RELATIVE SHEAR DISPARITIES AND THE PERCEPTION OF SURFACE INCLINATION

A dichoptic display in which the images are cyclorotated in opposite d irections does not appear inclined. This suggests that perceived incli nation depends pn the difference between horizontal-shear and vertical -shear disparity. Large random-dot stereoscopic displays were presente d with various types of shear disparity. Perceived inclination was the same magnitude for horizontal and vertical shear disparities. Opposed horizontal and vertical shear produced greater inclination than a sin gle-axis shear. Same-sign vertical and horizontal shear (rotation) pro duced no inclination. These results support the relative-shear hypothe sis. Cyclovergence was measured and was insufficient to account for th ese effects. We conclude that perceived inclination depends on the dif ference between horizontal- and vertical-shear disparities. Perceived inclination was not based on vertical disparity within small displays or within large displays with a zero-disparity surround. Relative-shea r disparities are therefore extracted globally rather than locally.