and Row, 1968). While Duhem tends towards a positi­ vistic view of science and thus espouses the use of the method for the discovery of mathematical laws describing experience and not for ontology, I see no reason why the use of the method cannot be extended to include the discovery of the ontological nature of the physical world, which seems to be more in line with the position of Popper, who is a dualist. Eugene Wigner, Symmetries and Reflections (Bloomington: Indi­ ana University Press, 1967). John Von Neumann, Mathematical Foundations of Quantum Mechan­ ics (Princeton: Princeton University Press, 1955). See David Bohm, Wholeness and the Implicate Order (London: Rou­ tledge and Kegan Paul, 1980). R. G. Collingwood, An Essay on Metaphysics (Oxford: Oxford Uni versity Press, 1940), pp. 313-327. David Hume, An Inquiry Concerning Human Understanding (Indi anapolis: Bobbs Merrill, 1955), Sec. 7; and A Treatiseof Human Nature (Oxford: Oxford University Press, 1888), Part III. The distinction is originally due to Galileo, and is perhaps expressed in its classical rendition best by John Locke in An Essay Concerning Human Understanding (New York: Dover Publi­ cations, 1959), Vol. 1, pp. 169-182. Wilfred Sellars, “Empiricism and the Philosophy of Mind,” in Science, Perception and Reality (London: Routledge and Ke­ gan Paul, 1963), pp. 127-196. Austin, Sense and Sensibilia, p. 8. The “cross ratio” of four points, defined as follows: (Xj-X3).(X2-X3) (Xj -X4) (X2-X4)

176

13 14 15

16 17 18

19 20 21 22 23

24 25

26

remains invariant under projection. Austin, Sense and Sensibilia. Gilbert Ryle, The Concept of Mind (New York: Barnes and Noble, 1978), pp. 35-37. See Johann Goethe. Farbenlehre, translated as Theory of Colors by Charles Eastlake (Cambridge: M.I.T. Press, 1970) and Isaac Newton, Opticks (New York: Dover Publications, 1952). A. J. Ayer, The Foundations of Empirical Knowledge (New York: Macmillan, 1940), pp. 22-24. Ryle, The Concept of Mind, p. 238. See Roderick Chisholm, Perceiving: a Philosophical Study (Ithaca: Cornell University Press, 1957), pp. 154-156; Austin, Sense and Sensibilia, p. 100; and Frank Jackson, Perception a Represen­ tative Theory (Cambridge: Cambridge University Press, 1977), pp. 15-32. Jackson, Perception a Representative Theory, pp. 15-32. Fred Dretske, Knowledge and the Flow of Information (Cambridge: M.I.T. Press, 1981), Ch. 6. Sellars, Empiricism and the Philosophy of Mind. Ludwig Wittgenstein, Philosophical Investigations, translated by G. E. M. Anscombe (New York: Macmillan, 1953), par. 269-278. Rudolf Carnap, The Logical Structure of the World, translated by Rolf A. George (Berkeley: University of California Press, 1967), Sec. 146-149. See John Wisdom, Other Minds (Berkeley: University of California Press, 1968). Ayer, The Problem of Knowledge (Harmondsworth, England: Pen­ guin Books, 1956), pp. 65, 66. See M. D. Sanders; E. Warrington; J. Marshall; and L. Wieskrantz, “Blindsight: Vision in a Field Defect,” in The Lancet (1974), pp. 707, 708.

177 FOOTNOTES TO CHAPTER TWO

1

2 3 4

5 6 7

8 9

10

11 12

13 14 15

16

17 18

19

Albert A. Blank, “Axiomatics of Binocular Vision,” in Journal of the Optical Society of America 48 (1958), pp. 328-334. George Berkeley, Alciphron, in Berkeley’s Works on Vision edited by Colin Turbayne (Indianapolis: Bobbs Merrill, 1963), Fourth Dialogue, p. 107. Thomas Reid, An Inquiry into the Human Mind (Chicago: Univer­ sity of Chicago Press, 1970), p. 128. Hermann von Helmholtz, Treatise on Physiological Optics, trans­ lated by James Southall (New York: Dover Publications, 1962), Vol. 3, Sec. 28. Carnap, The Logical Structure of the World, Sec. 80. R. B. Angell, “The Geometry of Visibles," in Nous 8 (1974), pp. 87-117. Henri Poincare, Science and Hypothesis (New York: Dover Publica­ tions, 1952), p. 53. C. D. Broad, Scientific Thought (Paterson, N.J: Littlefield, Adams and Co., 1959), pp. 290-303. William James, The Principles of Psychology, (Cambridge: Har­ vard University Press, 1981), Vol. 2, Ch. 20. Gibson, The Perception of the Visual World (Boston: Houghton Mifflin, 1950), Ch. 10. Rudolf Luneburg, “Metric Methods in Binocular Visual Percep­ tion,” in Courant Anniversary Volume (New York: Inters­ cience Publishers, 1948), p. 215. See Edward Huntington, The Continuum and Other Types of Serial Order (New York: Dover Publications, 1955). Richard Gregory, Eye and Brain (New York: McGraw-Hill, 1967), pp. 45-50. Immanuel Kant, Critique of Pure Reason, translated by Norman Kemp Smith (Toronto: Macmillan, 1929), pp. 135-169. Giuseppe Peano, “A Space Eating Curve,” in Selected Works of Giuseppe Peano, translated by Hubert Kennedy (Toronto: University of Toronto Press, 1973), pp. 143-149. Karl Menger, “What is Dimension” in American Mathematical Monthly 50 (1943), pp. 2-7. Ames’ work is summarized by Richard Gregory, The Intelligent Eye (New York: McGraw Hill, 1970), pp. 26-29. Adelbert Ames, “Visual Perception and the Rotating Trapezoidal Mirror” in Psychological Monograph 65 (1951), No. 324. See Bela Julesz, Foundations of Cyclopean Perception (Chicago: University of Chicago Press, 1971).

