Spatial interaction in the domain of disparity signals in human stereoscopic vision.

When a few isolated features are viewed foveally, changes in the binocular disparity of one introduces apparent depth changes in others. For features a very few minutes of arc apart, the effect is equivalent to a pooling of their disparity signals, even though the features are seen distinctly as separate. When the distance between them is 4-6 minutes of arc or more, the effect is in the opposite direction: the features act as if they repelled each other in depth. Using a null method, it was possible to characterize this interaction effect numerically. There are some quantitative, but no qualitative, differences between observers, and in any one observer the disparity interaction between vertically separated targets is not necessarily the same as between horizontally separated ones. The disparity interaction effect is seen with presentations both of 50 ms and of 1 s duration. There is a very small temporal after-effect, seen when the extinction of inducing flanks is synchronous with test target onset.