The illusions and Ganz's theory of contour displacements.

Ganz's theory of contour displacements is summarized, and it is pointed out that its success or failure in explaining the illusions depends upon establishing the identity of the illusions and figural after-effects. Evidence is quoted which casts doubt on Ganz's claims for such an identity. Moreover, it is shown that predictions from Ganz's theory about some common illusions do not correspond with observed phenomena.