Anisotropy of tolerance of perceptual completion at the blind spot

Three experiments examined anisotropies of tolerance of perceptual completion at the blind spot when a pair of line segments was presented on opposite sides of the blind spot. The tolerance of perceptual completion is defined as the maximum difference in a stimulus attribute between the line segments on opposite sides of the blind spot when perceptual completion of a line has occurred. The misalignment, orientation difference, and luminance difference between the line segments were used as the stimulus attributes in Experiments 1, 2, and 3, respectively. The results showed anisotropies of the tolerance of perceptual completion between horizontal and vertical configurations of the line segments. Vertical superiorities, which imply a greater extent of tolerance in the vertical configuration than that in the horizontal configuration, were observed for misalignment and orientation difference, while horizontal superiority, which implies a greater extent of tolerance in the horizontal configuration than that in the vertical configuration, was observed for luminance difference. We discussed possible origins of the anisotropy of the tolerance of perceptual completion at the blind spot.