Barberpole illusion



The barberpole illusion is a visual illusion that reveals biases in the processing of visual motion in the human brain. When a diagonally-striped pole is rotated around its longer axis, so that the stripes are moving in the direction of the pole's shorter axis, it nonetheless appears the stripes are moving in the direction of its longer axis. Motion perception is biased in the direction of the longer axis. If the pole is reduced to a circle, the bias is removed and the true motion of the contour is obvious.