Reversing ocular dominance and suppression in a single flash.

An observer views a long (1-2 sec) monocular stimulus. Following stimulus offset there is a dark interstimulus interval (ISI). After the ISI, brief test flashes are presented to both eyes simultaneously. For ISIs less than 100-200 msec, only the test flash contralateral to the stimulated eye is seen. The test flash in the ipsilateral eye is not seen. For ISIs of 200-1000 msec, the contralateral test flash is seen more clearly and completely than the ipsilateral flash (Experiments 1 and 2). The initial and ipsilateral test flash need not be spatially similar. The initial stimulus can be dim but must be longer than 150 msec (Experiment 3). Experiment 3 precludes forward masking or light adaptation as explanation. The effect is relatively independent of the length of the test flash (Experiment 4). The results can be explained in terms of the known properties of binocular rivalry and reinforce the hypothesis (Fox and Check, 1968) that rivalry acts nonselectively, independent of factors such as spatial frequency, luminance, or orientation.