Visual inhomogeneity and eye movements in multistable perception

For a long time figural multistability has attracted ~e attention of psychologists, because to understand how this phenomenon occurs might help one to understand perceptual processing in general. Figural multistability appears to be a necessary consequence of the normal functioning of our visual system, and hence it is something that any theory of visual processing should be able to account for w.ith recourse to the mechanisms that explain normal, or correct, perception. This interest has generated much research aimed at determining the factors that control the alternation in interpretations inherent in the phenomenon of perce~tual multistability . The roles ofeye movements, type of viewing (either binocular or dichoptic), stimulus contrast, state of light-dark adaptation, focus, mean luminance, and many other factors have been investigated, but th~ resul~ of these research efforts have yielded no conclusive eVIdence in favor of any of these factors' being the cause ofalternations. At best, these studies have proved the existence of some empirical regularities, but they have not offered any explanation for why these regularities should hold; they have failed to provide a deductive link betw~~ the basic properties of the visual system and the empmcal results. Among the factors shown to be involved, eye movements have seemed to be the more likely cause of the alternations, but eye-movement recordings made of subjects inspecting ambiguous figures have not consistently revealed that a change in fixation either follows or precedes an alternation (see Gale & Findlay, 1983). The fact that reversals may also occur voluntarily (see Liebert & Burk, 1985) adds a further complication, because it clearly ~e­ veals that both top-down and bottom-up processes are Involved. Consequently, it is difficult to trace the boundary between what perceptual mul~i~tability o,,:es to early visual processing, and what cogmnve processing adds to it. It is the aim of this note to show how visual inhomogeneity, a well-known and well-established ~ic property of early visual processing, may be responsible for some of the alternations that occur when the eyes move across a multistable figure.