Illusory contours

Illusory contours or subjective contours are a form of visual illusion where contours are perceived without a luminance or color change across the contour. Friedrich Schumann discovered illusory contours.



A classic example of illusory contours is the Kanizsa triangle. This figure comprises three black circles with equal wedges cut out of them facing the center point and three black angles on a white background. But many observers see a white triangle on top of three black disks and an outline triangle. The white triangle appears brighter than the white background and shows a contour even in regions where there is no luminance change in the image.

The Ehrenstein illusion is another common form of illusory contours.

It is thought that early visual cortical regions such as V2 are responsible for forming illusory contours.