178

FOOTNOTES TO CHAPTER THREE 1

2 3 4 5 6 7 8 9

10

11

12

13 14 15

16 17

The only other paper which lam aware of which ascribes a variable curvature to visual space (this being in the context of a varia­ tion on the Luneburg theory) is Antonio Battro; Scipione di Pierro Netto; and Reinier Rozestraten, “Riemannian Geome­ tries of Variable Curvature in Visual Space: Visual Alleys, Horopters, and Triangles in Big Open Fields,” in Perception 5 (1976), pp. 9-23.' A. C. Ewing, A Short Commentary on Kant's Critique of Pure Rea­ son, (Chicago: University of Chicago Press, 1974), pp. 39-50. Peter Strawson The Bounds of Sense (London: Methuen, 1976), pp. 277-292. Gibson, The Perception of the Visual World, Ch. 10. Helmholtz, Physiological Optics, Vol. 3, Sec. 28. Reid, An Inquiry into the Human Mind, pp. 122-133. Norman Daniels, Thomas Reid’s Inquiry (New York: Burt Franklin and Co., 1974). Angell, 1974. Luneburg, Mathematical Analysis of Binocular Vision (Princeton: Princeton University Press, 1947); “Metric Methods in Binocu­ lar Visual Perception” in Courant Anniversary Volume; and “The Metric of Binocular Visual Space" in Journal of the Opti­ cal Society of America 40 (1950), pp. 627-642. Blank, “Axiomatics of Binocular Vision,” in Journal of the Optical Society of America 48 (1958), pp. 328-334; “LuneburgTheory of Binocular Space Perception,” in Psychology: a Study of a Science, edited by Sigmund Koch (New York: McGraw Hill, 1959), Vol. 1, pp. 395-426; and “Luneburg Theory of Binocular Vision,” in Journal of the Optical Society of America 43 (1953), pp. 717-727. James Hopkins, “Visual Geometry,” in Philosophical Review 82 (1973), pp. 3-34. Gibson, The Ecological Approach to Visual Perception (Boston; Houghton Mifflin, 1979). Angell, 1974. Graham Nerlich, The Shape of Space (Cambridge: Cambridge Uni­ versity Press, 1976). Thorne Shipley, “Convergence Function in Binocular Visual Space,” in Journal of the Optical Society of America 47 (1957), pp. 785-821. Ibid., p. 801. Wolfgang Kohler, Gestalt Psychology (New York: Liveright Pub­ lishing, 1929), Ch. 3.

179

18 19 20

21 22 23 24 25 26

27 28

29

30 31

Gibson, The Perception of the Visual World, Ch. 9. Robert Thouless, “Phenomenal Regression to the Real Object,” I, in British Journal of Psychology 21 (1931), pp. 339-359. A. S. Gilinsky, “The Effect of Attitude upon the Perception of Size,” in American Journal of Psychology 68 (1955), pp. 173-192. Luneburg, 1948, p. 239. Angell, 1974. Shipley, 1957, p. 805. M. H. Pirenne, Optics, Painting & Photography (Cambridge: Cam­ bridge University Press, 1971), pp. 145-148. David Marr, Vision (San Francisco: W. H. Freeman, 1982), pp. 277-294, Julesz, Foundations of Cyclopean Perception. Patrick Heelan, “Towards a New Analysis of the Pictorial Space of Vincent Van Gogh,” in Art Bulletin 54 (1972), pp. 478-492. Edwin Boring and D. W. Taylor, “Apparent Visual Size as a Func­ tion of Distance for Monocular Observers,” in American Jour­ nal of Psychology 55 (1942), pp. 102-105. E. L. Chalmers, “Monocular Cues in the Perception of Size and Distance,” in American Journal of Psychology 65 (1952), pp. 415-423. T. Ueno, “The Size-Distance Invariance Hypothesis and the Psy­ chophysical Law,” in Japanese Psychological Research 4 (1962), pp. 99-112. Thouless, “Phenomenal Regression to the Real Object,” II, in Brit­ ish Journal of Psychology 22 (1931), pp. 1-30.

