Optical Illusions

Since photography is a visual medium (duh) and there is a lot of discussion here and elsewhere about subjective perceptions of sharpness, contrast, color, depth, and illusion of motion, I thought y'all might be interested in this site that contains one of the best collection and explainations of various types of optical illusions. Most are illustrated by animations and complete references to the psychology of perception that makes them work:

http://www.michaelbach.de/ot/index.html

There are a few that I seen already (but they are described better), but there are also some new ones that i have never seen before...