A method for investigating binocular rivalry in real time with the steady-state VEP

Under conditions in which the visual system cannot reconcile dissimilar images from the two eyes, perception typically alternates between the two half-images---a process known as binocular rivalry. We report a real-time, steady-state VEP method that is a sensitive detector of the continuous alternations in perceptual dominance across the eyes. This method works by labeling each half-image with a slightly different emporal frequency so that the record generated by each can be recovered from the EEG by spectrum analysis. In this way, one can track the "waxing " and "waning " of the VEP amplitudes for each eye simultaneously during spontaneous rivalry, permitting an analysis of the relative physiological dominance of each eye in real-time. Such alternations were clearly observed in the VEP amplitudes generated by each half-image during rivalry (the amplitudes for the two eyes correlated negatively). In contrast, VEP amplitudes for the two eyes varied either synchronously or randomly when the half-images were allowed to fuse. The instances of physiological dominance of each eye as evidenced by the VEP correlated well with the subjects ' report of perceptual dominance. This purely electrophysiological method appears to be suitable for measuring rivalry in non-verbal human or animal subjects, as it does not require active participation from them. © 1997 Elsevier Science Ltd. binocular rivalry steady-state VEP dichoptic viewin