Binocular rivalry and surface-boundary processing.

Theoretical and empirical studies show that the visual system relies on boundary contours and surface features (e.g. textures) to represent 3-D surfaces. When the surface to be represented has little texture information, or has a periodic texture pattern (grating), the boundary contour information assumes a larger weight in representing the surface. Adopting the premise that the mechanisms of 3-D surface representation also determine binocular rivalry perception, the current paper focuses on whether boundary contours have a similar role in binocular rivalry. In experiment 1, we tested the prediction that the visual system prefers selecting an image/figure defined by boundary contours for rivalry dominance. We designed a binocular rivalry stimulus wherein one half-image has a boundary contour defined by a grating disk on a background with an orthogonal grating orientation. The other half-image consists solely of the (same orientation) grating background without the grating disk, ie no boundary contour. Confirming our prediction, the predominance for the half-image with the grating disk is approximately 90%, despite the fact that the grating disk corresponds to an area with orthogonal grating in the fellow eye. The advantage of the grating disk is dramatically reduced to about 50% predominance when a boundary contour is added to the background-only half-image at the location corresponding to the grating disk. We attribute this reduced advantage to the formation of a corresponding binocular boundary contour. In experiment 2 the grating background was substituted by a random-dot background in a similar stimulus design. We found that the perceptual salience of the corresponding binocular boundary contours extracted by the interocular matching process is an important factor in determining the dynamics of binocular rivalry. Experiment 3 showed that vertical lines with uneven thickness and spacing as the background reduce the contribution of the monocular boundary contour of the grating disk in binocular rivalry, possibly through the formation of binocular boundary contours between the local edges (vertical components) of the vertical lines and the corresponding grating disk.