Differentiating the contributions of surface feature and boundary contour strengths in binocular rivalry

摘要

Binocular rivalry (BR) is typically stimulated with a pair of grating half-images with orthogonal orientations. These half-images can be characterized by their surface boundary contour (outline) and surface feature (interior texture/grating) properties. We have shown when the interior surface feature (grating contrast) is constant, BR predominance of seeing a grating half-image increases with its boundary contour strength (Ooi & He, Perception 2006; Xu et al, Vision Research 2009). Here, we revealed the sole contribution of surface feature to BR. We used 1-deg grating discs (5 cpd, 35 cd/m2). One disc (e.g., horizontal) was fixed at 30% contrast while the other (vertical) assumed one of three contrast levels (30, 50, 85%). Two conditions were tested. (1) Disc-only condition: The grating discs were displayed against a gray background so changing the grating disc contrast varied both its boundary contour and surface feature strengths. (2) Disc-plus-background condition: The grating discs were displayed against a 135 deg grating background. The grating background contrast in one half-image was the same as the grating disc contrast in the fellow eye. This ensured that changing the contrast of one grating disc varied only the surface feature strength of that grating disc, while equalizing the boundary contour strength of the right and left half-images' grating discs. Observers tracked their BR percepts of the grating discs for 30 sec in each trial. We found increasing the contrast of one grating disc increased its predominance and dominance duration in the disc-plus-background condition, indicating the sole impact of surface feature strength. The increases were, however, smaller than that in the disc-only condition where both boundary contour and surface feature strengths contributed to BR. Thus, the present findings along with our previous results reveal both the surface boundary contour and surface feature strengths are separate factors influencing BR.