180 FOOTNOTES TO CHAPTER FOUR

For an exposition of this subject see Stephen Kosslyn, Image and Mind (Cambridge: Harvard University Press, 1980). Maurice Merleau-Ponty, The Phenomenology of Perception, trans­ 2 lated by Colin Smith (london: Routledge and Kegan Paul, 1966); and Signs, translated by Richard McLeary (Evanston: Northwestern University Press, 1968). Berkeley, Essay Towards a New Theory of Vision, in Works on 3 Vision, par. 45. 4 Locke, An Essay Concerning Human Understanding. Vol. 1, p. 186. 5 Berkeley Essay Towards a New Theory of Vision, par. 132-136. 6 Michael Morgan, Molyneux’s Question (Cambridge: Cambridge University Press, 1977), pp. 158-208. Rene Descartes, Optics, in Discourse on Method, Geometry and 7 Meteorology, translated by Paul Olscamp (Indianapolis: Bobbs Merrill, 1965), Sixth Discourse, p. 101. 8 Ryle, The Concept of Mind. p. 213. 9 D. M. Armstrong, Berkeley's Theory of Vision (Melbourne: Mel­ bourne University Press, 1960), p. 213. 10 Gibson, ThePerceptionof the Visual World, p.54. Gibson makes the following argument there: “If the retinal image were really a picture there would have to be another eye behind the eye with which to see it. The notion that we see our retinal images is based on some such idea as a little seer sitting in the brain and looking at them. The question which then arises is how he can see it.” 11 See Descartes’ discussion of physiological optics in his Optics, and his discussion of the relation of the pineal gland to the mind body problem in The Passions of the Soul, in Philosophical Works of Descartes, translated by Elizabeth Haldane and G. R. T. Ross (Cambridge: Cambridge University Press, 1911). 12 Berkeley, New Theory of Vision, par. 14.

1

181

FOOTNOTES TO CHAPTER FIVE

1 2

3

4

5

6 7

8 9 10

11 12

13

14

15

Abner Shimony, “Perception from an Evolutionary Point of View,” in Journal of Philosophy 19 (1971), pp. 571-583. Donald Campbell, "Evolutionary Epistemology,” in The Philo­ sophy of Karl Popper edited by Paul Schilpp (La Salle: Open Court, 1974), Vol. 1, pp. 413-463. Herbert Feigl, The Mental and the Physical (Minneapolis: Univer­ sity of Minnesota Press, 1967). Nicholas Malebranche, De la Recherche de la Verite, translated by Thomas Lennon and Paul Olscamp (Columbus: Ohio State University Press, 1980). See Leibniz, Discourse on Metaphysics (Manchester: Manchester University Press, 1953), p. 34. There, Leibniz argues for this point as follows: “For the effect must correspond to its cause, and it is even best known by knowledge of its cause, and it is unreasonable to introduce a sovereign intelligence ordering all things and then, instead of using his wisdom, only to use the properties of matter to explain the phenomena." Hume, A Treatise of Human Nature, p. 173. See the discussions of Bernard d’Espagnat, Conceptual Founda­ tions of Quantum Mechanics, Second Edition (Reading: W. A. Benjamin, 1976), pp. 75-95; and Bohm, Wholeness and the Implicate Order. Kant, Critique of Pure Reason, pp. 152-160. Descartes, Philosophical Works of Descartes, Vol. 2, p. 231. See Leibniz’ discussion in Principles of Nature and of Grace in Leibniz Philosophical Writings, edited by G. H. R. Parkinsoi (London: J. M. Dent and Sons, 1973), pp. 195-204. Gibson, The Ecological Approach to Visual Perception, Ch. 12. R. G. Robson, “Receptive Fields: Neural Representation of the Spa tial and Intensive Attributes of the Visual Image,” in Hand­ book of Perception, Vol. 5, Seeing, edited by Edward Carterette and Morton Friedman (New York: Academic Press, 1975), pp. 81-116. Peter Schiller and Joseph Malpeli, “Functional Specificity of Lat­ eral Geniculate Laminae of the Rhesus Monkey,” in Journal of Neurophysiology 41 (1978),pp. 788-797. Eric Schwartz, “Computational Anatomy and Functional Architec­ ture of Striate Cortex: a Spatial Mapping Approach to Percep­ tual Coding” in Vision Research 20 (1980), pp. 645-669. David Hubei and Torsten Wiesel, "Brain Mechanisms of Vision, in Scientific American 241 (1979), pp. 150-162.

182 16

17 18

19 20 21 22 23

24 25

26

27

28

29 30

31

32

Hubei and Wiesel, “Uniformity of Monkey Striate Cortex: a Parallel Relationship between Field Size, Scatter, and Magnification Factor,” in Journal of Comparative Neurology 158 (1974), pp. 295-306/ Hubei and Wiesel, 1979, p. 152. Shimon Ullman. The Interpretation of Visual Motion (Cambridge: M.I.T. Press, 1979). Marr, Vision, Ch. 3. Julesz, Foundations of Cyclopean Vision, Ch. 3. Marr, Vision, pp. 111-152. See Colin Blakemore, “The Representation of Three-dimensional Visual Space in the Cat’s Striate Cortex,” in Journal of Physi­ ology 209 (1970), pp. 155-178. See G. F. Poggio and B. Fischer, “Binocular Interaction and Depth Sensitivity in Striate and Prestriate Cortex of Behaving Rhe­ sus Monkey,” in Journal of Neurophysiology 40 (1977), pp. 1392-1405. P. G. H. Clarke; I. M. L. Donaldson; and D. Whitteridge, “Binocular Visual Mechanisms in Cortical Areas I and II of the Sheep,” in Journal of Physiology 256 (1976),pp. 509-526. E. G. Jones and T. P. S. Powell, “An Anatomical Study of Converg­ ing Sensory Pathways within the Cerebral Cortex of the Mon­ key” in Brain 93 (1970), pp. 793-820. Also see Gerald Schneider, “Two Visual Systems,” in Science 53 (1969), pp. 895-902. Charles Bruce; Robert Desimone; and Charles Gross, “Visual Prop­ erties of Neurons in a Polysensory Area in Superior Temporal Sulcus of the Macaque,” in Journal of Neurophysiology 46 (1981), pp. 369-384. Wilder Penfield and Herbert Jasper, Epilepsy and the Functional Anatomy of the Human Brain (Boston: Little Brown, 1954). Also see Penfield, The Mystery of the Mind (Princeton: Prin­ ceton University Press, 1975). Leo Chapula and Robert Rhoades, “Responses of Visual, Somato­ sensory, and Auditory Neurons in the Golden Hamster’s Superior Colliculus,” in Journal of Physiology 270 (1977). N. K. Humphrey, “Vision in a Monkey without Striate Cortex: a Case Study,” in Perception 3 (1974), pp. 241-255. Kohler, The Place of Value in a World of Facts (New York: Mentor Books, 1966), Ch. 6. Karl Pribram, Languages of the Brain: Experimental Paradoxes and Principles in Neuropsychology (Englewood Cliffs: Pre­ ntice Hall, 1971), pp. 110-115. Marr, Vision, Ch. 4.

