A criticism of the diffraction theory of some geometrical illusions

Chung Chiang (1968) invoked diffraction in the eye to explain Poggendorff’s illusion and extended the discussion to account for other geometrical illusions produced by intersecting lines. But diffraction in the eye cannot account for the displacement and rotation of lines assumed by Chung to produce Poggendorff’s illusion. And even if displacement and rotation do occur, the theory does not account for all illusions of the type considered. I am grateful to R. H. Day and M. Coltheart for critically reading a draft of this paper.