Surface boundary contour strengthens image dominance in binocular competition

We used a binocular rivalry stimulus with one half-image having a vertical grating disk surrounded by horizontal grating, and the other half-image having a horizontal grating disk with a variable spatial phase relative to the surrounding horizontal grating. We found that increasing the phase-shift of the horizontal grating disk, which strengthens the boundary contour, progressively increases its predominance. But the predominance is little affected when a constant gray ring (boundary contour) is added onto the rim of the incrementally phase-shifted horizontal grating. This suggests the influence of boundary contour supersede that of the center-surround-interaction caused by the phase-shift.