Abstract
Binocular rivalry is a phenomenon where two incompatible images are simultaneously presented, one to each eye, and elicit perceptual alternations between image dominance and suppression. Remarkably, binocular rivalry accommodates interocular grouping so that if portions of two globally coherent images are shown to each eye, subjects still perceive the global pattern far more often than would be expected by chance. In this study, we recorded the subject's perceptual reports (N=48) and MEG brain activity (N=30) while viewing classic rivalry (BR) or rivalry with interocular grouping (IOG). This was compared to conditions with increasing grouping demands; stimuli were divided into 2, 4, or 6 complementary patches shown to each eye. In all cases, participants reported their frequency and durations of dominant or mixed percepts, and stimuli consisted of flickering red or green orthogonal gratings at 5 or 6.7Hz, respectively. This allowed for analysis of tagged fundamental and intermodulation frequencies in the SSVEP with MEG. During BR, subjects perceived one of the two coherent images ~75% of the time, while for IOG, the coherent global percepts were seen at least 40% of the time. Compared to BR, IOG produced weaker MEG power at the fundamental frequencies in early visual cortex. However, IOG produced greater MEG signal beyond early visual cortex. Behavioral data demonstrates that grouping across the vertical image meridian is slightly more robust than across horizontal meridian, and this is supported by differences in MEG topography. Specifically, topography for vertical meridian IOG more closely resembles that obtained for BR. The reduced power for IOG in V1/V2 might be expected from less time spent perceiving/attending a coherent image, but patterns of intermodulation power suggest enhanced binocular integration, consistent with prior evidence from fMRI. We interpret this data with regard to collinearity and the balance of excitation/inhibition between early and later visual areas.