AMODAL COMPLETION IN TEXTURE VISUAL-EVOKED POTENTIALS

Amodal completion refers to the phenomenological finding of perceiving partly occluded objects as continuing uninterrupted behind hn occlude r. The outlying problem is how the visual system processes such non-lo cal stimuli because the known processes of early vision are spatially restricted operations which segregate local differences in the Visual image, and little is known about their interactions in producing the s egmentation of the image into functionally coherent, or global, object s. We recorded human visual evoked potentials (VEPs) to texture stimul i and addressed local/non-local relationships in comparing a condition in which local edges were present, due to texture segregation, with a condition in which, in addition to local edges, textures appeared to continue as surfaces behind gray stripes due to non-local amodal compl etion. Subtraction of offset from onset responses showed: (1) a differ ence component due to texture segregation characterized by a negativit y with onset at about 95 ms and lasting up to about 280 ms; (2) a furt her negativity, specifically elicited by amodal completion, with onset at about 142 ms, peaking at 175 ms, and lasting up to about 188 ms. T herefore, amodal completion occurs at an early processing stage of ima ge analysis and the difference component in VEPs can be related to fig ure-ground perception. (C) 1998 Elsevier Science Ltd. All rights reser ved.