183

33

34

35

36

37

J. Davidoff and B. Wilson, “A Case of Visual Agnosia Showing a Disorder of Pre-Semantic Visual Classification,” in Cortex 21 (1985), pp. 121-134. V. B. Mountcastle, “Modality and Topographic Properties of Single Neurones of Cat’s Somatic Sensory Cortex,” in Journal of Neu­ rophysiology 20 (1957), pp. 408-434. Also see Penfield and Jasper, Epilepsy and the Functional Anatomy of the Human Brain. Experiments are discussed there where the human somatic cortex is electrically stimulated and where tactile sen­ sations are experienced in the corresponding regions of the body. See H. L. Teuber; W. S. Battersby; and M. B. Bender, Visual Field Defects after Penetrating Missile Wound of the Brain (Cam­ bridge: Harvard University Press, 1960). M. R. Harter; C. Aine; and C. Schroeder, “Hemispheric Differences in Event-Related Potential Measures of Selective Attention, in Brain and Information: Event-Related Potentials, edited by Rathe Karrer, Jerome Cohen, and Patricia Tueting(New York. New York Academy of Sciences, 1984), pp. 210-211. Aristotle, Categories, Metaphysics, Book Z.

BIBLIOGRAPHY Abbott, Edwin, Flatland: A Romance of Many Dimensions (New York: Dover Publications, 1952). Abbott, Thomas K., Sight and Touch: An Attempt to Disprove the Received (or Berkeleian) Theory of Vision (London: Longman, Green, Longman, Longman, Roberts, and Green, 1864). Ames, Adelbert Jr., “Visual Perception and the Rotating Trapezoi­ dal Mirror,” in Psychological Monograph, 65 (1951), No. 324. "The Geometry of Visibles,” in Nous 8 (1974), pp.

Aristotle, The Basic Works of Aristotle, edited by Richard McKeon (New York: Random House, 1941). Armstrong, D. M., Berkeley’s Theory of Vision (Melbourne: Mel­ bourne University Press, 1960). Austin, John, Sense and Sensibilia (Oxford: Oxford University Press, 1976). Ayer, A. J., The Foundations of Empirical Knowledge (London: Macmillan & Co., 1958). 'Ihe Problem of Knowledge (Harmondsworth, England: Penguin Books, 1957). Baird, John, Psychophysical Analysis of Visual Space (Oxford: Pergamon Press, 1970). Battro, Antonio; di Pierro Netto, Scipione; and Rozestraten, Reinier, Riemannian Geometries of Variable Curvature in Visual Space: Visual Alleys, Horopters, and Triangles in Big Open Fields,” in Perception 5 (1976), pp. 9-23. Berkeley, George, Works on Vision, edited by Colin Turbayne (Indi­ anapolis: Bobbs Merrill, 1963). Blakemore, Colin, “The Representation of Three-dimensional Vis­ ual Space in the Cat’s Striate Cortex,” in Journal of Physiology 209(1970), pp. 155-178. Blank, Albert A., “Axiomatics of Binocular Vision,” in Journal of „ the Optical Society of America 48 (1958), pp. 328-334. Luneburg Theory of Binocular Space Perception,” in Psychology: a Study of a Science, edited by Sigmund Koch (New York: McGraw-Hill, 1959), Vol. 1. Luneburg Theory of Binocular Vision,” in Journal of the Optical Society of America 43 (1953), pp. 717-727.

