Ten experiments were performed with computer-generated stereo images devoid of familiarity cues to investigate the role of contours in binocular depth perception. Contours were defined as the local maxima of brightness gradients in the monocular fields. In some of the experiments one or both of the stereo fields consisted of outlines drawn at the contours of the original fields. Primary attention was given to sensitivity to position of corresponding contours and outlines. The results indicate that in the absence of drawn outlines or if both stereo images are outlined, stereopsis is insensitive to relative position. On the other hand, if only one of the stereo images is outlined, position is critical. Whenever stereopsis is obtained, a uniform expansion of one image by 10% preserves stereopsis. It is shown that stereopsis of complemented simple outlines (similar to the stimuli used in Helmholtz’s classical experiment) gets increasingly more difficult as the spatial density of outlines is raised.
BELA JULESZ, "Stereopsis and Binocular Rivalry of Contours," J. Opt. Soc. Am. 53, 994-998 (1963)