Some Gibsonian perspectives on the ways that psychologists use physics

Acta Psychologica 52 (1982) 147- 163

North-Holland Publishing Company

147

SOME GIBSONIAN PERSPECTIVES ON THE WAYS THAT PSYCHOLOGISTS USE PHYSICS

Stephen WILCOX *

Franklin & MarshaN College, USA

David A. EDWARDS

University of Georgia, USA

Accepted June 1982

The paper begins with a discussion of the influence of physics upon psychology. It is argued that physics has provided psychology both with a role model and with an ontology. Both of these roles

are criticized, and it is suggested that this relationship between physics and psychology is

maintained by an “absolutist” view of physics. The following sections are attempts to undermine

this view. First the philosophical arguments against taking physics as the description of an

epistemically independent reality are presented. Next it is demonstrated that even within physics

there are various alternative descriptions of reality. Finally, Gibson’s notion of an “ecological

physics” is briefly discussed.

[The traditional approach] had determined its psychology from a dogmatically presupposed ontology, instead of getting at its ontology from a critical examination of the nature and contents

of consciousness, as its standpoint required.

(John Dewey 1886/1973: 117)

One of the central themes of J.J. Gibson’s writings is that psychology must escape from the shadow of physics (e.g., Gibson 1961, 1979). He called for the development of an “ecological physics”, i.e., a description of the physical world relevant to the particular problems of psychology. The purpose of this paper is to explore this idea of Gibson’s. We begin with a discussion of the roles physics has played within psychology and some of the problems caused by this relationship with physics. This is

* Mailing address: S. Wilcox, Dept. of Psychology, Franklin & Marshall College, Lancaster, PA

17604. USA.

0001-69 1 S/82/0000-0000/$02.75 0 1982 North-Holland

followed by our proposal that the psychologist’s reliance upon physics is due to the pervasive view that physics describes reality “as it really is”. Finally, we attempt to undermine this view.

The influence of physics has been felt by the psychologist in two different, though related, ways: as a role model and as an ontology. We will discuss each of these in turn.

Physics as a role model

A perusal of the early textbooks in psychology reveals a conscious desire on the part of the founders of psychology to pattern the young science after the physical sciences. Although they admitted that the subject matter of psychology is different from that of physics, the early psychologists freely imported methods, modes of explanation, and even specific concepts from the physical sciences.

For example, Herbart ( 189 l), although eschewing experimental methods, made use of many ideas from physics, as the following quotes indicate.

“Concepts become forces when they resist one another” (1891: 9). “The statics and mechanics of the mind have to do with the

calculation of the equilibrium and movement of the concepts” (1891: 10).

“Between several dissimilar simple essences exists a relation which, with the help of a comparison from the physical world, may be described as pressure and resistance” (1891: 120).

Wundt, who is usually credited with the establishment of psychology as an experimental science, gives the impression in his Lectures on Human and Animal Psychology that he was especially influenced by physics. In the introduction to that volume he recounts a series of success stories from the physical sciences and then proclaims, “Let us now apply experiment to the science of the mind” (Wundt 1894: 10).

Titchener (1900: 34-35) provides another example: “We may com- pare sensation, the element of the idea, to the elements treated in chemical science. The idea is a compound; it consists of a number of elemental processes”.

More recent instances of importations from physics are not hard to find. Indeed, almost every school of psychology offers examples, from Freud’s hydraulic analogies to the field theory of the Gestaltists to the

S. Wilcox, D.A. Edwards / Physics and psych&~ 149

hologram model of Karl Pribram. A particularly striking modern example is the theory of motivation proposed by Atkinson and Birch (1970). Their book The Dynamics of Action lays out a system which is superficially very similar to classical dynamics. For example, one of their basic principles is that “a behavioral tendency, once it has been aroused, will persist in its present state until acted on by some force that either increases or decreases its strength” (1970: 10). Cf., Newton’s first law of motion: “Every body continues in its state of rest or of uniform motion in a right line, unless it is compelled to change that state by forces impressed upon it”.

Another dimension to the phenomenon is represented by the fre- quent attempts to justify various positions by comparisons with physics. The idea seems to be that psychology is on the right track to the degree that it resembles physics. A particularly important example is Chom- sky’s (1959) review of Skinner’s Verbal Behavior in which he uses analogies from physics to claim that Skinner’s program is not really scientific.

