James J. Gibson (1979) The Ecological Approach to Visual Perception. New Jersey, Lawrence Erlbaum Associates, Publishers

Chapter 4 The Relationship Between Stimulation and Stimulus Information

For visual perception, the information is obviously in light. But the term light means different things in different sciences, and we shall have to sort out the different meanings to avoid confusion. Most of us are confused, including the scientists themselves. The science of light is called optics.

What I call ecological optics is concerned with the available information for perception and differs from physical optics, from geometrical optics, and also from physiological optics. Ecological optics cuts across the boundaries of these existing disciplines, borrowing from all but going beyond them.

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The eye-head-brain-body system registers the invariants in the structure of the ambient light. The eye is not a camera that forms and delivers an image, nor is the retina simply a keyboard that can be struck by fingers of light.

A Demonstration That The Retinal Image Is Not Necessary For Vision

The camera eye has a concave mosaic of photoreceptors, a retina. The compound eye has a convex packet of photoreceptive light tubes. The former accepts an infinite number of pencils of light, each focused to a point and combining to make a continuous image.

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We also communicate with others by making a picture on a surface (clay tablet, papyrus, paper, wall, canvas or screen) and by making a sculpture, a model, or a solid image. In the history of image-making, the chief technological revolution was brought about by the invention of photography, that is, of a photosensitive surface that could be placed at the back of a darkened chamber with a lens in front. This kind of communication, which we call graphic or plastic, does not consist of signs or signals and is not so obviously a message from one person to another. It is not so obviously transmitted or conveyed. Pictures and sculptures are apt to be displayed, and thus they contain information and make it available to anyone who looks. They nevertheless are, like the spoken and written words of language, man-made. They provide information that, like the information conveyed by words, is mediated by the perception of the first observer. They doe not permit firsthand experience – only experience at second hand.

Definition of what ‘picture’ means

We cannot convey information about the world to others unless we have perceived the world. And the available information for our perception is radically different from the information we convey.

Link this to Hockneys quote on seeing through your own consciousness

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The information that can be extracted from ambient light is not the kind of information that is transmitted over a channel. There is no sender outside the head and no receiver inside the head.

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The Laws of Natural Perspective: The Intercept Angle

The notion of a visual angle with its apex at the eye and its base at an object in the world is very old. It goes back to Euclid who postulated what he called a “visual cone” for each object in space. The term is not exact, for the object need not be circular and the figure does not have to be a cone. Ptolemy spoke of the “visual pyramid,” which implied that the object was rectangular. Actually, we should refer to the face of an object, which can have any shape whatever, and to a corresponding solid angle, having an envelope. A cross-section of this envelope is what we call the outline of the object. We can now note that the solid angle shrinks as the distance of the object from the apex increases, and it is literally squeezed as the face of the object is slanted of turned. These are the two main laws of perspective for objects. Euclid and Ptolemy and their successors for many centuries never doubted that objects were seen by means of these solid angles, whether conical, pyramidal, or otherwise. They were the basis of ancient optics. Nothing was then known of inverted retinal images, and the comparison of the eye with a camera would not be made for a thousand years. The ancients did not understand the eye, they were puzzled by light, they had no conception of the modern doctrine that nothing gets into the eye but light, but they were clear about visual angles.

Natural perspective does not apply to shadows with penumbras and patches of light. It does not apply to sunlit surfaces with varying degrees of illumination. It geometrizes the environment and thus oversimplifies it. The most serious limitation, however, is that natural perspective omits motion from its consideration. The ambient optic array is treated as if its structure were frozen in time and as if the point of observation were motionless.

Although I have called the discipline natural perspective, the ancients called it perspectiva, the Latin word for what we now call optics. In modern times, the term perspective has come to mean a technique – the technique of picture-making. A picture is a surface, whether it be painted by hand or processed by photography, and perspective is the art of “representing” the geometrical relationships of natural objects on that surface. When the Renaissance painters discovered the procedures for perspective representation, they very properly called the method artificial perspective. They understood that this had to be distinguished from the natural perspective that governed the ordinary perception of the environment. Since that time we have become so picture-minded, so dominated by pictorial thinking, that we have ceased to make the distinction. But to confuse pictorial perspective with natural perspective is to misconceive the problem of visual perception at the outset. The so-called cues for depth in a picture are not at all the same as the information for surface layout in a frozen ambient array, although pictorial thinking about perception tempts us to assume that they are the same. Pictures are artificial displays of information frozen in time, and this fact will be evident when the special kind of visual perception that is mediated by such displays is treated in detail in part IV. 

