Clashing interpretations of Ponzo’s illusion: reconsideration of assimilation versus tilt-constancy theories1

Abstract

Prinzmetal criticized the explanation provided by Pressey's assimilation theory of Ponzo's illusion on the basis of an experiment designed to test the theory However, it is demonstrated that their test was faulty because it did not take into account the manner in which a gap between fins and shaft alters Müller-Lyer's illusion. Additional criticisms are shown to be unfounded because implications from assimilation theory were not properly derived. Tilt-constancy theory itself was shown to be inadequate because observations about Holding's illusion, Morinaga's paradox, and a modified Ponzo illusion all contradict the theory.