Abstract
When two dissimilar stimuli are presented dichoptically, the percept generally alternates between the two monocular stimuli; a phenomenon known as binocular rivalry. The dominance of a specific percept during rivalry can be affected by a surrounding stimulus. For example, if two discs containing bars with orthogonal orientations are both surrounded by an annulus containing bars with the same orientation as one of the two discs, the disc containing the bars orthogonal to the surround is more dominant (Fukuda & Blake, 1992). Here, we investigate whether this preference for a stimulus deviant from its surround can also be observed for moving stimuli.
Stimuli: Two discs containing vertical sine-wave gratings, always moving horizontally in opposite direction, were presented dichoptically at the center of fixation. The discs could each be surrounded by an annulus containing a vertical sine-wave grating moving in the same direction as one of the two discs. The annulus was either presented to one eye [one-eye condition] or both eyes [two-eyes condition]. In the two-eyes condition, the annuli moved in the same direction. In the one-eye condition, the grating in the annulus moved in the same direction as the grating in the disc in the same eye, or in the same direction as the grating in the disc presented to the other eye. Observers had to continuously indicate the perceived direction of motion in the center disc.
Results: For both conditions, the disc containing the grating with a direction of motion opposite to the surround was more dominant. Most interestingly, for the one-eye condition, the disc containing the grating moving in the direction opposite to the motion in the annulus was more dominant, irrespective of its positioning (same or different eye as compared to the annulus). Thus, also during binocular rivalry of moving stimuli, the grating in the disc moving in the deviant direction, as compared to the motion direction in the annuli, is preferred.