art and the mind || pictorial functions in perception

National Art Education Association

Pictorial Functions in PerceptionAuthor(s): Julian HochbergSource: Art Education, Vol. 36, No. 2, Art and the Mind (Mar., 1983), pp. 15-18Published by: National Art Education AssociationStable URL: http://www.jstor.org/stable/3192655 .

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Pictorial Functions in Perception

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Julian Hochberg

P hilosophers and psychologists have been concerned for their own reasons with pictorial art,

and particularly with the notions of representation and realism and what these might mean. By and large, I don't think that either the philosophy or the psychology have been particularly careful or self-critical efforts, perhaps because they are not subjected to the harrowing scrutiny that can be expected from a fully informed and combative group of peers. This does not do much damage to either discipline because these questions have not been central to either. But some of the writings in question are taken up by artists and art theorists and art educators, and then used as the academic bedrock upon which some stylis- tic or pedagogic edifice is justified.

When that happens, there is danger of unseemly cacaphony in the attempt to justify the financial status of one set of canvas collectibles as against another. And there is danger that some cur- riculum will be advanced on the basis of scientific support where there is only amateur speculation by some interested philosopher or psychologist.

Even those prospects can be viewed with some equanimity, but the relationship between artistic representation and the scientific study of perception is about to move into high technology and big business (and even into the military- industrial complex). Pictures are no longer being made only by human artists nor selected only by human editors, gallery owners, or teachers; interactive computer graphics are now producing pictures that are intended to represent things and events to humans in a com- prehensive, effective, and interesting fashion, and, in many functions, com- puters generate the pictures and show them to human viewers without any other human ever having seen them. This means that we have to understand what effective representations are, well enough to be able to instruct machines as to how to make them. Unlike the use of verbal and digital information, in which the user can accommodate to the convenience of the computer and its

programmer, pictorial material for its nature and unique value depends on the nature of the viewer's perceptual system.

And here is where the lessons that are taken from the discussions of philosophers and psychologists are often quite misleading (not to say downright wrong). The problem for the philosopher arises because, in many ways, a picture is totally different from its subject. let us briefly review why that is true, starting with the picture that is in fact most like its subject - the trompe l'oeil painted according to the prescription of Leonardo's window.

The pictures with which perception psychologists have tended to be most comfortable are those that are intended to send the same light to the eye as does the scene itself - surrogates for the scene. These are not merely inventions of the psychologist. Before photogra- phy, the camera obscura, masters' note- books, and the study of perspective provided a discipline that would teach the artist the set of devices needed to provide a surrogate of any scene - the patterns, or "depth cues," that are charac- teristic of the flat projections of natural scenes in three-dimensional space.

To the extent that such efforts are suc- cessful - fully "illusionistic" - they should be no more interesting to a psychologist or to a philosopher than is a mirror: A perfect surrogate which offers the same light as the scene itself is the scene, visually speaking, and provides no problems that are not already posed by any attempt to explain the scene itself. But such fidelity could at best be achieved, as Leonardo knew, only in the case of a stationary, monocular observer, positioned at just that point in space that provides the same array of light as would the depicted scene. These conditions are rarely even approxi- mated.

The fact is that virtually all pictures depart from such perfect fidelity, and that makes them very different, in what would seem to be a fundamental way, from either a mirror or the scene itself. Viewers move, and even a slight movement can serve to disclose the fact that the picture is not a parallel road receding into distance, but is a set of lines converging on a flat dappled board. Or, if

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viewers did for some reason see the scene and not merely the pigmented canvas, the notion that a picture is a surrogate should lead us to expect that the scene being depicted must itself change with every change in viewpoint. (Some signs of this can in fact be shown (Gold- stein, 1976), but the phenomenon is not an important factor in pictorial representation.) And even discounting the questions introduced by viewer motion, pictures simply do not in general send the same light to the eye as scenes they represent, for reasons we consider next.

Pigment on a canvas, or ink on a printed surface, is normally seen for what it is. (There are of course devices, like hiding the brush strokes, and gen- erous sfumato, that can minimize the salience of this fact - cf. Hochberg, 1979, 1980 - but does not eliminate it.) And indeed, for what must still be the overwhelming majority of pictures, what the viewer faces is line drawings, ribbons of pigment on flat paper which are routinely used to represent objects' edges, the horizons of curved surfaces, modeling of form in light and shade, etc. (Hochberg, 1962, 1980).) Most pictures, in short, depart from fidelity not only because of such inadvertence as viewer movement or pigment visibility, but by choice of medium and, indeed, by the way in which the medium is used. That is, as every art historian knows - and as practically every perception psychologist who writes about the visual arts resolutely ignores - artists routinely take deliberate steps to destroy the fidelity of their pictures. Indeed, even before the Gestalt laws were formulated, painters since Cezanne and Vuillard have deliberately used the same princi- ples to make their canvases look flat; indeed, Matisse's Blue Window is a manual of the "law of good continua- tion," used to defeat any vestige of il- lusionism and to make sure that the viewer sees the pattern of pigment for what it is (Hochberg, 1980).

