A visual illusion of a triangle without a corresponding retinal image, induced by three dark Pac-Man icons at the corners of an imaginary triangle, oriented to give the impression that they are discs with segments occluded by the vertices of the triangle (see illustration). The illusory contour arises from processing that occurs in Area V2 of the visual cortex of information sent there from the primary visual cortex. The other major example of form perception without a retinal image is anorthoscopic vision. Compare Ehrenstein's brightness illusion, random-dot stereogram. [Named after the Italian psychologist Gaetano Kanizsa (1913–93), born in Trieste when it was part of the Austro-Hungarian Empire, who discovered it in 1971]
Kanizsa triangle. A figure with illusory contours and no corresponding retinal image.