Adaptation lengthens stimulus suppression time during binocular rivalry

Binocular rivalry refers to the perceptual alternations experienced while viewing dichoptic stimuli. Here we investigated the effect of adaptation on the perceptual alternations during binocular rivalry. Subjects (n=5) reported their percepts during 15 seconds of binocular rivalry after 20 seconds of binocular adaptation to one of the two stimuli (subtending 2.5 degrees of visual angle). The control task consisted of binocular rivalry without the adaptation phase. As predicted, the dominance phase of the adapted stimulus did not significantly differ from the dominance phase during the control task. However, suppression of the adapted stimulus, as measured by the dominance phase of the non-adapted stimulus, lasted 22-37 longer than that of control trials. To determine the functional level at which these adaptation effects occur, subjects repeated the experiment with composite images. The original two stimuli (including objects and backgrounds), were split on the vertical meridian, and one half was swapped, such that perception of either original object could only be obtained by fusing the appropriate halves of the dichoptically presented stimuli. Binocular adaptation of the intact object would adapt half of the stimulus presented to each eye. If adaptation effects are exclusively low-level, we would have expected the length of dominance for both objects to not significantly differ from one another, but both would be longer than in binocular rivalry alone, since the adapted stimulus was equally divided between the two composites. Conversely, if adaptation occurs at higher levels capable of integrating the halves of the objects from each eye, the expected results would be similar to that of the first experiment. Consistent with our previous results, dominance phases of the adapted stimulus did not change, but the time of suppression for the adapted object was significantly longer for all subjects (21-40). Results from both experiments suggest adaptation functionally ‘weakens’ the stimulus, expressed as an increase in the dominance phase of the competing stimulus. Moreover, adaptation led to binocular, object-driven effects suggesting rivalry can be influenced by higher levels of visual processing