186 Bohm, David, Wholeness and the Implicate Order (London: Rou­ tledge and Kegan Paul, 1980). Bohr, Neils, Atomic Physics and Human Knowledge (London: Rou­ tledge and Kegan Paul, 1980). Boring, Edwin, Sensation and Perception in the History of Experi­ mental Psychology (New York: D. Appleton—Century Co., 1942). Boring, Edwin and Taylor, D. W., “Apparent Visual Size as a Func­ tion of Distance for Monocular Observers,” in American Jour­ nal of Psychology 55 (1942), pp. 102-105. Broad, C. D. The Mind and its Place in Nature (London: Routledge & Kegan Paul Ltd., 1968). Scientific Thought (Paterson, N.J: Littlefield, Adams & Co., 1959). Bruce, Charles; Desimone, Robert; and Gross, Charles, “Visual Properties of Neurons in a Polysensory Area in Superior Tem­ poral Sulcus of the Macaque,” in Journal of Neurophysiology 46 (1981), pp. 369-384. Campbell, Donald, “Evolutionary Epistemology,” in The Philo­ sophy of Karl Popper, edited by Paul Schilpp (La Salle, II: Open Court, 1974), Vol. 1., pp. 413-463. Carlson, V. R., “Overestimation in Size-Constancy Judgments,” in American Journal of Psychology 65 (1952), pp. 415-423. Carnap, Rudolf, The Logical Structure of the World, translated by Rolf A. George (Berkeley: University of California Press, 1967). Chalmers, E. L. Jr., “Monocular Cues in the Perception of Size and Distance,” in American Journal of Psychology 65 (1952), pp. 415-423. Chapula, Leo and Rhoades, Robert, “Responses of Visual, Somatos­ ensory, and Auditory Neurons in the Golden Hamster’s Super­ ior Colliculus,” in Journal ofPhysiology 270 (1977), pp. 595-626. Chisholm, Roderick, Perceiving: A Philosophical Study (Ithaca: Cornell University Press, 1957). Clarke, P. G. H.; Donaldson, I. M. L.; and Whitteridge, D., “Binocu­ lar Visual Mechanisms in Cortical Areas I and II of the Sheep,” in Journal of Physiology 256 (1976), pp. 509-526. Collingwood, R. G., An Essay on Metaphysics (Oxford: Oxford Uni­ versity Press, 1940). Craig, E. J., “Phenomenal Geometry,” in British Journal for the Philosophy of Science 20 (1969), pp. 121-135.

187

Daniels, Norman, Thomas Reid’s Inquiry (New York. Burt Franklin & Co., 1974). . „, . Davidoff, J., and Wilson, B„ “A Case of Visual Agnosia Showing a Disorder of Pre-Semantic Visual Classification, in or ex (1985), pp. 121-134. , Descartes, Rene, Discourse on Method, Optics, Geome ry an Meteorology, translated by Paul Olscamp (Indianapolis: Bobbs Merrill 1965). . , u ,, Philosophical Works of Descartes, translated by Elizabeth Haldane and G. R. T. Ross (Cambridge: Cambridge University Press, 1911). „ , D’Espagnat, Bernard, Conceptual Foundations ofQuantum Mechan­ ics, Second Edition (Reading: W. A. Benjamin, 1976). Dretske, Fred, Knowledge and the Flow of Information, am bridge: M.I.T. Press, 1981). Duhem, Pierre, The Aim and Structure of Physical Theory, trans­ lated by Philip Wiener (New York: Athenum, 1962). Eccles, John, Facing Reality: Philosophical Adventures of a brain Scientist (New York: Springer, 1970). Einstein, A.; Podolsky, B.; and Rosen. N„ “Can Quantum Mechani­ cal Description of Physical Reality be Considered Complete, in Physical Review 47 (1935), pp. 777-780. Epstein, William, “Attitudes of Judgment and the Size-Distance Invariance Hypothesis,” in Journal of Experimental bsycnoiogy 66(1963), pp. 78-83. , n ■ Euclid, Optics, translated by Harry Burton, in Journal of e cal Society of America 35 (1945), pp. 357-372. Ewing, A. C„ A Short Commentary on Kant’s Critique of bare Reason (Chicago: University of Chicago Press, 19 )• Feigl, Herbert, The Mental and the Physical (Minneapolis, n sity of Minnesota Press, 1967). • • French, Robert, “The Geometry of Visual Space, fort com

Gibson, J. J„ The Ecological Approach to Visual Perception (Bos­ ton: Houghton Mifflin, 1979). 162-172 “New Reasons for Realism,” in Synthese 17 (1967), PPlyiiffiin The Perception of the Visual World (Boston: Houg on The Senses Considered as Perceptual Systems (Boston. Ho g Mifflin, 1967).

188 Gilinsky, A. S., “The Effect of Attitude upon the Perception of Size,” in American Journal of Psychology 68 (1955), pp. 173-192. Goethe, Johann, Farbenlehre, translated as Theory of Colors by Charles Eastlake (Cambridge: M.I.T. Press, 1970). Goodman, Nelson, Languages of Art (Indianapolis: Hackett, 1976). Gregory, Richard, Eye and Brain (New York: McGraw-Hill, 1967). The Intelligent Eye (New York: McGraw-Hill, 1970). Hamilton, Sir William, Lectures on Metaphysics and Logic (Edin­ burgh: William Blackwood and Sons, 1877). Hardy, LeGrand; Rand, Gertrude; Rittler, Catherine; Blank, A. A.; and Boeder, Paul, The Geometry of Binocular Space Percep­ tion, (New York: Knapp Memorial Laboratories of Columbia College of Physicians and Surgeons, 1953). Harter, M. R.; Aine, C.; and Schroeder, C., “Hemispheric Differences in Event-Related Potential Measures of Selective Attention,” in Brain and Information: Event-Related Potentials, edited by Rathe Karner, Jerome Cohen, and Patricia Tueting (New York: New York Academy of Sciences,) Heelan, Patrick, Space-Perception and the Philosophy of Science (Berkeley: University of California Press, 1983). “Towards a New Analysis of the Pictorial Space of Vincent Van Gogh,” in Art Bulletin 54 (1972), pp. 478-492. Hegel, G. W. F., Hegel’s Logic, translated by William Wallace (Oxford: Oxford University Press, 1975). Helmholtz, Hermann von, Treatise on Physiological Optics, trans­ lated by James Southall (New York: Dover Publications, 1962). Hempel, Carl, Aspects of Scientific Explanation (New York: Free Press, 1965). Henle, Mary, “On Naive Realism” in Essays in Honor of James J. Gibson (Ithaca: Cornell University Press, 1974), pp. 40-56. Holmes, G., “The Organization of the Visual Cortex,” in Proceed­ ings of the Royal Society B, 132 (1945), pp. 348-361. Hopkins, James, “Visual Geometry,” in Philosophical Review 82 (1973), pp. 3-34. Hubei, David and Wiesel, Torsten, “Brain Mechanisms of Vision,” in Scientific American 241 (1979), pp. 150-162. “Stereoscopic Vision in Macaque Monkey,” in Nature 225 (1970), pp. 41,42. “Uniformity of Monkey Striate Cortex: a Parallel Relationship between Field Size, Scatter, and Magnification Factor,” in Journal of Comparative Neurology 158 (1974), pp. 295-306.

