The role of retinal correspondence in stereoscopic matching.

On brief viewing, stereo matching of a regularly-spaced horizontal row of points is determined by the disparity of the points at the edges. Stereo matches on corresponding retinal loci are initially overridden in favor of matches located on or near the disparity plane of the edge points. Edge-based matching is observed when the inter-point spacing is as large as 15-30 min arc for crossed disparities, and as large as 1 deg for uncrossed disparities. Edge points located at a lateral distance more than 2.5 deg away from the center of the row can still determine the initial stereo matching of the center. Given longer viewing time, vergence usually changes from the fixation plane towards the initially-perceived depth plane associated with the edges. However, if the eyes are held tightly converged in the fixation plane, the edge-based matches will gradually yield to matches in the fixation plane. This shift from edge-based matching to a match determined by retinal correspondence takes 1-4 sec if the inter-point spacing is large (10-30 min arc). For smaller inter-point spacings, the edge-based matches are very stable, and a shift in depth is seldom discernible.