March 1976
Note On Some Types of Visualizing Considered as Extended Forms of Visual Perceiving
J. J. Gibson, Cornell University
The World Wide Web distribution of James Gibson’s “Purple Perils” is for scholarly use with the understanding that Gibson did not intend them for publication. References to these essays must cite them explicitly as unpublished manuscripts. Copies may be circulated if this statement is included on each copy.
I wish to avoid the use of terms like ideas, memories, images mental representations, and thoughts as contrasted with percepts. Instead, I will talk about visualizing of various kinds. I will consider them asextensions of visual perceiving. Perceptual systems are not the same as channels of sensory input. The characteristic activity of the visual system is exploratory looking. This has at least three levels, scanning with the eyes, looking-around with the head and eyes, and going-and-looking with the body and head and eyes. Perceiving normally occurs during locomotor movements of the body and turns of the head. There is a special form of perceiving, to be sure, which occurs with eye-movements only and I will arbitrarily call it seeing. It is a limited kind of perceiving but it is the kind that has been studied by psychologists almost exclusively.
Definitions of Seeing and Perceiving. Seeing is the apprehending of environmental surfaces that face the temporary point of observation and fall within the temporary field of view. The head and body do not move. Perceiving is the apprehending of environmental surfaces in general including those not facing the observer and those outside his field of view. The head and body are mobile as well as the eyes. Perceiving is based on the ambient optic array but seeing is based on a limited angular sample of the array.
According to this definition one perceives the far side of an object, the ground behind an object, and the surface behind a window, but one does not see any of them. Similarly, the parts of the environment behind the head are perceived but not seen. Moreover, things that are too far away, too small, or too large to allow of seeing from here can nevertheless be perceived with a changing point of observation.
The Phenomenal Visual Field. What I called the visual field in 1950, the experience of a patchwork of colored forms, is not the same as the experience of the surfaces that face the point of observation and fall within the field of view. What I was describing was a field of hypothetical sensations, and I now doubt that one can ever experience them, certainly not “pure” sensations. The only way to get even an approximation to sensations, as I admitted, is to maintain fixation of the eyes and then introspect. Even so, the solidity and superposition of the surfaces, their slants and distances from here, cannot be got rid of. Seeing, therefore, is not the having of visual sensations. Seeing with the eyes fixed is an unnatural and restricted form of seeing, just as perceiving with the head fixed is a restricted form of perceiving. Nevertheless, it is the kind of experience that is imposed on an observer when the experimenter uses a tachistoscope, on the assumption that a retinal image is a stimulus.
Seeing from a Fixed Particular Point of Observation. Note that the seeing of the environment entails awareness of a fixed point of observation from which the surfaces are seen, whereas the perceiving of the environment does not. To move about is to perceive at no fixed particular point of observation. We speak loosely of “seeing a thing from all sides,” which is necessary to perceive it properly. Having walked around it, the formless invariants that underlie the changing perspectives can be picked up. The sequence of momentary perspectives contains more information that a single perspective.
The Extending of Perception by Locomotion. Head-turning allows the individual to perceive the environment behind his head. Head-displacements or short locomotions allow the individual to perceive the solidity and superposition of objects and the surfaces behind the occluding edges. Locomotion extends perception. Long locomotions extend it farther out than short locomotions. Note that during locomotion, perception is both prospective and retrospective. The observer has foresight of what is to come and hindsight of what is past. He perceives over time. This way of stating the facts is truer than the orthodox description which says that anything in the past has to be remembered, anything in the future has to be imagined or expected, and only what is “present” can be perceived. The term “span” of memory does not resolve the paradox. Note that the perception of what is ahead and of what is behind are continuously connected with the perception of what is here during locomotion. The perceiving of events in the world, i.e., the motions of objects, is extended in time, of course, whether or not the observer himself moves. For as long as an event is continuous it is perceived as a unit.
The Extending of Perception by Manipulation. Primates like us can also explore the environment by handling things. Children learn to use tools, to take things apart, put them together, turn them around, make them, break them, hide them, and discover them. In all these operations the scope of perceiving is enlarged.