189 Hume, David, An Inquiry Concerning Human Understanding (New York: C. W. Hendel, 1955). A Treatise of Human Nature (Oxford: Oxford University Press 1888). Humphrey, N. K., “Vision in a Monkey without Striate Cortex: a Case Study,” in Perception 3 (1974), pp. 241-255. Huntington, Edward, The Continuum and Other Types of Serial Order (New York: Dover Publications, 1955). Husserl, Edmund, Ideas: General Introduction to Pure Phenome­ nology, translated by W. R. Boyce Gibson (London: Collier— Macmillan Ltd., 1969). Ittelson, William, Visual Space Perception (New York: Springer, 1960). Jackson, Frank, Perception a Representative Theory (Cambridge: Cambridge University Press, 1977). James, William, The Principles of Psychology (Cambridge: Har­ vard University Press, 1981). Jones, E. G. and Powell, T. P. S. “An Anatomical Study of Converg­ ing Sensory Pathways within the Cerebral Cortex of the Mon­ key,” in Brain 93 (1970), pp. 793-820. Julesz, Bela, Foundations of Cyclopean Perception (Chicago: Uni­ versity of Chicago Press, 1971). Kant, Immanuel, Critique of Pure Reason, translated by Norman Kemp Smith (Toronto: Macmillan, 1929). The Metaphysical Foundations of Natural Science, translated by James Ellington (Indianapolis: Bobbs Merrill, 1970). Koffka, Kurt, “Some Problems of Space Perception,” in Psycholo­ gies of 1930, edited by Carl Murchison and Carl Allanmore (Worcester: Clark University Press, 1930). Kohler, Wolfgang, Gestalt Psychology (New York: Liveright Pub­ lishing, 1947). The Place of Value in a World of Facts (New York: Mentor Books, 1966). Kosslyn, Stephen, Image and Mind (Cambridge: Harvard Univer­ sity Press, 1980). Kruger, L., “The Topography of the Visual Projection to the Mesencephalon: a Comparative Survey,” in Brain, Behavior and Evolution 3 (1970), pp. 169-177. Lenauer, A. A., “The Effect of Viewing Conditions and Instructions on Shape Judgments,” in British Journal of Psychology 55 (1964), pp. 49-57.

190

Leibniz, Gottfried, Discourse on Metaphysics, translated by Peter Lucas and Leslie Grint (Manchester: Manchester University Press, 1953). Philosophical Writings, edited by G. H. R. Parkinson (London: J. M. Dent & Sons, 1979). Leibowitz, H. W. and Harvey, Lewis, “Effect of Instructions, Envir­ onment, and Type of Test Object on Matched Size,” in Journal of Experimental Psychology 81 (1969), pp. 36-43. Locke, John, An Essay Concerning Human Understanding (New York: Dover Publications, 1959). Lucas, J. R. “Euclides ab Omni Naevo Vindictas,” in British Jour­ nal of the Philosophy of Science 20(1969), pp. 1-11. Luneburg, Rudolf, Mathematical Analysis of Binocular Vision (Princeton: Princeton University Press, 1947). “Metric Methods in Binocular Visual Perception,” in Courant Anniversary Volume (New York: Interscience Publishers, 1948), pp. 215-239. “The Metric of Binocular Visual Space,” in Journal of the Optical Society of America 40 (1950), pp. 627-642. Mach, Ernst, The Analysis of Sensations (New York: Dover Publi­ cations, 1959). Space and Geometry, translated by Thomas McCormack (La Salle, IL: Open Court, 1960). Mackie, J. L., “Causes and Conditions,” in American Philosophical Quarterly 2 (1965), pp. 245-264. The Cement of the Universe; a Study of Causation (Oxford: Oxford University Press, 1974). Malebranche, Nicolas, De la Recherche de la Verite, translated by Thomas Lennon and Paul Olscamp (Columbus: Ohio State University Press, 1980). Marr, David, Vision (San Francisco: W. H. Freeman, 1982). Menger, Karl “What is Dimension,” in American Mathematical Monthly 50 (1943), pp. 2-7. Merleau-Ponty, Maurice, The Phenomenology of Perception, trans­ lated by Colin Smith (London: Routledge & Kegan Paul, 1966). Signs, translated by Richard McLeary (Evanston: Northwestern University Press, 1968). The Visible and the Invisible, translated by Alphonso Lingin (Evanston: Northwestern University Press, 1968).

