Perceptual filling-in of a line segment presented on only one side of the blind spot.

Two experiments examined whether filling-in occurred at the blind spot when a line segment was presented on only one side of the blind spot. We used static and dynamic stimuli: a static test line segment and a pair of probe line segments were presented in Experiment 1 and a moving test line segment was presented in Experiment 2. We compared the probability that the proximal end was perceived to be on the blind spot side when the test line segment came into contact with the blind spot (blind spot condition) with that when the test line segment was outside the blind spot (control condition). The results of the two experiments showed that the proximal end was perceived to be more on the blind spot side in the blind spot condition than in the control condition. Notably, when a dynamic stimulus was presented below the blind spot, the mean amount of filling-in reached 2.84 degrees. Therefore, filling-in occurred at the blind spot even when a line segment was presented on only one side of the blind spot.