Barberpole illusion
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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 vertical axis so that the stripes are moving in the direction of the pole's horizontal axis, it appears the stripes are moving in the direction of its vertical axis.
[edit] Explanation
This illusion occurs because the perception of motion is biased in the direction of the longer (in this case, vertical) axis. Rather than being perceived as rotating, the viewer will have the illusion of ascending or descending stripes (depending upon the direction of spin). (See Example one)
If the pole is reduced to a circle, the bias is removed and the true motion of the contour is obvious. (See Example two)
[edit] See also
- Barber's pole for the modern device exploiting this illusion
