Perception of partly occluded objects and illusory figures: Evidence for an identity hypothesis.

Abstract

Three experiments test the hypothesis that perception of partly occluded figures (POFs) and illusory figures (IPs) derive from a single visual interpolation process. In each, 2 magnitude estimation tasks were used. One assessed perceived unity of visible parts of POFs; the other perceived clarity of edges in IF displays. Exps. 1 and 2 tested the effects of relative positions and orientations of edges on perceived unity and clarity. Exp. 3 used randomly generated displays to test whether edge relations sampled at random would exert the same effects on POFs and IFs. All studies showed nearly perfect correlations between perceived unity and perceived edge clarity, when the physically specified parts of the figures were identical. The specific conditions under which edges are interpolated fit well with predictions of a recent theory (Kellman & Shipley, 1991). These results suggest that a single unit-formation process underlies modal and completion. Perceptual representations are said to go beyond the information given when some of their contents have no local stimulus determinants. Ordinary object perception is a conspicuous example. Although most viewed objects are partly occluded by others, their boundaries are for the most part accurately perceived. Michotte. Thines. and Crabbe (1964) termed this ability perceptual completion and distinguished two types. Modal refers to the presence of sensory attributes; subjects do not differentiate between part? which have been added and those which have a physical correlate. These additions have the same visible attributes or 'modes' (brightness and hue) as the rest of the figure, hence the term 'modal'. The perception of parts of objects without local sensory attributes (e.g., as a result of occlusion) was designated amodal completion. According to Michotte et al.; The word 'amodal' is used here with a primarily negative meaning: it is intended to imply that the completed portion wholly lacks visible attributes. Nonetheless, the completion is perceived; it is neither an inference nor a projection of some mental image, but a direct perception.