Story of Psychology - Morton Hunt [307]
Such a one was the late James J. Gibson (1904–1979), whose admirers considered him “the most important student of visual perception of the twentieth century” and “the most original theoretician in the world in the psychology of perception,” but whose theory is considered by the majority of perception specialists “extremely implausible” (one reviewer even called it too “silly” to merit discussion) and has few advocates.68
Born in a river town in Ohio and reared in various parts of the Midwest, Gibson was the son of a railroad surveyor.69 He went to Princeton University but felt out of place in a social world that revolved around clubs, and preferred to associate with what he called “the eccentrics.” For a while he vacillated between philosophy and acting (he was wavy-haired, square-jawed, and good-looking enough for leading roles), but in his senior year he took a course in psychology and at once heard the call. In 1928, he received a faculty appointment at Smith, where for some years, he was interested in relatively traditional perception research. Then, during World War II, he was asked by the Army Air Corps’s Aviation Psychology Program to develop depth-perception tests for determining who had the visual aptitudes needed for flying, particularly for making successful take-offs and landings.
He considered the classical cues to depth perception, including shadows and perspective, of little worth. In his opinion they were based on paintings and parlor stereoscopes rather than on three-dimensional reality, and on static images rather than on movement. What seemed to him much more useful and realistic were two other kinds of cues: texture gradient, like the uniformly changing roughness of the runway as seen by a pilot during the final leg of an approach; and motion perspective, or the flow of changing relationships among objects as one moves through the environment, including all that a pilot sees during take-offs and landings.70 These cues soon became, and are today, accepted components of the cue-based theory of depth perception.
Gibson’s Air Corps work held the germ of his later view. The crucial mechanism in depth perception (in all perception, according to Gibson) is not the retinal image, with all its cues, but the changing flow of relationships among objects and their surfaces in the environment that the perceiver moves through. During the 1950s and 1960s, he did a considerable amount of research at Cornell that tested his belief in texture gradients. In some experiments he placed diffusing milk-glass between an observer and textured surfaces; in others he dilated the observer’s eyes to prevent sharp focus on texture; in still others he cut Ping-Pong balls in half and made goggles of them so that what his subjects saw was foglike, without surfaces or volume.71 From these and other experiments, plus a careful consideration of his research on air-crew testing and training, Gibson came to reject texture gradients and to stress movement by the observer through the environment as the key to depth perception. However large or small the movement, it results in changes in the optic array—the structured pattern of light reaching the eye from the environment—such as is suggested in this drawing:
FIGURE 35
How optic array conveys depth
The optic array, rich in information as seen from any point, becomes infinitely richer with movement by the observer. Even minor movements of the head change the array, transforming what is seen of an object and the relationships among objects, and yielding optic flow of one kind or another. Gibson came to believe that optic array and flow convey depth and distance directly, without the need of mental calculation or inference from cues.72
This is how Gibson explained depth perception in his sweeping “ecological” theory of “direct perception.” The pity is that he felt obliged to throw out the baby with the bathwater. For it is possible to acknowledge both the neural and cognitive views of depth