EEG Decoding of Conscious versus Unconscious Representations during Binocular Rivalry

Theories of visual awareness often fall into two general categories, those assuming that awareness arises rapidly within visual cortex and those assuming that awareness arises more slowly as a result of interactions between visual cortex and frontoparietal regions. To test the plausibility of early theories of consciousness, we combined the temporal resolution of the EEG technique with multivariate pattern classification techniques to assess the latency at which decodable information about consciously perceived stimuli is enhanced relative to information about stimuli that are not consciously perceived. Competing red and green gratings were presented simultaneously to the two eyes, creating rivalry, and observers reported which one of the two colors was perceived on each trial. We then used the pattern of EEG over the scalp to decode the orientation of the grating that was perceived and the orientation of the grating that was suppressed by the rivalry and not perceived. This allowed us to determine when the content of the neural representations differed between the consciously perceived grating and the unconscious grating. Early theories predict that the difference between conscious and unconscious processing would occur within ∼200 msec of stimulus onset (e.g., at the time of the visual awareness negativity). We found that decoding accuracy was significantly greater for the consciously perceived orientation than for the unperceived orientation beginning 160 msec after stimulus onset, as predicted by theories that propose a rapid onset of visual awareness.