Neural correlates of adaptation within an episode of binocular-rivalry suppression

Binocular rivalry occurs when an observer looks at two different monocular images. One of the images is alternately suppressed, invisible, while the other is dominant, visible. Models of binocular rivalry hold adaptation responsible for these changes in visual consciousness. Alais et al. (2010, Current Biology) showed psychophysically that depth of rivalry suppression declines within an episode of suppression, consistent with the effects of adaptation. Our aim was to find a neural marker for this decline in suppression depth. We used electroencephalography (EEG) to search for this neural marker. We induced binocular rivalry with dichoptically orthogonal sine-wave gratings. Participants pressed keys to record their perception of orientation. On each trial, we changed one of the gratings to be the same as the other, either to the currently suppressed or to the currently dominant stimulus. On different trials, we made the change at an individually adjusted short time (about 200 ms), medium time (about 700 ms), or long time (about 1200 ms) after the participant signalled a new percept. We found the earliest neural correlate of suppression about 100 ms after the stimulus change, with invisible changes yielding a smaller positive deflection (P1) than visible changes. The P1 difference was pronounced for the short and medium times, and almost abolished for the long time. The decline from short and medium times to the long time is consistent with the expected reduction in suppression depth with time in the suppression interval, and consistent with the psychophysical results. We conclude that we have shown a neural correlate of the adaptation leading to changes in visibility during binocular rivalry