Characteristics of the filled-in surface at the blind spot.

Our visual system can restore information missing within the portion of the retinal image corresponding to the blind spot where the optic nerve exits the eye. Previous studies of the properties of filled-in surfaces at the blind spot have found similarities and dissimilarities between filled-in and real surfaces and have therefore not provided a consistent view of the characteristics of the filled-in surface. First, we investigated whether filling-in utilizes a contour integration mechanism. Gratings with collinear lines filled in the blind spot more effectively than those both with orthogonal lines and without any line, suggesting that collinear facilitation underlies the filling-in of the blind spot. Second, the dynamics of binocular rivalry was examined by comparing the dominance duration distributions of filled-in and real surfaces. The results indicated that the strength of the filled-in surface was attenuated compared to that of the real surface during rivalry. Lastly, we tested whether travelling waves of dominance in rivalry could occur at the blind spot. The travelling waves could propagate through a hole only at the blind spot, suggesting that the filled-in surface helps perceptual waves to travel across the blind spot. These results suggest that the filled-in surface shares a common mechanism via a horizontal connection but that it has weak strength to suppress the opposite eye during binocular viewing.