Possible stimulus hypothesis and visual space perception.

Abstract

For any given retinal projection there is a family of stimuli whose members could each give rise to that projection when appropriately positioned with respect to the eye. Perception theorists often imply that this family of stimuli (and related stimulus positions) specifies the possibilities for perception but have not stated this explicitly. The hypothesis is referred to here as the possible stimulus hypothesis. More specific hypotheses are derived from it. They include Koffka's size-distance and shape-slant invariance hypotheses. It is shown that Koffka's hypotheses are only special cases of more general hypotheses named the size-distance-slant and shape-slant-tilt invariance hypotheses. Implications for perceptual constancy and for tests of invariance hypotheses are indicated. Explanations for the perception of objects in space should be more complex than Helmholtz and Koffka have indicated and Gibson's theory would be more precise and broader in scope if the possible stimulus hypothesis were recognized as an essential part of the theory.