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Chapter 7

The Optical Information For Self-Perception

When a point of observation is occupied, there is also optical information to specify the observer himself, and this information cannot be shared by other viewers. For the body of the animal who is observing temporarily conceals some portion of the environment in a way that is unique to that animal. I call this information propriospecific as distinguished from exterospecific, meaning that it specifies the self as distinguished from the environment.

The Specifying of the self by the field of view

The field of view of an animal, as I will use the term, is the solid angle of the ambient array, is bounded; it is a sort of sample of the whole sphere. The angular scope of the field of view depends on the placement of the eyes in the head,  some animals having lateral eyes and a nearly panoramic field of view and others having frontal eyes and a roughly hemispherical field of view (Walls, 1942, Ch. 10). Horses belong to the first group and humans to the second. In both ocular systems, the separate fields of view of the two eyes overlap in front, but the amount of overlap is very much greater in humans than it is in animals with semipanoramic vision. By the field of view, I mean the combined fields of view of the two eyes.

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…the edges of the field of view are unlike the edges of a window inasmuch as, for the window, a foreground hides background whereas, for the field of view, the head of the observer hides the background. Ask yourself what it is that you see hiding the surroundings as you look out upon the world – not darkness surely, not air, not nothing, but the ego!

Whenever a point of observation is occupied by a human, about half of the surrounding world is revealed to the eyes and the remainder is concealed by the head.

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The purpose of vision, I shall argue, is to be aware of the surroundings, the ambient environment, not merely of the field in front of the eyes. The ambient information is always available to any observer who turns his or her head. Visual perception is panoramic and, over time, the panorama is registered.

There are other remarkable features of the field of view besides its oval boundaries. Still other occluding edges appear within it, those of the nose, the body, the limbs, and the extremities…

The experience of the central self in the head and a peripheral self in the body is not therefore a mysterious intuition or a philosophical abstraction but has a basis in optical information.

Note - …There are always two fields of view available to any animal with two eyes. That is, there are two ambient optic arrays at two different points of observation, each of which is sampled by one eye. Since the points of observation are separated by the interocular distance, the optic arrays are different. I term this difference disparity, by analogy with the retinal disparity studied so intensively by physiological image optics.

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Each individual sees a different self. Each person gets information about his or her body that differs from that obtained by any other person.

NONVISUAL INFORMATION ABOUT THE SELF

The point I wish to make is that information about the self is multiple and that all kinds are picked up concurrently. An individual not only sees himself, he hears his footsteps and his voice, he touched the floor and his tools, and when he touches his own skin he feels both his hand and his skin at the same time. He feels his head turning, his muscled flexing, and his joints bending. He has his own aches, the pressures of his own clothing, the look of his own eyeglasses – in fact, he lives within his own skin.

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EGORECEPTION AND EXTEROCEPTION ARE INSEPARABLE

The optical information to specify the self, including the head, body, arms, and hands, accompanies the optical information to specify the environment. The two sources of information coexist. The one could not exist without the other. When a man sees the world, he sees his nose at the same time; or rather, the world and the nose are both specified and his awareness can shift. Which of the two he notices depends on his attitude; what needs emphasis now is that information is available for both.

The supposedly separate realms of the subjective and the objective are actually only poles of attention.   

Self-perception and environment perception go together.

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THE INFORMATION FOR THE PERCIEVING OF DEPTH

The gradient [of depth] is also anchored at another limit, by the forms projected from the nose, body, and limbs. The nose projects at the maximum of nearness just as the horizon projects at the maximum of farness.

The nose is here. It projects the largest possible visual solid angle in the optic array. Not only that, it provides the maximum of crossed double imagery or crossed disparity in the dual array, for it is the farthest possible edge to the left in the right eye’s field of view. This also said that to look at the nose one must converge the two eyes maximally. Finally, the so-called motion parallax of the nose is an absolute maximum, which is to say that, of all the occluding edges in the world, the edge of the nose sweeps across the surfaces behind it at the greatest rate whenever the observer moves or turns his head.

…the nose provides an absolute base line, the absolute zero of distance-from-here.