Visualizing
No clear division can be found between perceiving and visualizing. There are many kinds of visualizing but they are all extensions of perceptual knowledge in one way or another. They are not so continuously connected with seeing here-and-now as perceiving is.
1. Hidden surfaces that are at great distances can only be visualized. These are places that are separated from the local vista by many occluding edges. For example, I can perceive the next room, for it is hidden from this room only by one occluding edge at the door. My office however, is a mile away and is separated from this room by twenty or thirty occluding edges. Nevertheless, I have observed the transitions between these vistas many times and the experience is fairly clear. My publisher’s office, however, is five hundred miles away and is separated from what I now see by uncounted occluding edges never attended to. I can only visualize it dimly. This seems to me a better statement than to say I have a faint memory image of it.
2. Hidden surfaces that are separated from what I see now by a long sequence of seeing other surfaces can only be visualized. We say that we have not seen something “for a long time”. For example, I have a pair of climbing boots stored away in the basement of my house. I have not had them in my field of view for two years. I can find them; I am oriented to them; but I can only visualize them. This is better than saying I can retrieve an image of my boots from a storeroom in my mind called “long-term memory”.
3. The places in the habitat that one needs to go because of their affordances can be visualized. For example, right now I can point to my neighbors’ houses, to the grocery store, the post office, and the footbridge to the campus. I can go to any of these places and when I am at one of them I can go to another. And I always know the way home. I am not the only animal capable of this kind of knowledge; a rat has it too. Note that the state of being “oriented” to the places that constitute the environment involves an awareness of the temporary place of observation in it. But one can be aware of places as suchwithout the sense of being in a particular place.
4. The internal parts of opaque things that fit together or are joined together can be visualized if they have been assembled, disassembled, or dissected. Examples are the parts of a clock or the organs of an animal.
5. Things that can only be seen with a microscope are probably visualized rather than seen or perceived. This is an extension of the way we see a very small thing by putting the eye close to it but not continuous with it since the optical instrument intervenes. (What about spectacles, i.e., eye glasses; do they intervene?)
6. Very distant things the details of which can only be seen by means of a telescope are perhaps best said to be visualized. If one could approach the thing one would see it, and by walking around it one could perceive it, but the instrument mediates knowledge.
Knowledge at Second Hand
The mediation of perception reminds us that we can get information from other persons, by means of social communication. We make and use artifacts like maps and pictures. We also make and use verbal descriptions. The problems and their complexities are staggering. All I will attempt is a partial list of the kinds of displays that allow a person to have a sort of vicarious perception of what another person has discovered directly.
Maps. A person who has not explored a habitat by locomotion can nevertheless visualize it to some degree if he consults a map and can “read” it.
Pictures. They permit seeing at second hand but not perceiving at second hand, in my terminology.
Sculptures, models, toys, dolls. They allow the invariant proportions of things to be displayed.
Movies. When the camera is “panned” the display can simulate looking-around; when it is “dollied” the display can stimulate approach or retreat, and locomotion. A movie thus comes closer to perception than any other display, and can extend our perception of the world enormously.
Written description and narration. Writing enables us to visualize objects, animals, people. places, situations, and events, of course, as do the non-linguistic displays of information. In what respects is the information the same and in what respects is it different? Is optical information coded into language?
The Visualizing of Non-existent Things
A surface-based theory of perception has it that things without light-reflecting surfaces do not exist. Things with light-reflecting surfaces do exist as long as they have the surfaces and there are points of observation at which they can be seen. A man can visualize the house he once lived in which has since burned down; he can visualize the house he wants to live in which is not yet built; but these should not be confused with the visualizing and perceiving the house he lives in.
We have various terms for the things without surfaces, imaginary, unreal, fictional, virtual, but they are slippery. We have several words for the corresponding experiences, fantasies, dreams, hallucinations, but they are ill-understood. What are these kinds of visualizing? Here is a tentative list:
1. Things with surfaces that have gone out of, or not yet come into existence.
2. Things in mirrors, virtual objects.
3. Fictional or invented things, places, people, events.
4. Geometrical planes, polygons, and polyhedrons, the ghosts of surfaces and objects.
At least some of these kinds of visualizing are not forms of knowing. They are even further extensions of knowing. How is this?