Now, although the use of physics as a role model may sometimes be fruitful, it has often led to pernicious results such as the view that mental phenomena are made up of “elements”. This cannot be wholly blamed upon the attempt to copy physics, given that the idea goes back to the Greeks. However, it seems likely in light of some of the passages we have quoted that the idea has been maintained by psychology’s awe of physics. In any case, no viewpoint has ever been kept alive so long with so little evidence as the belief that the mind consists of atomic elements.

The nineteenth century introspectionists were undaunted by the fact that people report seeing tables and chairs rather than patches of color. They simply trained observers to see things their way. Titchener (1909), for example, warned of the “stimulus error”, the conflation of the “immediate objects of consciousness” with our experiences of the external world: “We live so habitually in a world of objects, and we think so habitually in terms of common sense, that it is difficult for us to take up the psychological standpoint towards intensity of sensation, and to look at consciousness as it is, apart from any objective reference” (1909: 202).

This relatively heavy-handed approach gave way in this century to the method (which had also been used earlier) of putting people in situations where the “elements” are all that is available (e.g., dark rooms with point sources of light).

150 S. Wikox, D.A. Edwurds / Ph.vsrcs and psyhologt

Likewise, contemporary information processors use reaction time measures to “discover” the chain of subprocesses which supposedly take place too fast to detect under normal circumstances. The information processing viewpoint is an interesting case in point. The basic program amounts to the analysis of mental processes into constitutents which (at least in principle) can be programmed in a computer [ 11. On the surface of it, it is difficult to see what we gain by beginning with, for example, seeing and breaking it down into subcomponents. We all know what it means to see, but what does it mean to undergo the various stages postulated by the information processing theorist? The advantage of our ordinary terms is that they have definite behavioral implications. When we are told that a person sees something, we know certain things about what s/he is likely to do. This advantage is lost by the information processing analysis. The specific stages have no clear behavioral implications. What goal, then, is served by this program? The answer, it seems to us, is that it allows us to build machines capable of doing what humans do. In other words, a fully successful information processing psychology would, in effect, break our mental phenomena down into sets of elements which a computer could understand. This is extremely valuable, although not what most cognitive psychologists claim to strive for.

What all these atomistic approaches to mind have in common is that they lead to the study of rather exotic forms of human behavior. This, we think, is the ultimate price the psychologist pays for this inap- propriate analogy from the physical sciences. Human activities of intrinsic interest are neglected in favor of other behaviors in the belief that the latter shed particular light on the elements of mind.

Let us now turn to a consideration of the other role physics has played for psychology: as the source of an ontology.

Physics as an ontology

The use of physics as an ontology, as the “given”, is, if anything, even more common than its use as a role model. Virtually all psychologists

[l] Fodor (1980): 65). for example, puts it this way: “Insofar as we think of mental processes as

computational (hence as formal operations defined on representations), it will be natural to take the mind to be, inter alia, a kind of computer.. to a first approximation, we may thus construe

mental operations as pretty directly analogous to those of a Turing machine”.

S. Wilcox, D.A. Edwords / Physics Crttd psychology 151

seem to believe that light, sound, etc., as described by the physicist provide the input to the organism. The task of the psychologist, therefore, becomes the building of models of how this physical input is transformed, added to, etc., in order for the organism to behave appropriately.

Again, we find that the trend goes back to the nineteenth century. Perhaps the most obvious example is Fechner’s psychophysics. In the preface to his Elements of Psychophysics ( 1860/l 966) Fechner described his program thus: “Since the measure of physical magnitudes is already known, the first and main task of this work will be to establish the as yet nonexistent measure of psychic magnitudes”. The modern psycho- physicist might not state the problem exactly the same way, but his science is identical in spirit to Fechner’s. Indeed, the whole area of sensation within psychology relies explicitly upon physics for its description of the stimulus. In effect, sensations are thought to form a mental core of consciousness which corresponds to the physicist’s parameters [2].

Wundt was also explicit in his adoption of the physicist’s description:

We generally understand by stimulus the external motion-process, which, after it has acted upon the sense-organ and been conducted by sensory nerves to the brain, is accompanied by the mental

process of sensation. Thus we regard the sound-waves of the air or the light-waves set up in

surrounding space as stimuli.. (1894: 16).

Even Watson deferred to the physicist for his stimulus description, as is indicated by the following passage.

As examples of stimuli we may name such things as rays of light of different wave lengths; sound

waves differing in amplitude, length, phase, and combination; gaseous particles.. ; solutions

which contain particles of matter.. (1919: 10).

