Here's a video of a pretty powerful optical illusion of a checkerboard. Non-random placement of the white dots creates the illusion of a bulge. When the dots are removed, the illusion disappears. Several other similar optical illusions can be accessed via this video and they all are pretty troubling in that you can't make you brain see what is actually there. Why does TPP look at such things on a Monday morning before the second cup of coffee, as if that would matter? In other instances of optical illusions, TPP has noticed that he often has a strong reaction to such illusions and wonders if that is in some way related to all his years of looking through microscopes? HT to Mano Singham's blog; he's a physicist.