Stereopsis and binocular rivalry.

Stereopsis and binocular rivalry appear to be incompatible. Rivalry involves suppression of input from one eye at each location in space and time, whereas Stereopsis requires the combination of information from both eyes to yield a sensation of depth. This article presents a theory of the relationship of these phenomena. Evidence from previous work and from experiments reported here shows that (a) the pathways mediating Stereopsis are separable from those mediating rivalry; (b) Stereopsis and rivalry can coexist at the same point in space and time; (c) rivalry occurs inevitably, whenever visual stimuli are present, even if identical stimuli are presented to both eyes; and (d) Stereopsis can be disrupted without disrupting rivalry and vice versa (termed double dissociation). On the basis of the evidence, it is proposed that rivalry and Stereopsis involve independent and parallel pathways through the early stages of visual processing and that binocular perception is a simple combination (probably a weighted average) of the output of the pathways mediating Stereopsis and rivalry.