Comparison of stimulus rivalry to binocular rivalry with functional magnetic resonance imaging.

When incompatible images are presented to each eye, a phenomenon known as binocular rivalry occurs in which the viewer's conscious visual perception alternates between the two images. In stimulus rivalry, similar perceptual alternations between rival images can occur even in the midst of fast image swapping between the eyes. Here, we used functional magnetic resonance imaging to directly compare brain activity underlying the two types of perceptual rivalry. Overall, we found that activity for binocular rivalry was always stronger and more widespread than that for stimulus rivalry-even more so during passive viewing conditions. In particular, the right superior parietal cortex and the right temporoparietal junction were prominently engaged for passive binocular rivalry. While both types of rivalry engaged higher tier visual regions such as the ventral temporal cortex during an active task, activity for stimulus rivalry was comparatively weak in early visual areas V1 to V3, presumably due to a weaker feed-forward signal due to both intraocular and interocular inhibition that may reduce effective contrast. In sum, only binocular rivalry produced perceptually vivid alternations, increased activation of the early visual cortex, and the coordinated engagement of dorsal stream regions, even when a task was not performed. These findings help characterize how stimulus rivalry fits within hierarchical models of binocular rivalry.