Later in the same work he writes, “Both physiology and psychology are dependent (as is every other science at bottom) upon physics for the

[2] We emphasize in this paper what might be called the “British” reading of the concept of sensation - the view of most of the British Empiricists (including Locke) that sensations are the

result of the direct apprehension of an external physical world. The alternative view which comes out of German philosophy is that sensation (as physics itself) is just one of the modes of mind. Even from this German viewpoint, however, the characteristics of sensations were still similar to

Locke’s primary qualities and, thus, related to classical physics. In any case, it is primarily the British viewpoint which is relevant to “mainsteam” psychology.

control of apparatus and stimulus” ( 1919: 18). A rather surprising modern example of deference to physics is to be

found in the work of Hayek (1952), whose theory of mind is in many ways quite radical. One could not ask for a clearer statement of the position under discussion than the following quote:

Psychology must take the physical world as represented by modern physics as a given and try to reconstruct the process by which the organism classifies the physical events in the manner which is

familiar to us as the order of sensory qualities. In other words: Psychology must start from stimuli

defined in physical terms and proceed to show why and how the senses classify similar physical

stimuli sometimes as alike and sometimes as different and why different physical strmuli will sometimes appear as similar and sometimes as different (Hayek 1952: 7-8).

Even psychologists who do not directly concern themselves with sensation almost always presuppose the physicist’s description as a starting point. As an example, take the following passages from Juola: (1979):

According to the information-processing view, the eyes and ears are input devices or energy transducers. A transducer changes energy of one form (e.g., light) into another (e.g., the electro-

chemical energy of the nervous system). Inputs are recorded by means of operations performed on them in several processing stages in the visual system. In other words. sensory information is

transformed in accordance with the structures and processes of the perceptual system (1979: 494).

Thought and action have two origins: autonomous events internal to the nervous system, and

external surces of information that stimulate peripheral receptors. Data and principles from the

study of sensory physiology and brain function concern how external information enters the

cognitive system. Such data and principles provide boundary conditions for theories about higher

cognitive processes,. Any theory of perception, memory. or longer comprehension must be

partly about what happends to information received by sense organs (I 979: 495).

And as Juola’s statements illustrate, what is considered to be the starting point provides pervasive constraints on the form that any psychological theory takes. Put another way, virtually all psychologists base their models on some view of what is “left over”, that is, unaccounted for by sensations. As Neisser puts it (in regard to perception): “Every account of perception is linked to some particular description of what is available to the eye” (1977: 17). Thus virtually all of the models of mind we find within contemporary psychology follow (directly or indirectly) from the favored ontological status given to the parameters of physics. Light, sound, and mechanical pressure form the components out of which the individual’s reality must be built.

The basic problem with beginning with physics is that the physicist’s description does not contain the furniture of the ordinary person’s

S. Wilcox, D.A. Edwards / Physics and psychology 153

world. Therefore, starting with physics inevitably leads to what Ryle ( 1979) called “duplicationism”, the proposing of additional (and ulti- mately superfluous) explanatory mechanisms. Since we cannot account for what people do by limiting ourselves to the physicist’s language, and since the physicist describes what realZy exists, people must not have direct access to reality. Something must be added somehow to the input and this something decreases the ontological status of the objects of knowledge. The physicist sees reality, but the rest of us are condemned to live in a world of appearance. Thus, the position in which traditional Western (i.e., Cartesian) philosophy found itself was that awe of classical physics engendered skepticism concerning the nature of human knowledge. And if human knowledge is questionable, how can the physicist himself discover what is real? Much of modern philosophy has been an attempt to escape this dilemma [3].

The specific problem for the psychologist caused by beginning with physics is that the physicist’s description does not enhance prediction for psychology, except in very limited realms such as the study of receptor physiology. Even if we successfully analyzed all of the inputs to an organism into their constituents ala physics, where would we be then? Could we predict what people identify as circles, or under what circumstances people become violent? In other words, the traditional Cartesian epistemology which is a consequence of deference to the physicist is particularly problematical, because it precludes the very type of prediction which (in our view at least) must be an integral part of the psychologist’s program, namely, prediction of the effects upon organisms of environmental conditions.

