Junxian Rao¹ (), Chuan Hou¹; ¹Smith-Kettlewell Eye Research Institute

When incompatible images are presented to each eye at the exact spatial location, perception alternates between them as they compete for dominance, a phenomenon known as binocular rivalry. While previous studies suggest that the neural representations of the rival stimuli compete for visual awareness beyond the primary visual cortex (V1), the precise contributions of different brain regions in the visual hierarchy remain unclear. Here, we investigated the neural mechanisms underlying binocular rivalry by presenting a pair of orthogonal gratings tagged with different temporal frequencies (F1=7.5Hz, F2=6Hz) in each eye to normal vision observers. The participants indicated their perceptual experience (i.e., horizontal or vertical) by pressing one of the two buttons. Neural activity during binocular rivalry and monocular stimuli was recorded using fMRI source-localized 128-channel EEG to provide high spatial definition to the neurophysiological signals. We correlated neural responses from different brain regions with the perceptual reports to examine activity during the dominance and suppression phases. Our findings showed that extrastriate visual areas, including hV4, the middle temporal (MT) area, lateral occipital cortex (LOC), and higher-level cortical regions (e.g., frontal pole) exhibit more robust neural responses during binocular rivalry compared to V1. Notably, the frontal pole showed the highest neural response, indicating that cognitive cortical regions, such as frontal cortices, are involved in rivalry processing. Moreover, compared with the monocular stimuli, the magnitude of neural suppression increased from V1 to extrastriate visual areas (MT and LOC) and the frontal pole. Suppression was again highest in the frontal pole, suggesting that the cognitive cortices might mediate visual awareness during binocular rivalry. Our results support a three-tier model of binocular rivalry processing, with V1 at the first level, extrastriate areas at the second level, and the frontal region at the third level.

Acknowledgements: This research was supported by NIH grant R01EY035346 to C. H.