Caption

Ouchi illusion. The central circular area of perpendicularly orientated bars appears to move and float compared to the surrounding pattern. The effect is particularly marked when the observer moves relative to the image. It is thought that the circular contour leads to ambiguity as to where the vertical bars terminate, and hence to ambiguity as to its own position. The brain therefore fails to integrate the whole image into a cohesive whole and so our eye movements cause apparent motion.