Occlusion, transparency, and stereopsis: a new explanation for stereo capture

Stereo capture occurs when a regular pattern of repeating elements with zero disparity is superimposed on a disparate subjective figure. The elements enclosed within the subjective contours, but not those outside them, are perceptually captured and pulled on the same depth plane of the disparate figure. The phenomenon has been interpreted as the result either of a spreading of disparity signals from the subjective figure or of the attribution of the depth of certain salient image features to the finer texture elements enclosed in them. We suggest here that, instead, the fact that stereo capture is limited to the texture elements lying within the boundaries of the subjective figure is simply due to ambiguous occlusion information at the monocular level. When the texture elements occlude the inducers of the subjective figure as well, the elements lying outside the boundaries of the subjective figure are also captured. We propose that stereo capture arises as the solution to a conflict between information provided by retinal disparity and occlusion, and show how this effect is related to other previously observed phenomena of conflicting cues to depth.