Abstract
In binocular rivalry, conflicting visual inputs result in perceptual alternations of the two inputs. Levelt (1968) demonstrated that increasing the contrast of one eye's stimulus does not affect the mean duration of perceptual dominance of that stimulus, but instead decreases the mean duration of perceptual dominance of the stimulus presented to the unmanipulated eye. Stimuli introduced by Diaz-Caneja (1928) have been used to study perceptual selection at different levels of the visual processing hierarchy. Specifically, a horseshoe-shaped stimulus facing either left or right is presented to one eye, and a horseshoe stimulus facing in the opposite direction is presented to the other eye. These stimuli result in four distinct percepts: left-facing horseshoe, right-facing horseshoe, concentric circles, and horizontal lines. The horseshoe percepts correspond to the monocular images, while perception of horizontal lines or concentric circles requires integration of information from both eyes and therefore reflects perceptual dominance of binocular stimulus representations. In this study, we manipulated the contrast of either the monocular horseshoe stimuli or the portions of each stimulus that group to form percepts of concentric circles or horizontal lines. Our results show that for Diaz-Caneja stimuli, increasing the contrast of a stimulus increases the mean perceptual dominance duration of that stimulus, in contrast with the classic Levelt finding. In addition, increasing the contrast of a monocular stimulus increases the probability of perceptual selection of that stimulus, but increasing the contrast of portions of the stimuli that form an interocularly grouped percept does not change the probability of perceptual selection of that percept. These results suggest that selection processes in binocular rivalry are distinct from those that underlie the maintenance of perceptual dominance and that the strength of inhibition from the suppressed eye is not the only determinant of perceptual dominance maintenance.
National Science Foundation Graduate Research Fellowship.