We can now see why the philosopher rightly considered that pictures are radically different from the scene they represent. How is it then that the picture and the scene can elicit the same response?

Given the evident differences we have discussed, it has been argued by both philosophers and psychologists that we must learn to see pictures. Let us consider both the argument, and the reality.

Among philosophers, Goodman (1968) and Wartofsky (1979) are the most notable proponents of this position, in this camp. For example, Good- man says that (almost) any picture can be used to represent (almost) any thing. We will see that this is (almost) totally false. The implication of this position is that pictures work as they do because of pictorial conventions that were invented by the artist or by society, and that are selected and sustained by society and culture. This consequence of the War- tofsky/Goodman positions is also main- tained by art theorists (such as Kepes and by Gombrich - sometimes, but not always) - i.e., that there is a "language of vision" or a "language of pictorial art" that must be learned as other language is learned.

This position has also been taken by psychologists, for similar reasons. To J.J. Gibson (1966, 1979), as to others, "natural" perception is perception by a moving viewer; that perception is a ver- idical and "direct" response to the information in the light at the eye. It follows rigorously from this position, I believe, that viewers should not see the scene, but only the pigmented canvas, and the pattern which is perceived on that canvas should bear no relationship to the perceived disposition of things in the world. That is, there is no similarity between the converging lines on the drawing of the road, and the parallel surface of the road itself stretching off to the horizon.

Pictures thus represented a serious challenge to Gibson's broader theory, and initially he confronted them much as Goodman did (although he never actually agreed with Goodman's assertion that they were arbitrary, inasmuch as he retained surrogates as a model for pictures). In the case of lines drawings, the similarity to Goodman is immediate in Gibson's earlier writings: Gibson argued that because line drawings are so fun- damentally different from the edges of the objects that they represent, these pictorial devices must be specificially learned (1951). He later waffled on this, and Kennedy (1974) has even claimed that Gibson pioneered the opposite view, but the fact is that Gibson's approach demanded and demands the con- clusion that line drawings are a learned visual language.

No matter how well reasoned, these arguments are invalid. The fact is other- wise: Pictures (even outline drawings)

can be recognized on the viewer's first contact with them, even if that viewer has had no prior training whatsoever in pairing pictures with their objects (Hochberg and Brooks, 1962).1

We can therefore reject the first ex- planation of why we respond in the same ways to scenes and to their pictures, even though the latter are so very different from the former. If the ability to perceive pictures is learned at all, it is learned simply by commerce with the world, and not as the result of a paired- associates process like learning a language in school. That means that flat pictures must share some features with the three-dimensional world they represent. That is, the pictorial depth cues must also be presented to us by real scenes, or we would not be able to use them when they are given us by pictures.

No philosopher has, to my knowledge, addressed this question at all. Gib- son did at one time try to formulate a way in which pictures and scenes might share the same invariant information (1971), but never really did so in a man- ner that differed from a restatement of the depth cues, and finally appeared to have relinquished the attempt (1979). His students have apparently not yet noticed that retreat. Some very nice work (e.g., Sedgwick, 1981) explicating the pictorial depth cues continues to be done by people who think of themselves as being within Gibson's framework. The very fact that pictures work without special learning, however, is not com- patible with Gibson's general position: It necessarily implies that the full scene as viewed by the free observer must share something with the static flat surface. There is simply nothing on the canvas, as a flat layout of pigment, that cor- responds in any way with the layout of surfaces in the scene. Inasmuch as these are the invariants in the Gibsonian theoretical system, there is in fact no evident way in which the theory can deal with the facts.

We must re-examine with some care what we actually know about the fine structure of the perceptual process, as it applies to pictures and to the world. In fact, if we actually examine in con- crete terms the sensory and perceptual processes involved in looking at pictures, and in looking at the world, it turns out that they share a great deal: The sensory information that indicates that a particular contour is a pigment outline and not an object's edge, is far


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more available to the fovea (a tiny region in the center of the eye) than to the much greater peripheral retina (Hochberg, 1979, 1980). The pictorial depth cues, however, are quite visible in the periphery. Although pictures and their scenes are indeed very different as physical objects, those differences are detectible only within a small region within each individual glance because of the limitations of our visual apparatus. If we elect to move our eyes to places that will reveal that the array before us is a flat picture and not a three- dimensional scene, of course we con- front a pigmented canvas; but if we do not elect to move our eyes to perform those tests, and especially avoid looking at the depicted edges of objects, the information from picture and from scene are very much the same (Hochberg, 1980), and produce the same perceptual impression.

