Conditions required for binocular rivalry suppression.

When the two eyes are presented with incompatible stimuli, the two monocular stimuli are seen alternately in a never-ending cycle. It is now widely accepted that the neural processes underlying this phenomenon, binocular rivalry, are distributed across a number of cortical stages. It is not clear, however, where binocular rivalry is initiated. We performed two experiments whose aim was to clarify this issue. In the first experiment, rivalry was induced, and brief test stimuli were delivered to an eye while its inducing stimulus was either dominant or suppressed. Sensitivity to a test stimulus with features similar to those of the suppressed inducing stimulus was reduced only when the test was presented to the eye whose inducing stimulus was suppressed. This indicates that suppression of a monocular channel is a prerequisite for binocular rivalry suppression. The second experiment showed that to induce rivalry, local interocular stimulus incompatibilities were necessary and that conflicting global percepts were not sufficient. These results suggest that low-level visual processes are required for the initiation of binocular rivalry.