Vertical disparity nulling in random-dot stereograms

Vertical alignment of monocularly visible structures has profound influence on a binocular system's ability to fuse high spatial frequencies of a random-dot stereogram. We show that monocular objects "capture" the vertical alignment: often less than 5% of the total stereogram area determines the state of the vertical alignment and can prevent fusion of the fine scale detail. This suggests that the human binocular system uses a heuristic in which, when monocularly salient information is available, stereomatching is attempted only at vertical alignment settings determined by the monocular structures.