But what about head movements? Don't they immediately make picture and object very different optically? The answer is that they can, but they need not. First, we should note that the information from motion parallax that could inform the viewer that the paint- ing is flat and not a layout of surfaces in depth is also poorly picked up, out- side of the small fovea (Hochberg, Green and Virsotek, 1978). To the pre- ponderance-of vision at any moment peripheral vision - the differences between picture and scene are indetectible. Second, it is surely a gross exaggeration to say that "natural" perception requires a moving perceiver: Both people and animals spend some nontrivial part of their perceptual lives in not moving while they look at things.2 Indeed, there are surely perceptual functions that require the viewer to avoid parallax, and even to attend the world as though it were a flat array: Although perception of the third dimension is essential for many actions, there are others to which the perception of the relationships within the two-dimensional visual field is important - the guidance of eye movements, the guidance of a head movement that is to disocclude some object that appears to be concealed by another object, the aiming of a gun. The "un- naturalness" of this general ability to perceive the visual field, to which picture and scene are the same, has been exaggerated to a degree that we cannot presently estimate.

In the momentary glance, therefore,

picture and scene are not all that different. What happens when we take our subsequent glances?

The details that can be discerned in foveal vision in one glance are usually no longer visible in the next. They must nevertheless be taken into account in deciding where to glance next, in putting together the successive fragments of information, and in terminating the elec- tive perceptual inquiry when the viewer's schema is sufficiently filled out for the purpose of the task that he or she is pur- suing. If the pattern is random or mean- ingless, the viewer has no expectations to text, nor any structure by which to remember what the sequence of glimpses contained.

Now, the patterns of a picture as such are (except to the trained artist) not a meaningful structure: The painted object is merely an unmemorable dappled pattern of pigment. That is, the dappled surface pattern as such provides no guidance to my perceptuomotor expectations - what will I see if I look at that blob over there? or what change should I expect if I move my head to the left? - nor will it in general correspond to any available schema for storing what has been seen (unless there are symme- tries or other redundancies which make the canvas a "decorative," memorable object in its own right): Only if the viewer treats the flat pattern as though it were a scene in depth, will the normal schemas, acquired in the course of deal- ing with the world, provide meaning to the sequence of successive glances at the picture.

What allows pictures to represent objects and layouts in the world, then, is that we can fit schemas we have learned from the world, to the patterns that are presented to the eye by the pictures themselves.

This is why a picture need not appear to be at all three-dimensional itself in order to represent a three-dimensional object or scene. If it is to be a picture at all, however, it absolutely must allow the viewer to realize that it is a picture, and must enable him or her to execute specific perceptual tests - to look at this place or at that one - and to receive visual answers that would have been ap- propriate if the viewer were looking at the represented scene or object.

Note too that because pictures and their scenes are not merely in an arbitrary relation, it is potentially meaningful to talk about varying degrees and kinds of "realism." In the El Greco, the folds and modeling permit me to apply my local schemas of surface texture, but my schemas as to where the parts of the body are to be found must be greatly .transformed to fit the unrealistic elon- gation. In the Diebenkorn drawing before me, I can recognize that the ar- rangements of lines on paper fit with high precision my construction of where the horizons of the limbs of a seated female body will lie, but between those lines themselves there stretches only the slightly textured surface of the white paper, unapologetically unrealistic in its lack of the modeling and highlights that would meet my gaze were I looking at the woman herself.

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We simply cannot talk about pictures, then, nor about the pictorial function, without talking as well about the schemas to which they can be fitted. Merely recognizing that fact does not advance our effective knowledge very much, however, because we really do not know much about the schemas that are employed in serving the pictorial function. Schemas are not copies of the physical world - they are mental devices, with properties that we can as yet explicate in only the most rudimen- tary way, for guiding our perceptual in- quiries and storing our visual findings.

If the properties of schemas were indeed those of the objects and events in the world, we could by knowing the latter specify how well some schema would fit some picture, and know, too, how ef- fectively any picture would serve its pictorial functions. We know that schemas do not obey the constraints of the physical world. If the perception psychologist did not already know that outlines could represent objects, he or she would never have predicted that they would. The famous impossible objects of Pen- rose and Penrose, and Escher's even more famous adaptations of them, teach us that the fact that you perceive a different orientation when looking at the left and the right corners of a single object does not cause any perceptual crisis - i.e., that the schema which bridges the successive glances is indifferent to such physical aspects (Hochberg, 1968; 1980). And these unexpected characteristics of our schemas about object rigid- ity and connectedness would never have been suspected had Penrose and Penrose not discovered them as such. We do not know what other properties pictorial schemas have or lack. They have really not been studied.

