TYPES OF SHEAR DISPARITY AND THE PERCEPTION OF SURFACE INCLINATION

A study is reported of (i) the perceived inclination of a textured sur face in depth about a horizontal axis as a function of disparity magni tude for horizontal-shear disparity, vertical-shear disparity, and rot ation disparity; and (ii) interactions between patterns with shear or rotation disparity and superimposed or adjacent patterns or lines with zero disparity. Horizontal-shear disparity produced strong inclinatio n which was enhanced by superimposed or adjacent zero-disparity stimul i. It produced little or no inclination contrast in superimposed or ad jacent zero-disparity stimuli. Vertical-shear disparity produced incli nation in the opposite direction (induced effect) which was reduced to near zero by a superimposed zero-disparity pattern. Adjacent vertical -shear and zero-disparity patterns appeared inclined at slightly diffe rent angles with a wide curved boundary. This suggests that vertical-s hear disparities are averaged over a wide area. Rotation disparity pro duced minimal inclination. A superimposed or adjacent zero-disparity l ine appeared strongly inclined. A superimposed or adjacent zero-dispar ity pattern appeared vertical and caused the pattern with rotation dis parity to appear inclined. Four mechanisms are proposed to account for the results: depth contrast, depth enhancement, deformation-disparity processing, and disparity transfer arising from cyclovergence.