Frontal theta EEG rhythms appeared during continuous attention to dominant eye reflect attention level during binocular rivalry

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Binocular rivalry and attention both involve selection of visual stimuli and suppression of unattended information. In this study, we explored whether the frontal midline theta electroencephalogram rhythm (Fm-theta)_which was thought to reflect focused voluntary attention, was related to suppression of information from the suppressed eye in binocular rivalry. When subjects were asked to play a computer game using the left eye, a gray screen image was presented to the right eye using a monocular head-mounted display (HMD). An alphabet letter was randomly flashed on the HMD and subjects were asked to report whether they saw it or identify it, while EEGs were recorded. During the game, half of the subjects displayed Fm-theta and a ratio of detected letters was significantly less than that of the other subjects (who didn't show Fm-theta). Of the Fm-theta positive subjects, Fm-theta disappeared when the letters were visible, but was sustained when the letters were not seen. Visual evoked potentials evoked by detected letters could not be evoked when letters were undetected, but P300-like deflection was observed in place of them. Above data suggest that attention level for the dominant image during Fm-theta appearance might be higher than that seen during Fm-theta, disappearance. We hypothesize that, in the Fm-theta positive subjects, there is greater receipt of information from the dominant eye during binocular rivalry, while there is stronger suppression to the receipt of information through the V1 area from the suppressed eye. Perceptive suppression on the extrageniculate system may be ineffective, even during concentrated attention.