Optical illusions

We went on a field trip to the museum a couple of weeks ago, and the exhibit topic was the brain. The brain needs us as much as we need it, which is a good thing because we wouldn't be ourselves without it! Optical illusions occur when "the information gathered by the eye is processed by the brain to give a percept that does not tally with a physical measurement of the stimulus source." (don't worry if you didn't get that, I barely understand it myself) : P


Here are a couple - um, three from my Aunt's email:

Focusing on the dot, move your head toward the screen, then back.

"To test this, stare at one spot for a couple seconds and everything will stop moving. Or look at the black center of each circle and it will stop moving. But move your eyes to the next black center and the previous will move after you take your eyes away from it.... ??

This one won't really work here...

Confusing....but thank God for brains!