And since the psychologist begins with a description which does not fit his or her needs, s/he is forced into proposing various “internal” causes (e.g., unconscious inferences, schemata) to account for this lack of predictive validity. There are many ironies here. The most obvious is the one we referred to earlier: that it is impossible to see how the physicist himself could ever have achieved access to reality, given that he is a human knower like the rest of us. But besides being stuck with this problematical epistemology, the psychologist is often left in the unenviable position of building models to account for his or her predictive failure. Putting the locus of causation inside the organism, in

[3] See Wilcox and Katz (in press) for a critique of the proposition that a skeptical epistemology

can be achieved by psychological research.

154 S. WI/C-OX, D.A. Edwards ,’ Ph_ysrcs and psychologp

effect, bars the observer from accurate prediction. (For more detailed discussions of this point, see Wilcox and Katz 198 la and b.)

In summary, psychology has traditionally deferred to physics for both the model of what it should be as a discipline and for the description of the “input” to organisms. The question that arises at this juncture is why? Why has psychology relied so heavily upon another discipline?

It is logical that psychology tends to ape physics in view of the latter’s success. However, this does not address the issue of psychology’s deference to physics in the matter of stimulus description. This, it seems to us, is the product of a world view which has had wide acceptance in the West since the success of Newtonian physics. It might be stated as follows. Whereas most of the objects whch the ordinary person has commerce with are “subject-related”, the great achievement of physics is the description of reality in its own terms. To speak of smiles, decisions, university appointments, or even chairs and tables is to implicitly refer to their functions in a human context, but to speak of atoms, photons, etc., is to speak of the absolute or at least the objective nature of the universe. And since the physicist describes the real constituents of physical reality, putting the stimulus in his hands is less a matter of choice than a matter of necessity. Indeed, the feeling seems to be that except in its naive, commonsense use, physical refers to the physicist’s description.

For example, in arguing for the futility of what he calls a “naturalis- tic psychology”. (i.e., a psychology which contains environment as a basic component), Fodor tells us

the requirement that the stimulus be physically specified has been ignored by just about all

practitioners. And, indeed, they were well advised to ignore it. how else could they get on with

their job? If they really had to wait for the physicist to determine the description(s) under which

pencils are law-instantiators, how would the psychology of pencils get off the ground? (1980: 71).

Taylor (1980: 31-32) states this view of physics explicitly:

An account of things which eschews.. subject-related descriptions can be called an absolute account. And it has seemed a sound principle of scientific explanation since the seventeenth century that the world should be accounted for in absolute terms. For after all, it exists

independently of us human percipients, and hence must be understood in terms which reflect this.

In the next two sections we attempt to dismantle this absolutist view of the physical sciences. First we will present the philosophical case

S. Wilcox, D.A. Edwards / Physm and psychology 155

against using physics for one’s ontology; then we will show that in any case physics, itself, does not speak with one voice.

Physics as a problematic ontology

Locke built Newton’s physics into his ontology and was, therefore, forced into making the so-called primary-secondary distinction. The rejection of Locke’s distinction between primary qualities (which are “in the world” and akin to Newton’s basic elements) and secondary qualities (which are only in the minds of knowers) is one thing which most phenomenologists, linguistic analysts, and American pragmatists have in common. As Edwin Burtt put it:

The developments [e.g., in biology] strongly suggest that reality can only be consistently regarded

as a more complex affair, that the primary qualities simply characterize nature so far as she is

subject to mathematical handling, while she just as really harbors the secondary and tertiary ones

so far as she is a medley of orderly but irreducible qualities (1924: 304).

Rorty (1980) has recently discussed this issue. The following passages are references to Taylor’s claim quoted earlier that physics describes reality in absolute terms.

Taylor thinks that seventeenth-century science was on firm ground in demanding that “the world be accounted for in absolute terms”. I think that this demand embodies a confusion between the

pragmatic success of mechanistic explanation and the incoherent philosophical demand to know

things as they are apart from knowledge (1980: 40).

I do not think we have any idea of what it would be like to “account for the world in absolute

terms”. We can only make sense of accounting for it in terms useful or this or that human purpose,

but we cannot make sense of describing it “in its own terms” (1980: 40).

When nature was believed to be planned by God, or when nature itself was personalized.. it made some sense to think that bits of our vocabulary were more “natural” than others.. But once God

is lost and nature mechanized, the suggestion that there is a “natural” or “absolute” vocabulary makes no sense. _. To say with “scientific realists” that because we have hit upon one method of

predicting and controlling nature we have hit upon a way of describing nature in “absolute terms” _ in its own terms - is just paying ourselves a pointless epistemological compliment (1980: 42-43).