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The combined field of view of the two eye sockets (and all higher animals have two eyes) consists of two samples of the ambient array. They overlap more or less, more in humans than in horses, and thus the same structure is included in both segments. But it is not quite the same structure, because the two points of observation are slightly separated and there is a resulting disparity of the two structures. This disparity, or mismatch, is at a maximum for the contour projected from the edge of the animal’s nose, as I pointed out above. The edge of the nose is the left-hand edge of what the right eye sees but the right-hand edge of what the left eye sees, and this maximum mismatch constitutes information for the zero of distance, that is, for the awareness of oneself at the center of a layout of surfaces receding from here. The minimum of mismatch is at the horizon.

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SUMMARY

Perception has two poles, the subjective and the objective, and information is available to specify both. One perceives the environment and coperceives oneself.

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Chapter Nine

EXPERIMENTAL EVIDENCE FOR DIRECT PERCEPTION: PERSISTING LAYOUT

Direct perception is what one gets from seeing Niagara Falls, say, as distinguished from seeing a picture of it. The latter kind of perception is mediated. So when I assert that perception of the environment is direct, I mean that it is not mediated by retinal pictures, neural pictures, or mental pictures. Direct perception is the activity of getting information from the ambient array of light. I call this a process of information pickup that involves the exploratory activity of looking around, getting around, and looking at things. This is quite different from the supposed activity of getting information from the inputs of the optic nerves, whatever they may prove to be.

Suggesting we need to move closer to things – close-up

EVIDENCE FOR THE DIRECT PERCEPTION OF SURFACE LAYOUT

The theory of depth perception assumes that the third dimension of space is lost in the two-dimensional retinal image. Perception must begin with form perception, the flat patchwork of colours in the visual field. But there are supposedly cues for depth, which, if they are utilized, will add a third dimension to the flat visual field. A list of the cues for depth is given in most psychology textbooks: linear perspective, apparent size, superposition, light and shade, relative motion, aerial perspective, accommodation (the monocular cues), along with binocular disparity and convergence (the binocular cues).

…in the end I came to believe that the whole theory of depth perception was false.

…perception does not begin with two-dimensional form perception. Hence, there is no special kind of perception called depth perception, and the third dimension is not lost in the retinal image since it was never in the environment to begin with. It is a loose term. It depth means the dimension of an object that goes with height and width, there is nothing special about it. Height becomes depth when the object is seen from the top, and width becomes depth when the object is seen from the side. If depth means distance from here, than it involves self-perception and is continually changing as the observer moves about. The theory of depth perception is based on confusion and perpetuated by the fallacy of the retinal picture.

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Chapter Twelve

Looking With The Eyes and The Head

Looking around and Looking at

The reason why humans must turn their heads in order to look around is that their eyes are set in the front of their heads instead of on either side, as they are in horses or rabbits. The orbits of the human skull are frontal, not lateral.

It has been suggested that animals who are preyed upon need a more panoramic field of view, whereas predatory animals such as cats can afford to have eyes in the front of the head (Walls, 1942). It has also been argued that the frontal eyes of primates living in the trees afford better “depth perception,” but this argument presupposes the entrenched fallacy of depth perception that this book has been at such pains to destroy.

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There has to be some gap in the combined field of view simply because the body of the animal itself is there, that is, its body is bound to hide some of the surfaces of the surrounding environment.

The portion of the environmental layout that is hidden by the body is continually interchanging with the unhidden remainder as the head turns and the body moves.

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The seeing of oneself is not a complex intellectual experience but a simple primitive one. The orthodox dogma that no animal but the human has self-consciousness is surely false.

With What Does One See the World

The eye is considered to be an instrument of the mind, or an organ of the brain. but the truth is that each eye is positioned in the head that is in turn positioned on a trunk that is positioned on legs that maintain the posture of the trunk, head, and eyes relative to the surface of support. Vision is a whole perceptual system, not a channel of sense (Gibson, 1966b). One sees the environment not with the eyes but with the eyes-in-the-head-on-the-body-resting-on-the-ground. Vision does not have a seat in the body in the way that the mind has been thought to be seated in the brain. the perceptual capacities of the organism do not lie in discrete anatomical parts of the body but lie in systems with nested functions. 