191

Monck, W. H. S., Space and Vision (Dublin: William McGee, 1872). Moore, G. E., Philosophical Papers (London: George Allen & Unwin, 1977). Morgan, Michael, Molyneux's Question (Cambridge: Cambridge University Press, 1977). Mountcastle, V. B., “Modality and Topographic Properties of Single Neurones of Cat’s Somatic Sensory Cortex” in Journal of Neu­ rophysiology 20 (1957), pp. 408-434. Nerlich, Graham, The Shape of Space (Cambridge: Cambridge Uni­ versity Press, 1976). Newton, Isaac, Opticks (New York: Dover Publications, 1952). Pastore, Nicholas, Selective History of Theories of Visual Percep­ tion 1650-1950 (Oxford: Oxford University Press, 1971). Peano, Giuseppe, “A Space Eating Curve,” in Selected Works of Giuseppe Peano, translated by Hubert Kennedy (Toronto: University of Toronto Press, 1973), pp. 143-149. Penfield, Wilder The Mystery of the Mind (Princeton: Princeton University Press, 1975). Penfield, Wilder and Jasper, Herbert, Epilepsy and the Functional Anatomy of the Human Brain (Boston: Little Brown, 1954). Pirenne, M. H., Optics, Painting & Photography (Cambridge: Cam bridge University Press, 1971). Poggio, G. F., and Fischer, B., “Binocular Interaction and Depth Sensitivity in Striate and Prestriate Cortex of Behaving Rhe­ sus Monkey,” in Journal of Neurophysiology 40 (1977), pp. 1392-1405. Poincare, Henri, Dernieres Pensees, translated by John Bolduc (New York: Dover Publications, 1963). Science and Hypothesis (New York: Dover Publications, 1952). Politz, Alfred, “On the Origin of Space Perception,” in Philosophy and Phenomenological Research, 1979), pp. 258-264. Popper, Karl, The Logic of Scientific Discovery (New York: Springer International, 1959). Popper, Karl and Eccles, John, The Self and Its Brain (New York: Springer International, 1977). Pribram, Karl, Languages of the Brain: Experimental Paradoxes and Principles in Neuropsychology (Englewood Cliffs: Pre­ ntice Hall, 1971). Price, H. H., Perception (London: Methuen, 1950).

192

Reid, Thomas, Essays on the Intellectual Powers of Man (Cam­ bridge: M.r.T. Press, 1969). An Inquiry into the Human Mind (Chicago: University of Chicago Press, 1970). Riggs, Lorrin, “Electrophysiology of Vision,” in Vision and Visual Perception, edited by CLarence Graham (New York: John Wiley and Sons, 1965, pp. 81-131. Robson, R. G., Receptive Fields: Neural Representation of the Spa­ tial and Intensive Attributes of the Visual Image, in Handbook of Perception, Vol. 5, Seeing, edited by Edward Carterette and Morton Friedman (New York: Academic Press, 1975), pp. 81-116. Russell, Bertrand, An Analysis of Mind (London: George Allen & Unwin, 1971). An Inquiry into Meaning and Truth (London: George Allen & Unwin, 1940). Our Knowledge of the External World (London: George Allen & Unwin,-1972). Ryle, Gilbert, The Concept of Mind (New York: Barnes & Noble, 1978). Sanders, M. D.; Warrington, E.; Marshall, J.; and Wieskrantz, L., “Blindsight: Vision in a Field Defect,” in The Lancet (1974), p. 707. Schiller, Peter and Malpeli, Joseph, “Functional Specificity of Lat­ eral Geniculate Laminae of the Rhesus Monkey,” in Journal of Neurophysiology 41 (1978), pp. 788-797. Schneider, Gerald, “Two Visual Systems,” in Science 63 (1969), pp. 895-902. Schwartz, Eric, “Computational Anatomy and Functional Archi­ tecture of Striate Cortex: A Spatial Mapping Approach to Per­ ceptual Coding,” in Vision Research 20 (1980), pp. 645-669. Sellars, Wilfred, Science, Perception and Reality (London: Rou­ tledge and Kegan Paul, 1963). Sherrington, Charles, The Integrative Action of the Nervous Sys­ tem, Second Edition (New Haven: Yale University Press, 1944). Shimony, Abner, “Perception from an Evolutionary Point of View,” in Journal of Philosophy 19 (1971), pp. 571-583. Shipley, Thorne, “Convergence Function in Binocular Visual Space,” in Journal of the Optical Society of America Al (1957), pp. 785-821.

