Interocular rivalry revealed in the human cortical blind-spot representation

To understand conscious vision, scientists must elucidate how the brain sel ects specific visual signals for awareness. When different monocular patter ns are presented to the two eyes, they rival for conscious expression such that only one monocular image is perceived at a time(1,2). Controversy surr ounds whether this binocular rivalry reflects neural competition among patt ern representations or monocular channels(3,4). Here we show that rivalry a rises from interocular competition, using functional magnetic resonance ima ging of activity in a monocular region of primary visual cortex correspondi ng to the blind spot. This cortical region greatly prefers stimulation of t he ipsilateral eye to that of the blind-spot eye. Subjects reported their d ominant percept while viewing rivalrous orthogonal gratings in the visual l ocation corresponding to the blind spot and its surround. As predicted by i nterocular rivalry, the monocular blind-spot representation was activated w hen the ipsilateral grating became perceptually dominant and suppressed whe n the blind-spot grating became dominant. These responses were as large as those observed during actual alternations between the gratings, indicating that rivalry may be fully resolved in monocular visual cortex. Our findings provide the first physiological evidence, to our knowledge, that interocul ar competition mediates binocular rivalry, and indicate that V1 may be impo rtant in the selection and expression of conscious visual information.