2-DIMENSIONAL MATCHES FROM ONE-DIMENSIONAL STIMULUS COMPONENTS IN HUMAN STEREOPSIS

Three-dimensional visual scenes project onto the retina of the eye as two-dimensional images. The third dimension, depth, is projected as su btle differences between left and right retinal images. As early as th e 1830s, stereoscopic depth perception was shown to depend on horizont al disparities between these images(1) To detect disparity, the visual system must match corresponding parts of the two retinal images. To i dentify the stimulus elements used in stereo matching, I applied a dis parity-adaptation technique to visual patterns whose one-dimensional c omponents and two-dimensional features have very different disparities . Surprisingly, the adaptors that are effective in altering depth perc eption appear widely separated in depth from the patterns they adapt. I conclude that stereo matching occurs in all directions of two-dimens ional space and that one-dimensional components are the stimulus primi tives, the fundamental elements of stereo matching. This is a reversal of the classical view of stereo correspondence as a one-dimensional ( horizontal) matching of monocular two-dimensional features(2-4).