Spatial frequency tuning of the Ouchi illusion and its dependence on stimulus size.

This study investigated the effects of the stimulus size on the spatial frequency tuning of the Ouchi illusion, which is an illusory sliding motion perceived in a checkerboard pattern of rectangular elements that is surrounded by a checkerboard pattern of orthogonally oriented elements. Two experiments were conducted to measure the perceived strength of illusion. The optimal size of the inner pattern increased proportionally with check size. In contrast, the optimal check size increased with the size of the inner pattern but not proportionally, and the range of increase was relatively small. The optimal fundamental spatial frequency was lower for a larger stimulus both for checkerboard patterns and simpler sinusoidal grating patterns, but there were differences in the tuning curves for the two types of stimuli. These results support the idea that two processes underlie the Ouchi illusion; one computes the local motion direction, and the other integrates motion signals across space for surface segmentation. For the checkerboard and grating stimuli, the former process may be different while the latter can be shared.