The idea, then, is that the notion of an absolute reality - which we can describe as it is apart from human knowledge - is a contradiction in terms. To describe anything is to describe it from our point of view. And, if this is so, physics is on the same ontological footing as

156 S. Wilcox, D.A. Edwards / Physics and psychology

everything else - as a description of the world from a particular point of view, or, rather, as the next section will show, from particular points of view.

Three theories of light

In this section we describe three different approaches to the physics of light. We have chosen to discuss light as an examplar because theories of light have traditionally been important for psychology. For purposes of comparison, we will focus upon a hypothetical observer looking at the sun.

1. The classical view: local realism

The theory of light to which Descartes subscribed (and which Newton preferred although he could not figure out a mechanism for it) did not contain action at a distance either through space or through time. Interactions were only local - akin to mechanical waves in elastic media. For our observer of the sun, the sun would be described as emitting light which travels along a definite path, and after a period of time reaches the oberver’s retina. The light then stimulates the retina by causing chemical transformations which set up nerve impulses which allow perceptions to take place.

Thus, from this traditional point of view, the input to the eye is of a local nature. Therefore, as we have seen, local detection must be coupled with some sort of leap or inference to allow the perception of distant objects; hence we have a distinction between the “proximal” and the “distal” stimulus. Even Gibson’s notion of the “ambient optic array” is not free of these traditional assumptions. The ambient optic array is different from the traditional “retinal image” notion of the proximal stimulus in that the former but not the latter is thought to be specific to that which it specifies. By taking into account higher-order structure of both a spatial and a temporal nature, Gibson has successfully shown how patterns of light can unambiguously specify properties of the environment. Thus, Gibson’s view is a direct theory of perception in the sense that there is nothing left for the mind to disambiguate.

However, there is still another sense in which perception is not direct for Gibson. In Gibson’s view the ambient array contains information

S. Wilcox, D.A. Edwards / Physics and psycholog) 157

which specifies the environment. This information must be “picked up”. But there is a problem here. How does the organism know what characteristics of the ambient array correspond to what characteristics of the environment? This is the problem of “translation” or “coding” which has been mentioned by authors who are otherwise sympathetic to Gibson (e.g., Johannson 1970; Mace 1977). This “picking up” of information seems dangerously close to being an unconscious mental activity - a category of existants which Gibson’s approach is designed to do away with [4].

The way to avoid this danger, we think, is to interpret the ambient array as being a part of the scientist’s world, not of the perceiver’s. The typical perceiver sees surfaces, objects, etc. The scientist observes the perceiver and, using various instruments, sees things in a different way. Then the scientist correlates what he sees vis-a-vis the ambient array with what the perceiver sees. The claim that the ordinary perceiver sees the ambient array is patently false, and the claim that the perceiver picks up information from the ambient array comes awfully close to this. (We will have more to say about this below.)

But so long as one’s theory of light is a local theory, the ambient array must be conceived of as a part of the ordinary perceiver’s world as well as the scientist’s. Therefore, let us turn to a theory of light which does not require the localist assumptions.

2. Action at a distance: the Feynman- Wheeler theory

Although Newton grudgingly accepted action at a distance through space, the classical view did not allow action at a distance through time. For every effect there had to be an immediately preceeding cause. On the other hand, the Feynman-Wheeler approach (see Feynman 1972) contains the concept of action at a distance through both time and space. The basic elements are electrons, which can interact in some very interesting ways. For example, the activity of a given electron can be directly affected by the activity of another electron which is distant in space and either in the past or even the future of the first electron.

[4] We do not mean to imply that Gibson thought of the ambient array as a mediator between the environment and the organism’s perception. He explicitly denied this interpretation. However, it is

not completely clear from Gibson’s writings what this “pick up” was supposed to entail. The construal of the ambient array which we offer here is the only way that we can see of eliminating

the tendency to think of the ambient array in this “mediational” way.

To return to our observer of the sun, the correct description from the Feynman-Wheeler point of view would be something like the following. There is activity of electrons on the sun which directly affects the activity (some minutes later in time) of other electrons on the observer’s retina. There is no path of light through space and time. In fact, light is not even a primitive component of the Feynman-Wheeler theory. What we call light would be conceived of as an epiphenomenon of interactions between groups of electrons.

