Illusory contours and stereo depth

A theory for illusory contours, which fill gaps in certain figures, is proposed and subjected to an experimental test. We suggest that nearer masking objects are perceptually postulated to “account” for gaps when these are unlikely. The experiment shows that when stereoscopic depth information incompatible with this “perceptual hypothesis” is presented, the illusory contours are reduced in intensity or disappear.