Thanks to GeekPress for the pointer.

Well, it is fun and interesting, but 1 and 3 aren't really "illusions" in the sense that the brain is giving you wrong information. They play off the fact that we (correctly) try to compensate for light and shadow conditions in order to identify objects. In illusion #1, there is clearly a representation of a shadow, and if the shadow was removed the two squares would be very different in color.

This is no more an illusion than seeing a drawing of something circular (e.g. a cylinder) in perspective, and then having someone hold up an elliptical template to the 2D representation to "prove" that the end is really elliptical.
8.5.2005 1:50pm

Wow. Most excellent rod-and-cone abuse.

For those of you who go (look after reading this), disregard the "Instructions" button. It has no effect.

8.5.2005 2:02pm

Crud. Preview is your friend. The parenthesis in my prev comment was misplaced. I meant to say something more like "For those of you who have not yet gone to look, if you do so, disregard the "Instructions" button, for it has no effect."
8.5.2005 2:06pm
actually, no, the Instructions button has an effect -- it takes you back to the start page. If you press it while on the start page, it has no effect.
8.5.2005 2:09pm
Okay, I'm feeling stupid here and maybe I'm missing something; but, the third example, which is supposedly so "amazing," doesn't work when I view it. Both cross pieces that I see are the same color. They're both gray and look no more or less alike when I use the template than when I don't. Is the joke on me or do my eyes function differently from most people? (I ask this with true curiousity as we are currently dealing with the possibility that my infant son is seriously vision impaired due to a rod/cone defect.)
8.10.2005 4:51am