Even so, it might be argued, one surely looks with the eyes even if one does not see with the eyes. But looking with the eyes alone is more looking at, not looking around. It is the scanning of an object, a page of print, or a picture. One also looks with the head, not just with the eyes, more exactly with the head-eye system, as I said at the outset.

The exclusive concern with eye turning is one of the deep errors of the snapshot theory of vision and goes back at least a century.

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The Awareness of the Environment and the Ego

The visual field has boundaries, roughly oval in shape, and it extends about 180° from side to side and about 140° up and down. The boundaries are not sharp, but they are easily observed when attended to. The visual world, however, has no such boundaries; it is unbounded, like the surface of a sphere extending all the way around me.

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The field of view of the two eyes is a sort of mixed cross-section of the overlapping solid angles registered by the eyes. The field of one eye would correspond to a plane picture cutting the solid angle for that eye.

…But the visual world is a kind of experience that does not correspond to anything, not any possible picture, not any motion picture, and not even any “panoramic” motion picture. The visual world is not a projection of the ecological world. How could it be? The visual world is the outcome of the picking up of invariant information in an ambient optic array by an exploring visual system, and the awareness of the observer’s own body in the world is a part of the experience.

The visual Ego

The ambient optic array is then altered, for it includes a solid angle filled by the observer, having a boundary that is unique to the observer’s particular anatomy. It is called the blind region in physiological optics. But it is blind only for exteroception, but not for proprioception. It looks like oneself. Its shape depends on the shape of one’s nose, the shape of ones head, and the shape of one’s limbs. It is altered when a person puts on eyeglasses or when a horse is made to wear blinders. Thus, whenever a point of observation is occupied, the occupier is uniquely specified, whether adult or child, monkey or dog. 

Undoubtedly, the length of a man’s nose determines how he sees himself. (Consider the ego of a baboon in this respect, and think of what the ego of an elephant would be!) For us, the nose is the leftward edge of the right eye’s field of view and the rightward edge of the left eye’s field of view. Hence, it yields a kind of subjective sensation called a double image in the theory of binocular vision, in fact, the maximum limit of crossed diplopia. It would therefore be a theoretical zero for the dimension of distance from here.

This will help explain what the Oakes brothers observed, and also what I wrote about Walters’ Study from Life

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How Does the Eye-Head System Work? Outline of a New Theory

The eyes rotate in rapid jumps from one fixation point to another, and these are called saccadic movements. In terms f the retinal image theory, the fovea of each retina is moved so that an image of the particular “object of interest” falls on the retinal point of highest acuity where the photoreceptors, the cones, are most densely packed together. The anatomical fovea corresponds to the physiological “center of clearest vision.” The fine details of the optical image are said to be the best “resolved” at the fovea.

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A Reconsideration of Eye Movements

Fixation    The prolonged fixing of the eyes on an “object or part of an objects,” the bringing of its image to the fovea and keeping it there, does not occur in life. It is a laboratory artifice, brought about when an experimenter tells an observer to stare at a “fixation point” that is usually of no interest to her. No one stares at a fixed point in the world for long unless she is so preoccupied that she is actually not seeing what she looks at.

Perhaps the general conclusion should be that an eye-posture is nothing but movements that are very small.

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The dual ocular system registers both the matching of structure between the optic arrays at the different points of observation of the two eye and the perspective mismatch of their structure, both the congruence and the disparity, at the same time. The two eyes are not two channels of sensation but a single system. The converging and diverging of the eyes presumably work in the interests of picking up the congruity/disparity information.

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Note that two arrays could not possibly be fused in the sense of being united in one location. Neither could two optical images be mixed or combined. They do not need to be. The fallacy of the traditional theory comes from supposing that two physiological images have to be fused in the brain, as if one picture were picked up and superposed on the other and then compared, in the manner of a photographer who puts one transparent film on top of another and looks to see if they match. The error is to assume that a unitary mental image can only arise from a unitary brain image, a process in the brain that occurs in one locus.

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Chapter Fifteen

Pictures and Visual Awareness

…pictures are as essential a part of human life as words. They are deeply puzzling and endlessly interesting. What are pictures, and what do they do for us? There are obviously two kinds: still pictures and motion pictures.

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…the artist as much as the psychologist, was experimenting with perception all along, even if not formally.

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Vision is simplest when it fulfils its function, not when it meets the criterion of one-to-one projective correspondence in geometry. Its function is to help the observer cope with the environment.

