Abstract
A fundamental question in cognitive science is the relation between knowledge and perception: does our knowledge of the world influence the way we see it? To help answer this question, we used the Ebbinghaus illusion, in which a circle looks larger when surrounded by smaller circles than when surrounded by larger ones. Unlike circles, coins - such as quarters or dimes - have a fixed size, and we predicted that such knowledge of object constancy would weaken the perceptual illusion. A hundred observers reported the apparent size of a quarter when surrounded by dimes, and when surrounded by one-dollar coins. The apparent size of the quarter was compared to the apparent size of a circle when surrounded by small circles, and when surrounded by big circles. Consistent with our hypothesis, the illusion was weakened for coins. We interpret this result to suggest that visual perception is influenced by semantic knowledge, such as the knowledge of coins as objects of invariant size.