Distortion of apparent shape of an object immediately before saccade.

'Perisaccadic mislocalization' is an illusion in which a stimulus presented briefly near the time of saccade onset is mislocalized. The amount of mislocalization depends on the stimulus location and the stimulus onset time relative to saccade onset. It is unclear whether perisaccadic mislocalization distorts the shape perception of a single object. To investigate this problem, we asked participants to report whether the apparent shape of a triangle presented for 10 ms before saccade was slanted in the same direction or the opposite direction as the saccade. The results showed that the apparent shape of the triangle was distorted in the direction opposite to the saccade. We compared this apparent distortion with the mislocalization of a perisaccadic vertical bar, and found that the time-course and direction of the distortion were similar, although the amount of distortion was smaller for the triangle. A hypothetical explanation for these results based on the forward/inverse optics model was discussed.