The ponzo illusion: inadequacy of apparent depth explanations.

Abstract

Os viewing the Ponzo figure reported a series of sudden changes in its phenomenal organization and orientation. In none of these was the vertical line nearer the vertex of the figure reported to be smaller than the vertical line nearer the open end, i.e., the illusion occurred with all percepts except a rare one of a flat stimulus. In two of the most frequent and persistent percepts, the illusion could be explained on the basis of apparent size-apparent distance relationship among the elements. This was also the case with Gregory's theory of misapplied size-constancy scaling. However, with other percepts neither of these explanations was tenable.