These considerations show how un- informative it is to ascribe the characteristics of picture-perception to those of the physical world. But to ascribe them to "culture" or "convention" is even more vacuous: If the immense over- learning that is provided by our exposure to the constraints of physics does not suffice to specify the characteristics of our perceptual schemas of physical relationship, the relatively lighter im- prints of cultural exposure should do no better. The detailed experimental study of perceptual schemas is needed if our understanding of picture perception is to be predictive and not merely descrip- tive or explanatory.

That brings me back to the point I raised near the beginning of this paper. Why should we feel it necessary to understand picture perception with such rigor? After all, the experienced artist, with a tentative stroke of the pencil, or the photographer with a preliminary look in the view finder, can immediately discern that the picture before him or her is a bad one. And if the incompre- hensible or ineffectual picture should reach the editor or the gallery owner, it can be discarded at that stage (or perhaps justified by appeal to some new esthetic.) Throughout our pictorial history, we have been heavily screened from the misleading, the cluttered, the too-demanding representation.

That is no longer the case. We are now in the position of having to instruct the totally new intelligence that has joined us in the universe - the computer - in the conception, execution, and presentation of pictures. This is no longer a matter of fanciful exercise, but economic and technical necessity. In order to be able to do that, we must find out much more about ourselves. I can't imagine anything that is likely to prove healthier for our understanding of the perceptual processes that make possible the pictorial functions.

Julian Hochberg is Centennial Profes- sor of Psychology at Columbia Univer- sity, New York, New York.

References

Gibson, J. J., "What is a Form?" Psycho- logical Review, 1951, Vol. 58, pp. 403-412.

Gibson, J. J., "The Information Available in Pictures," Leonardo, 1971, Vol. 4, pp. 27-35.

Gibson, J. J., The Senses Considered as Perceptual Systems, Boston: Houghton Mifflin, 1950.

Gibson, J. J., The Ecological Approach to Visual Perception, Boston: Houghton Mifflin, 1979.

Goldstein, E. B., "The Rotation of Objects in Pictures Viewed at an Angle: Evidence for Two Types of Pictorial Space," Journal of Experimental Psychology: Human Perception and Performance, 1976, Vol. 2, pp. 130-138.

Goodman, N., Languages of Art: An Ap- proach to a Theory of Symbols, In- dianapolis: Bobbs-Merrill, 1968.

Hochberg, J., "The Psychophysics of Pic- torial Perception," Audio-Visual Com-

munication Review, 1962, Vol. 10, pp. 22-54.

Hochberg, J., "Some of the Things That Pictures Are," in C. Nodine and D. Fisher, eds., Views of Pictorial Repre- sentation: Making, Perceiving, and In- terpreting, New York: Praeger, 1979.

Hochberg, J., "Pictorial Functions and Per- ceptual Structures," in M. Hagen, ed., The Perception of Pictures,Vol. 2. New York: Academic Press, 1980.

Hochberg, J., and Brooks, V., "Pictorial Recognition as an Unlearned Ability: A Study of One Child's Performance," American Journal oJ'Psychology, 1962, Vol. 75, pp. 624-628.

Hochberg, J., Green, J., and Virostek, S., "Texture Occlusion Requires Central Viewing: Demonstrations, Data and Theoretical Implications," Unpublished paper read at American Psychological Association Convention, Toronto, 1978. Ms. Available from first author.

Kennedy, J. M., A Psychology of Picture Perception, San Francisco: Jossey-Bass, 1974.

Sedgwick, H. A., "The Geometry of Spatial Layout in Pictorial Representation," in M. Hagen, ed., The Perception of Pic- tures, Vol. 1, New York: Academic Press, 1980.

Wartofsky, M., "Picturing and Represent- ing," in C. Nodine and D. Fisher, eds., Views of Pictorial Representation: Mak- ing, Perceiving and Interpreting, New York: Praeger, 1979.

Footnotes

'I have occasion to say something like this to art educators or art theorists, from time to time, and I am almost always meet with something like "But Goodman (or War- tofsky) says. . ." The fact is that these data have been well known for at least two decades. (And anyone with grandparents who had grown up in a religion that forbade all representational pictures knew the truth before the research was done.) But that does not seem to deter the theorists who regard pictures as merely another kind of symbolic, acquired language (cf. Wartofsky, 1981).

2Out of doors, I observe myself and others (and their cats and dogs as well) to "freeze" quite frequently, as when staring at some bush that has emitted a suspicious sound; indoors, we often sit with immobile head (e.g., on hand or paws), using only eye movements to observe the scene. One might argue that binocular parallax then takes the place of motion parallax. That source of information, however, is also subject to the fovea-periphery difference; is often hindered by occlusion; and fails to provide information about the depth at distant edges, and about the disposition of smooth surfaces at near distances if the gaze is kept away from their edges (Hochberg, 1980).


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