What prior uniocular processing is necessary for stereopsis?

In order to induce stereoscopic depth, retinal images in the right and left eyes must differ. Our experiments demonstrate that these uniocular differences for simple three-line configurations at stereo-threshold cannot usually be distinguished one from the other. We confirm that depth values are associated with individual features by virtue of their disparity, rather than by a comparison of their image separations in the two eyes. In ordinary stereoacuity patterns, no prior identification of monocular relationships is needed to produce discriminable depth differences. For certain patterns, disparity of the positions of the averages of the targets' internal light distributions in the two eyes can substitute for disparity of pattern contours in stereoscopic depth discrimination.