SPATIAL PROPERTIES OF SHEAR DISPARITY PROCESSING

We investigated whether vertical-shear disparity was extracted from th e whole visual field or from a more local area and how global estimate s of vertical disparity are derived, We also investigated the role of cyclovergence in processing shear disparity, Random-dot stereoscopic d isplays in various configurations were presented with horizontal-shear disparity, vertical-shear disparity or same-sign horizontal- and vert ical-shear (rotation) disparity. Vertical-shear disparity introduced i nto only the right half of a 60 deg-wide display produced perceived in clination of the whole display when the center of shear was on the fov ea, but did not produce inclination, either of the whole display or of a local area when the centre of shear was in an eccentric retinal pos ition, A display containing dots with vertical-shear disparity mixed w ith dots with zero-disparity produced one inclined surface, Horizontal -shear disparity always produced inclination confined to the local are a of disparity, Rotation disparity produced no inclination when introd uced into the whole display, but when introduced with zero-disparity d ots it produced an inclined plane distinct from the plane defined by t he zero-disparity dots, These results could be attributed to cycloverg ence, which we therefore eliminated in our last experiment. We conclud e that the perception of surface inclination is based on the differenc e between local horizontal-shear disparity and global vertical-shear d isparity averaged over the whole visual field. Copyright (C) 1996 Else vier Science Ltd