THE ROLE OF ORIENTATION DISPARITY IN STEREOSCOPIC PERCEPTION AND THE DEVELOPMENT OF BINOCULAR CORRESPONDENCE

Abstract

Stereoscopic vision utilizes disparities between the retinal images to determine the distances of objects as well as their three-dimensional shapes and orientations. The detection of horizontal disparity has been generally assumed to underlie stereopsis. It indicates the depth of an object point relative to the point of fixation and in principle, the third dimension of shape and orientation of an object can be derived from the depths of its points. However, other disparity features may also be utilized that directly indicate the orientation of surface in space. When a surface is tilted, its retinal images undergo differential deformation in the two eyes. Tilt about a horizontal axis causes the shearing of the retinal images, while tilt about a vertical axis causes unequal horizontal contractions. These deformations are independent of the fixation distance, which affects only the relative positions of the images, that is, the horizontal disparities. Therefore, the disparities of orientations and sizes, produced by the deformations, might be the more reliable indicators of stereoscopic tilt than the horizontal disparities.