G IBSON ’ S T HEORY
G IBSON ’ S T HEORY
Gibson’s theory of perception is based on information. As Reed (1988) notes, this is in contrast to sensation theories with their thorny psychological and episte- mological problems. Perception is “direct” since ecological information specifi es its source. Gibson (1966) viewed visual information as optical, residing in the naturally arising structure of the optical array. In other words, perception is not internal, not based on “having sensations” but on directly “detecting information” available in the ambient light.
What we perceive are “affordances,” the functional properties of objects, spaces, and events. We perceive affordances of things for behavior, offerings that can be detected and used by observers. These affordances are not abstract physi- cal properties, but functional, ecologically relevant properties, such as texture or manipulability. Affordances are offerings, not requirements (for example, we can remain standing when an object affords sitting). A specifi c object may have many affordances and these are detected by the perceiver who becomes directly aware of external optical ecological information. Each perceived affordance has its own meaning and use for the individual who, thus, learns to differentiate the meaning of an object in terms of its relevance to one’s activities and needs. Affordances are not possibilities, but real and external facts. Nor are they subjective. A particular object may yield different affordances to different individuals precisely because affordances are functional, that is, related to both the person and the environment.
Because we perceive affordances of things for behavior, affordances for action, perception is always simultaneously of the self and of the environment. In other words, we each perceive ourselves in the natural world. As Reed (1988, p. 280) explains, the purpose of perception is to keep observers in contact with their sur- roundings, where the organized environment is replete with information capable of supporting perception and where observers either succeed or fail to adequately perceive this information.
Instead of distinguishing between space and time, Gibson uses the concepts of persistence and change as reciprocals. The layout of a particular place is typically permanent in that some features, such as the ground, sky, and other substantial sur- faces, persist for the longer term. For Gibson, changes in the qualities of substantial surfaces, (shape, position, composition, texture, color, etc.) count as ecological events. As Reed (1988, p. 286) points out, an object is a group of substantial surfaces forming
284 Joan M. Preston
a topologically discrete entity that persists for a minimal time and undergoes its own characteristic change. Although places and objects are persistent, information changes as the individual moves through the environment. Movement produces a perceptual fl ow of optical information. Each gradient is visible only from a specifi c point of observation. As we navigate, then, we have a “path of view” of our envi- ronment where information about objects and events persists or changes. As we move, some hidden objects become visible while others are occluded.
Every observer has a path of view and, although individual paths of view are changing, the set of all possible paths of view persists. As Reed (1988) summarizes, the environment is public and persistent. That is, “the transition between what is visible from here now (a single observation point) and what is visible in ambula- tory perception (the observable habitat)—which amounts to the connectedness of the layout of the environment of all animals—is itself visible” (p. 289). As Gibson proposed, because experience is based on awareness over time, we can explore and share our environment. We perceive ourselves inhabiting the environment due to invariant and perspective structures. From a given point of view, we see a unique optic array, with some parts occluded and with particular perspectives of the visible parts. As we move, the occlusion relationships and the perspective forms change. These changes are the perspective structure of the array, a kind of optical fl ow spec- ifying the path of locomotion. The invariant optical structure is whatever persists despite changes in the perspective structure. Perspective structures specify where we are going and invariant structures specify what is ahead.
Instead of cognitive maps for navigation, Gibson viewed locomotion as per- ceptual control of action, that is, movement through cluttered semi-enclosures involving perception of objects and their affordances. Individuals orient to the per- sisting features of the layout and perceive that they can reach a place if the nested places through which they must pass are suffi ciently open and provide surfaces that are continuously supported.
As we move along a path, objects that we pass disappear from sight behind us, while new vistas open up in front when previously hidden objects become visible. Each vista is what is seen from “here,” but here is an extended region, not a point. Vistas are serially connected in that the end of one opens up to another, and this connectivity persists. Hidden aspects of a particular vista are not necessarily invis- ible, but to fi nd the occluded, we need to detect the continuity between the visible and the hidden. Gibson pointed out that cluttered environments offer a choice of vistas and, to fi nd a hidden place, we need to see which vista must be opened next, which occluding edge hides the goal.
Shared awareness occurs because we all perceive the persisting environment specifi ed by the invariant structure of the optical array and, as we move, we perceive our own changing points of view specifying the environment’s perspective struc- ture. Representations evolved in this context of shared awareness as social mediators. Representations are the results of processes of information selection and display by
11 Mediated Environments to Consciousness
the creator/speaker that make others aware of something. Representations permit affordance meaning to be perceived indirectly, and humans have developed various means for marking surfaces (writing, drawing; painting, electronic media) and com- municating with voice, gesture, sound-making devices, etc.
Gibson stated that we perceive the self inhabiting the environment, not just our own path of view but those of all observers. Having a point of view/ path of view is an ecological fact rather than a physical (or mental) fact. A spe- cifi c point of view produces a unique optic array. Motion perspective specifi es the path of locomotion, thus perspective structure is a kind of optic fl ow, in contrast with traditional perspective that specifi es a point of view. Each person’s locomotion changes the perspective structure of the optical array (i.e., changes occlusion relationships) for that individual. In spite of the changes of perspective structure, some aspects of the optical pattern persist and these are the invariant structure. Gibson argues that the invariant structure in an array specifi es what any observer on any path would see. It is the invariant structure that specifi es the environment independently of the self.
Gibson’s theory of perception explains shared awareness using perspective structure and invariant structure. The perspective structure specifi es the changing environment, the changing points of view, as the observer moves. The persisting environment is specifi ed identically to all observers by the invariant structure of the optical array. Thus, we can share awareness while simultaneously having our own point of view. Perception is both informational and social. Our shared aware- ness provides the context for the evolution of representations, including pictures, symbols, signals, and so forth. We are all able to display information to make it available to others. However, Gibson distinguished between information-based vision and derived information, or representation-based information that is depen- dent on cultural conventions. When information specifying affordance meanings is available in the environment, they can be perceived directly. Information in rep- resentations is perceived indirectly. Pictures, language, fi lm, and other media are meaningful in a way that is part ecological, but also partially cultural and narrative. Reed (1988) has pointed out that Gibson clearly indicated that “mediated appre- hension gets combined and used with direct apprehension.” For humans, direct and indirect perception, individual and social awareness, are always mixed, although direct perception is primary.