In binocular rivalry, incompatible monocular images presented to each of the two eyes causes the perception to alternate: one monocular stimulus dominates visual perception and then the other stimulus dominates, with a perceptual switch occurring every few seconds. Although it has been 170 years since this phenomenon was first systematic investigated, and a large number of studies have been performed, the neural mechanism of binocular rivalry is still unclear. The conclusions of some studies are even contradictory to each other. Vigorous debate about binocular rivalry has
concentrated on three main issues: Where does binocular rivalry happen? What types of visual representations compete? And, what mediates the competition?
Area 18 of the cat visual cortex receives projection from the LGN and parallel projection from area 17. The neurons in area 18 receive monocular visual input, and play a role in binocular integration. Here we performed voltage sensitive dye (VSD) optical imaging in area 18 of anesthetized cat to examine the mechanism of binocular rivalry. The results show that if conflicting stimuli with proper interval between their onset times were presented to the each of the two eyes, the cortical response to the later stimulus is suppressed by the response to the earlier stimulus. Furthermore, the pattern of neural activity seems to be stable when the rivalrous stimuli are presented intermittently, which is known to induce stable perception in human. This result suggests that the neuronal activity is consistent with perception and the binocular competition has begun in area 18.