Abstract
Background and Goal. In binocular rivalry, two different visual stimuli are projected to corresponding retinal areas of the two eyes. Rather than fusing the two images into a coherent percept, observers usually report that the images alternate at a random rate, with one image dominant and the other suppressed. Here we used a binocular rivalry flash suppression paradigm in which monocular presentation of one stimulus results in suppression of that image when it is subsequently paired with a second stimulus. We investigated whether suppressed visual motion information affects perceptual performance and oculomotor behavior similarly.
Method. Stimuli were two large (6.7°) Gabor patterns that moved in orthogonal directions at 5°/s. The luminance contrast of the dominant stimulus was constant (10%), the suppressed stimulus varied in contrast (5 to 50%). Observers reported perceived motion direction at the end of each trial, and eye movements were recorded.
Results. While perceptual judgments exclusively followed the direction of the dominant stimulus, reflexive eye movements reflected the vector average of dominant and suppressed image motion. These findings were confirmed in two control experiments with smaller (1.6°) and faster (10°/s) stimuli. As luminance contrast of the suppressed stimulus increased, eye movements were biased in the direction of the suppressed stimulus.
Conclusion. These results show that reflexive eye movements can be used as a sensitive measure of the depth of suppression, as variations in depth of suppression by manipulations in stimulus weight were reflected in the eye movement response. Our findings imply that perception and action are differentially affected by suppressed visual information. While the action route is susceptible to suppressed visual information and simply averages all available information, the perception route is more resilient to suppressed visual information.
German Research Foundation DFG SP 1172/1-1 to M.S., NIH R01 EY016200-01A2 to M.C.