Although only 2-body intractions are an explicit part of the theory, an extension to N-body interactions would yield a type of direct realism. Retinal stimulation could be thought of as the direct result of properties of the “distal” stimulus. in this sense, the optic array would not be a part of the observer’s world at all. It would be described along the following lines. The scientist has measuring devices containing electrons which can be affected by the activity of the sun’s electrons. The optic array would be a map of the locations in space and time from whch the sun could be detected by the device, i.e., those locations in which the device’s electrons are affected by the sun’s electrons. The problem then would be to make predictions about the observer’s perceptions based upon this derived map (i.e., optic array). There would be no reason to assume that the observer contained within himself a measuring device like the scientist’s. Therefore, the optic array would not be something the observer has to contend with at all. It would truly not be a part of his world.

Although the Feynman-Wheeler theory is very different from Newto- nian physics, it is still a “classical” theory in the sense that the fundamental mechanism is the interaction of electrons. The point of view of the observer is not explicitly brought into the theory as it is in quantum mechanics, which we discuss in the following section.

3. Modern quantum mechanics

The grammar of classical physics consists of fundamental sentences of the form: property A has value a. Any appeal to probability is considered a weakness. According to the standard interpretation of quantum mechanics, however, the fundamental sentences read: if you look in mode A you will see a with probability p. The use of probability here is not viewed as a weakness but instead as the “bottom line”. Further- more, not all modes of perception are assumed to be compatible. Using

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some modes excludes others. One, therefore, assumes the existence of interlocking modes of perception together with a probability assign- ment. (See Edwards 1979, for a detailed presentation of the foundations of quantum mechanics.)

Thus, the technical terms of quantum mechanics such as electron and photon refer to the results of probabilistic samplings, not to classical objects which can be said to exist whether or not someone is looking. What does exist when one is not looking is a stochastic disposition, not an electron or photon. It follows that it makes no sense to describe objects as being made up of electrons or even light as being made up of photons. To see objects or to see light is to adopt a different mode of perception from the one which yields electrons of photons.

For our observer looking at the sun, we can say that if he looks in a particular way, he will see a particular thing, namely, the sun. If the physicist applied a photon detector to that same region of space-time he would obtain a particular result with a particular probability. The optic array would be generated as with the Feynman-Wheeler theory, as a mapping of readings from a measuring device, but there would be no talk of interactions between electrons. The ambient array would be a description of the expected results of applying photon detectors to the relevant region of space-time. It would make even less sense (as compared to the Feynman-Wheeler theory) from the point of view of quantum mechanics to consider the optic array to be part of the observer’s experience. The optic array is only a part of one’s experience if one has a photon detector, or more properly, an ensemble of photon detectors.

In summary, even something as seemingly straightforward as light can be described in different ways depending upon the particular physics one adopts, so even the psychologist who insists upon deferring to the physicist for the “input” is left with a choice of several approaches to physics, each of which would lead to a different psychology. In practice the psychologist has relied upon classical physics. Our point, though, is not that the psychologist should rely instead upon some more modern physics, but rather that s/he has no need to rely upon physics at all. The existence of several approaches to physics does not seem compatible with the absolutist view of physics which, in our opinion, underlies the typical psychologist’s theory of knowledge.

Conclusion

We have argued that physics, rather than having favored access to reality, merely offers us one way of looking at reality, one which has proven extremely successful for certain types of prediction and control. If our arguments are correct, it follows that the psychologist is free, and in fact obligated, to develop his or her own description of the physical world, one which suits his or her particular needs. But what are these needs? If the psychologist’s theory of environment is not provided by physics, from what should such a theory be derived? Our answer, as we have already intimated, is that a theory of environment (i.e., a theory of the physical) should be based upon direct realism which might be stated as the principle that “the objects of experience are properties of the world”. It follows from this that the psychologist should, in effect, begin with experience and fit a physical description to it, rather than begin with a physical description and try to fit experience to it [5]. A person’s environment (to treat the human case), then, is that particular collection of properties which s/he experiences. The other side of the coin is the functionalist precept that “experience is the handmaiden of action”. Adding this to our initial formulation of direct realism leads to the principle that “the objects of experience are those properties of the world which are relevant to the actions (i.e., purposes, goals) of the experience?. One way of thinking of this “ecological” viewpoint is that it sees environment, experience, and action as isomorphic to each other. That is, for any given property of environment, there is a corresponding action or set of actions upon it, and an experience of it. Or looked at in another way, any experience has an environmental object and a set of behavioral implications. Likewise, any action has an environmental object which is experienced [6].

