December 1977
A Tentative Formula for the Perception of Persistence and Awareness of Reality
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 References to these essays must cite them explicitly as unpublished manuscripts.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.
The perception of persistence should not be confused with the persistence of perception. The latter arises because of afterimages, memory images, traces, or anagrams, i.e., residues of some sort.
The awareness of going-out-of-sight by occlusion is a case of perceiving the persistence of a surface. There is information for persistence (cf. Michotte, Gibson, Kaplan).
The awareness of going-out-of-existence by destruction is a case of perceiving the non-persistence of a surface. The cases can be distinguished. (But, of course, destruction may occur out of sight.)
A criterion for an existing surface is that it can project a visual solid angle to some point of observation in the illuminated medium of a cluttered environment. If it does not, it is nonexistent (unreal, imaginary). An existing surface can therefore come into and go out of sight by a shift of the point of observation. A nonexistent surface cannot.
Children presumably learn very readily to distinguish between real and imaginary surfaces (places, persons, events) that they see or imagine for themselves, by this criterion and others similar to it. They do not confuse “subjective and objective reality” as the classical theory of imagery leads us to assume.
What they cannot do is apply these automatic criteria to surfaces that are depicted or described for them by others and that cannot be scrutinized at first hand. The distinguishing of fact and fiction then becomes a matter of rational and social criteria, of evaluating pictures and predictions.
No wonder, then, that the psychological study of the varieties of non-perceptual awareness is full of perplexities.
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Either (1) Perception must be sustained by a persisting sensory input, since all perception is “sense perception.” Any persistence of perception after the stimulation senses is the result of an afterimage, or an “immediate” memory image, or some other kind of memory image the nature of which is not yet agreed on.
Or (2) Perception need not be sustained by a persisting sensory input, since it consists of registering invariants and variants, not of processing inputs. One proof is that we perceive a layout of surfaces only some of which are in sight at any given moment. That is, the perceiving of persistence depends on information not on the persistence of vision after stimulation ceases.
(3) What, then is memory?