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What is a Picture? The Picture as a Record

A picture is also a record. It enables the invariants that have been extracted by as observer – at least, some of them – to be stored, saved, put away and retrieved, or exchanged. Pictures are like writing inasmuch as they can be looked at again and again by the same observer and looked at by many observers. They allow the original observer to communicate in a fashion with unborn generations of other observers. Art museums, like libraries, are storehouses of knowledge, and they permit knowledge to accumulate. Pictures convey knowledge at second hand and thus are efficient methods of teaching the young. 

Links to things Hockney says about knowledge being passed from early man to know through the art that’s left behind.

Any picture, then, preserves what its creator has noticed and considers worth noticing. Even when she paints a fiction or a fantasy, she does it with invariants that have been noticed in the course of learning to perceive.

A Theory of Drawing and its Development in the Child

Let us consider this remarkable business of preserving what one is aware of; let us try to understand it. Cro-Magnon man drew pictures of what interested him on the walls of caves, and people of all cultures have been drawing pictures ever since. All of us can draw, even those who never learnt to write. Writing was not invented until our ancestors learnt to record their words on a surface, and that is harder to learn than recording awareness. Ideographs and syllabaries and alphabets would never have been devised if people had not already been drawing for thousands of years.

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Of all hand-held tools that have been invented, the sort that makes traces on a surface is especially noteworthy – the stylus, brush, pen pencil, crayon, or marker. The movement of the tool over the surface is both felt and seen.

The young child practices the fundamental graphic act in sand, mud, or a plate of food, to the dismay of his parents. When given a tracing tool, the child uses it on approved surfaces as soon as he can hold the tool, beginning at around eighteen months of age. The permanent trace is what interests the child.

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Copying is fundamentally the act of making traces on a surface that coincide with the traces on another surface, either one surface overlaid on another or one that could be overlaid on another.

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Making a perspective drawing of a scene on a sheet of glass is a special case of coincidence-tracing. This was the method of artificial perspective discovered by the painters of the Renaissance and recommended by Leonardo da Vinci. It involves setting up the glass as if it were a window and then, with one eye exactly fixed in front of the window, drawing lines on the surface to coincide with the projections of the occluding edges of the layout, the edges and corners of the layout (the dihedrals), and the fissures, sticks, and pigment borders.

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The Muddle of Representation

If this new theory is correct, the term representation is misleading. There is no such thing as a literal re-presentation of an earlier optic array. The scene cannot be re-established; the array cannot be reconstituted. Some of its invariants can be preserved, but that is all. Even a photograph, a colour photograph at its technological best, cannot preserve all the information at a point of observation in a natural environment, for that information was unlimited.

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What about the Illusion of Reality? The Duality of Picture Perception

A picture is not like perceiving. Nevertheless, a picture is somehow more like perceiving an object, place, or person than is a verbal description. The illusion of reality is said to be possible.

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The eye is easily deceived, and our faith in the reality of what we see is therefore precarious. For two millenniums we have been told so.

The purveyors of this doctrine [above] disregard certain facts. The deception is possible only for a single eye at a fixed point of observation with a constricted field of view, for what I call aperture vision. This is not genuine vision, not as conceived in this book. Only the eye considered as a fixed camera can be deceived. The actual binocular visual system cannot. A viewer can always tell whether he looking at a picture or at a real scene through a window.

The information displayed is dual. The picture is both a scene and a surface, and the scene is paradoxically behind the surface. This duality of the information is the reason the observer is never quite sure how to answer the question, “What do you see?” For he can perfectly well answer that he sees a wall or a piece of paper. It is this duality in the optic array from a picture that makes the drawing a bad way to begin the study of perception.

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No painter and no photographer should ever strive to give viewers the feeling that they are looking at a real place, object, person, or event. There is no need to do so. In any case, the effort is bound to be a failure.

I conclude that a picture always requires two kinds of apprehension that go on at the same time, one direct and the other indirect. There is a direct perceiving of the picture surface along with an indirect awareness of the virtual surface – a perceiving, knowing, or imagining, as the case may be.

The Power of Perspective in Painting

The advocates of perspective representation are mistaken, but those who reject perspective as a mere convention are also mistaken. There is complete confusion on both sides. The terms in which that debate has proceeded are thoroughly misleading.

