An upper limit to the binocular combination of stimuli.

It is important to know the spatial extent over which the binocular visual system searches for "matches" or image correspondence. Most models of stereopsis define fixed neighbourhoods in one monocular image in which a search is conducted for a match to some element in the other image. We were unable to experimentally determine fixed values for the extent of these neighbourhoods. We were, however, able to derive a simple rule that predicts performance on a binocular matching task over a large spatio-temporal region, and from which we can calculate the efficiency of our observers. We conclude that the human visual system does not use neighbourhoods of a single, fixed extent to perform binocular matching in a single region of the visual field, but uses more flexible scheme that allows it to function well under a broad range of stimulus conditions.