[5] The reader should not infer from this that any sort of idealism is implied. The hallmark of idealism is that a causal relation is proposed between the knower and the known, i.e., the objects of

experience are thought to depend for their existence upon the experiencer. We reject any such claim. On the other hand, we do think of the objects of experience as having an eprstemic relation

to the experiencer (cf. Rorty 1980). That is, that which is experienced is experienced from a

particular point of view. It goes without saying that there can always be other points of view. We might say that the world goes on about its business independent of observers (qua observers) but

an animal’s environment is that particular collection of properties which it experiences, i.e., which are relevant to its purposes. [6] See Shaw et al. (1982) for a much more thorough (and somewhat different) formulation of

direct realism.

S. Wilcox, D.A. Edwcrrds / Physics and psychology 161

Out of this context comes Gibson’s notion of an “ecological physics”. In his book The ecological approach to visual perception, Gibson lays out a theory of environment designed to be commensurate with the activities (and experiences) of animals. It consists of surfaces, substances, and a medium which change through time (thus generating events). He contrasts this with the world of physics:

The world of physics encompasses everything from atoms through terrestrial objects to galaxies. These things exist at different levels of size that go to almost unimaginable extremes. __. The

size-level at which the environment exists is the intermediate one that is measured in millimeters

and meters. The ordinary familiar things of the earth are of this size.. In short, the sizes and

masses of things in the environment are comparable with those of the animals (1979: 8-9).

We are concerned here with things at the ecological level, with the habitat of animals and men,

because we all behave with respect to things we can look at and feel, or smell and taste, and events

we can listen to. The sense organs of animals, the perceptual system.. are not capable of detecting

atoms or galaxies (1979: 9).

Since this “ecological level” is designed to be a description of the objects of direct experience, Gibson avoids any sort of primary-secondary or mental-physical dualism. In doing so Gibson has rejected the notion that “sensation” is the basis of perception. Animals do not directly apprehend the meaningless elements of physics and then “process” then or “infer” from them to a meaningful world. Rather, they directly perceive a meaningful environment, or what he has also called a “affordance structure”. As he puts it, “The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill” (1979: 127).

We might say, for example, that a person chose a particular path, or felt fear, or stopped suddenly or saw a brink because his or her environment contained a brink. The psychologists’ task is to find the brink, so to speak - to develop an environmental description which contains brinks which are treated as such by the animal/person in question; and which can be consistently identified (and hopefully manipulated) by the psychologist.

Thus, Gibson’s ecological approach to psychology is a psychology informed by direct realism - a psychology which takes the isomorphism between environment, experience, and action as its starting point. For the ecological psychologist, action and experience are to be understood in terms of their place in an animal-environment system, rather than analyzed into their sub-components. There is no place for a “mecha-

162 S. W~lcou, D.A. Edwards / Ph_vsics and psycho&

nism” inside the organism whch disambiguates the input, because the input is not considered to be ambiguous. Prima facie evidence for ambiguous input to an organism would always be taken by the Gibso- nian as evidence that the environment had not been properly described by the scientist.

The place of physiological mechanisms within this ecological frame- work, is similar to that of the ambient array. Both must be seen as the means by whch an organism comes into direct contact with the environment. As materialists we take it as a given that any experience is made possible by some state of the nervous system. These physiological mechanisms are the objects of the scientists experience, however, not the person’s. We must not, for example, think of people as seeing their retinae, any more than we should think of them as seeing the ambient array. Again, priority must be given to the direct relationship between an animal and its environment. Physiological models which do not reflect this relationship will be reevaluated by the Gibsonian, and, in general, physiology will not be allowed to “drive” theories of knowledge.

In summary, Gibson makes it possible to avoid the Cartesian epistemology which leads to a self-defeating skepticism (and a rejection of the possibility of psychological prediction) by starting with an alternative description of the physical world. We have argued in defense of Gibson that an absolutist account of physics is not tenable; therefore, there is no logical reason why there cannot be other physical descriptions besides those of physics. Indeed we would expect different physical descriptions, since there are many different purposes to which descriptions might be put. This, in effect, brings us full circle. We can say that the world of physics is one particular affordance structure, certainly a very powerful one, but just one particular affordance structure, nonetheless. Thus, the physicist’s elements, although meaningless to the ordinary person, are far from meaningless to the physicist.

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Some Gibsonian perspectives on the ways that psychologists use physics

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