The dogma that linear perspective adds depth to a picture along with the other kinds of perspective that are “cues” for depth is a source of endless confusion. The term perspective is generally misunderstood. The theory of projection on a transparent picture plane to a stationpoint is a Renaissance discovery that is properly called artificial perspective. The theory of the ambient optic array from an environment to a point of observation should be called natural perspective and is not at all the same thing.

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These are metaphors to describe the powerful experience aroused by the picture that locates the observer in a virtual environment: one is taken out of oneself; one is transported; one is set down in a far place. The place may be a distant part of the real environment or another world. Travel pictures take one to where the traveller has been. Battle pictures take one into the heart of the melee. Historical pictures take one to the forum of ancient Rome. Religious pictures take one straight to heaven, or hell. The viewer sees himself in the environment, for it extends out beyond the frame of the picture.

Is Depiction a From of Description?

It is troublesome for a painter to follow the prescriptions of artificial perspective, as any serious work on the subject clearly shows (e.g., Ware, 1900). Even when the prescriptions are followed it is impossible to enforce the rule for the beholder, for no viewer could be expected to maintain one eye ate the proper station point in the air in front of the picture, even if the art gallery provided a bite-board or headrest to specify the viewpoint for each painting hung.

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…why bother to master all that geometry? It was a complicated and controversial business in any case. Visual scientists with all their theorizing know little about the actual act of painting. a fine art should not be subject to rules and regulations. This is the attitude of many modern painters and most schools of art.

…the essence of a picture is just that its information is not explicit. The invariants cannot be put into words or symbols. The depiction captures an awareness without describing it. The record has not been forced into predications and propositions. There is no way of describing the awareness of being in the environment at a certain place. Novelists attempt it, of course, but they cannot put you in the picture in anything like the way the painter can.

This is where the PhD thesis might be useful – to combine with the pictures to make explicit the knowledge gained by making them?

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The Consciousness of the Visual Field

My comparison of the visual field to a perspective painting, although guarded, now seems to me a serious mistake. No one ever saw the world as a flat patchwork of colours – no infant, no cataract patient, and not even Bishop Berkeley or Baron von Helmholtz, who believed firmly that the cues for depth were learnt.

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Drawing in perspective does depend on viewing in perspective, it is true, but this only means that drawing requires the learner to notice the edges of the layout confronting him, especially the occluding edges.

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…mostly what is lost in a picture, drawing, painting, or photograph is the information that can be extracted only from the changing perspective structure of the ambient optic array of a moving observer.

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When young children learn to draw, they certainly do not begin by drawing their sensations in patchwork perspective and then progress to the stage of drawing their concepts. But neither do they begin by drawing their concepts and then progress to the stage of drawing their sensations. They simply draw the invariants they have learned to notice.

A picture is a record of what its creator has seen or imagined, made available for others to see or imagine.

Use this to define what ‘picture’ means

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CONCLUSION

It [the ecological approach to perception] begins with the flowing array of the observer who walks from one vista to another, moves around an object of interest, and can approach it for scrutiny, thus extracting the invariants that underlie the changing perspective structure and seeing the connections between hidden and unhidden surfaces. This approach next considers the fact of ambient awareness and explains it by the invariance of the sliding samples of the 360° array.

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The artificially produced glimpse is an abnormal kind of vision, not the simplest kind on which normal vision is based. It is a poor sort of awareness. But it has seemed to be fundamental for hitherto persuasive reasons: it results from an image; it comes from a stimulus; it is a sensory input; it is what the nerve transmits. But if this is so, how could the series of glimpses be incorporated? How could the sequence, as I put it, be converted into a scene?

But if, on the other hand, perception of the environment is not based on a sequence of snapshots but on invariant-extraction from a flux, one does not need to have ideas about the environment in order to perceive it.  

Another puzzle is resolved at the same time, the awareness of oneself in the environment. The young child does not need to have ideas of space in order to see the surfaces around him; he need pay no attention to the cues for depth if he can see the layout; he need not compensate for the small retinal image of a distant surface if he never notices the image but only extracts the invariant.

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[The experimenter] could not create the illusion of looking around and walking through the countryside in any case, for he would have to create the countryside. He should not want to deceive the observer. The observer who begins to be fooled should be allowed to make the standard tests for reality, such as getting up and looking behind the screen of the display.

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