Perception of multiple transparent planes in stereo vision

INFORMATION about the distances of objects that we see can be obtained from the disparity in position of their images in our two eyes. This process entails solving the problem of stereo-matching, which involves the determination of which points in the two images correspond to the same object. This is particularly problematic when features in the visual field are repeated, allowing more than one possible solution to the stereo-matching problem. Here I describe a situation in which a repetition of a random dot pattern leads to the perception of multiple transparent planes under some conditions, and of a single opaque plane under other conditions. This result shows that stereo-matching is not necessarily unique-a given point of the image in one eye may be matched simultaneously to more than one point in the other eye, each match defining a different depth plane. Current stereo-matching algorithms in computer vision do not account for these observations.