Stereoscopic depth perception and vertical disparity: neural mechanisms

The additivity assumption relates to the various stereo-disparity components in the vertical and horizontal meridians, each of which is assumed to be independent of the other, with the total disparity in each dimension being the linear sum of the separate components. Information about the position of the eyes provided by the corollary discharge leads to compensatory changes in the lateral geniculate nuclei whereby the angle of gaze disparity component at retinal level is offset by equal and opposite changes at geniculate level. These geniculate changes concern only eye position. Changes in the retinal images such as those produced by lenses (i.e. induced effect) are passed on to the cortex without modification at the geniculate level. Discrimination of the local depth disparity component can be achieved by subtracting the local vertical eccentricity component from the total horizontal disparity.