1

193

Strawson, Peter, The Bounds of Sense (London: Methuen, 1976). Teuber, H. L.; Battersby, W. S.; and Bender, M. B„ Visual Field Defects after Penetrating Missile Wounds of the Brain (Cam­ bridge: Harvard University Press, 1960). Thouless, Robert, “Phenomenal Regression to the Real Object,” I and II, in British Journal of Psychology 21 (1931), pp. 339-359; and 22 (1931), pp. 1-30. Thrane, Gary, “Berkeley’s Proper Object of Vision,” in Journal of the History of Ideas 38 (1977), pp. 243-260. Turbayne, Colin, The Myth of Metaphor (Columbia: University of South Carolina Press, 1970). Ueno, T., “The Size-Distance Invariance Hypothesis and the Psy­ chophysical Law,” in Japanese Psychological Research 4 (1962), pp. 99-112. Ullman, Shimon, The Interpretation of Visual Motion, (Cambridge: M.I.T. Press, 1979). Von Neumann, John, Mathematical Foundations of Quantum Mechanics (Princeton: Princeton University Press, 1967). Warnock, G. J., Berkeley (Harmondsworth, England: Penguin Books, 1969). Whitehead, Alfred North, Process and Reality, Corrected Edition (New York: Macmillan, 1978). Wigner, E. P., Symmetries and Reflections (Bloomington: Indiana University Press, 1967). Wisdom, John, Other Minds (Berkeley: University of California Press, 1968). Wittgenstein, Ludwig, Philosophical Investigations, translated by G. E. M. Anscombe (New York: Macmillan, 1953).

Peter J. Hadreas

IN PLACE OF THE FLAWED DIAMOND An Investigation of Merleau-Ponty’s Philosophy American University Studies: Series V (Philosophy). Vol. 13 ISBN 0-8204-0211-7 185 pages hardback US $ 30.30*

*Recommended price - alterations reserved

In Place of the Flawed Diamond offers a survey and comparative study of Merleau-Ponty philosophy. In Peter Hadreas’ view, Merleau-Ponty’s is influenced primarily by Husserl, Sartre and Heidegger. But the sources of Merleau-Ponty’s thought cannot be circumscribed by an «intellectual narrative» which depicts his thought as an inheritance from celebrated intellec­ tual forebears. Hadreas shows how Merleau-Ponty’s thought differs from Husserl’s, Sartre’s and Heidegger’s. The issues Hadreas discusses include Merleau-Ponty’s revision of Gestalt psychology, his theory of the body-subject, and his posthumously published doctrines of the «flesh» and the chiasm. These last two issues, in particular, are contrasted with issues in Heidegger’s later philosophy.

This book gives a comprehensive reading of Merleau-Ponty’s philosphical work from The Structure of Behavior to The Visible and Invisible. It brings out clearly the continuities in Merleau-Ponty’s thought and thereby casts much needed light on the, at first sight, strange new language and problems of Merleau-Ponty’s last work. (Hubert L. Dreyfus, University of California, Berkeley).

PETER LANG PUBLISHING, INC. 62 West 45th Street USA - New York, NY 10036

Subhash C. Kak

THE NATURE OF PHYSICAL REALITY American University Studies: Series V (Philosophy). Vol. 17 ISBN 0-8204-0310-5 159 pp. hardback US $ 35.90*

*Recommended price - alterations reserved

This book is a study of the paradoxes that underlie our understanding of the physical world. It is shown that many of these paradoxes are actually variants of classical paradoxes known to the ancient Indians and Greeks. T e °° presents a historical perspective on the development of key scienti ic i eas, and discusses the significance of our understanding the nature o conscious ness in further advance. The book also examines several philosophical issues at the basis of modern physics.

Contents: Presents a review of modern physics.

PETER LANG PUBLISHING, INC. 62 West 45th Street USA - New York, NY 10036

I

Richard, H. Schlagel

FROM MYTH TO THE MODERN MIND A Study of the Origins and the Growth of Scientific Thought Volume I: Animism to Archimedes

)

American University Studies: Series V (Philosophy). Vol. 12 * ISBN 0-8204-0219-2 281 pp. hardback US $ 30.00

*Recommended price - alterations reserved

Written before the collapse of the research program of the logical posi­ tivists and the resurgent interest in the development of scientific thought as exemplified in analyses of actual historical transitions, this book is unique in undertaking to elucidate the cognitive developments and their causes underlying the history of science. Beginning with a description of forms of primitive mentality, as exemplified historically in the earlier animistic, mytho­ poetic, and theogonic traditions, the present volume identifies the transfor­ mations in the thought processes inherent in the emergence and the growth of scientific rationalism from the Presocraties thought Plato and Aristotle to Archimedes, the culminating scientific figure in the ancient world.

Contents: The purpose of the present volume is to contrast scientific ration­ alism with the earlier animistic, mythopoetic, and theogonic traditions, trac­ ing the origins and the growth of scientific thought in the works of the Presocraties, Plato and Aristotle, to Archimedes.

PETER LANG PUBLISHING, INC. 62 West 45th Street USA - New York, NY 10036

This book focuses on the philosophy of perception with particular emphasis on the geometry of phenomenal visual space and mind body issues concerning the relationships between that space and neural activity in the brain. The contents include a detailed attack on naive realism and defense of the causal theory of perception, along with analyses of both the topology and metric structure of visual space. It is shown how a variable curvature geometry for visual space can account for phenomenal visual depth perception, and an extension of that analysis is given to the other sense systems. The final chapter defends the claim that the conscious mind is a spatial entity, but still questions whether a physicalist reduction can be made of it to activity in the brain.

Robert E. French is a research fellow with Boston University’s Center for the Philosophy of Science and is Assistant Professor of Philosophy at Central Michigan University, in Mt. Pleasant, Michigan. He previously served as Assistant Professor of Philos­ ophy at Augustana College, in Rock Island, Illinois. He has published in the philosophy of geometry and the geometry of visual space in Philosophical Studies and Nous. He received his Ph.D. from Boston University and his A.B. from Dartmouth

College.