What gives rise to the perception of motion?

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The assumption that displacement of the retinal image over the retina is the basis for all perception of motion is rejected. The reasons for the plausibility of this assumption are considered. It is part of the traditional theory that retinal sensations are entailed in visual perception. But it involves a misconception of how the eyes work. Another theory of the information for perceiving motion is proposed in terms of the ambient array of light. The registering of subjective bodily movements by vision is contrasted with the detecting of objective environmental motions. A number of century-old puzzles are resolved by this approach and a set of novel experiments is suggested. Experimental studies of the perception of motion in the past, especially of visual motion, have failed to resolve the old puzzles or to yield any kind of general explanation. The root of the trouble may be a persistent misconception of what gives rise to the perception—an erroneous but plausible assumption about the stimulus. What is the effective stimulus that always elicits a sensation or perception of motion? The physical motion of an object in the world, one might answer, but this is obviously not sufficient unless the object is illuminated or luminous, and unless it lies within the field of view of the observer. The motion must be specified somehow in the light to an organism and it must also enter an eye. When it is specified in the light and does enter the eye the animal almost always detects it, as the 1 This summary is based on a series of investigations over the last 10 years on the perception of motion and space carried out with the support of the Office of Naval Research under Contract NONR 401(14) with Cornell University. A bibliography of the published studies may be obtained from the author. This is the third summary of the project to be published in Psychological Review (Gibson, 1954, 1957). It is hoped that each summary makes some theoretical advance over the previous one. study of behavior shows. This is what is meant by saying that animals are very sensitive to But physical motion is not the same as optical motion.