Anisotropies of linear and curvilinear completions at the blind spot.

Previous studies have shown anisotropies of perceptual completion of the line at the blind spot. The present study examined anisotropies of collinear and noncollinear completions at the blind spot. A physically aligned or misaligned pair of horizontal or vertical line segments was presented on opposite sides of the blind spot. Observers reported the appearance of the line segments. In Experiment 1, the range of noncollinear completion in the vertical line segments was significantly larger than that in the horizontal line segments, whereas an anisotropy of the range of collinear completion was not observed. In Experiment 2, linear and curvilinear completions predominantly occurred in the horizontal and vertical line segments, respectively. In Experiment 3, the tolerance of collinear completion was not significantly larger than vernier acuity. These results suggest that linear and curvilinear completions at the blind spot have different anisotropic tendencies. These different anisotropic processes might bring about anisotropies of perceptual completion of the line at the blind spot.