Optical illusions come in two flavors. The one shown on the left is a classical example of a “false” perception. It looks like the grey lines are curved, but they are actually perfectly horizontal. Even if we know that the lines are horizontal, we cannot force ourselves to see them this way. I find it somewhat of a miracle that reason is strong enough to tell that the eyes are lying, but still, however long you stare at the picture, you will never see it the right way. The brain cannot learn to see this picture.

The second flavor of optical illusions is shown on the right. This picture may either represent the face of a woman, or a saxophone player. Most people immediately see one of those, and it may take them some time to see the other. But once they see it, there is no way to “unsee” it. The brain has completely forgotten how it feels to not see it and cannot unlearn to see the picture.

Vision is not the only sense that can be fooled. As a matter of fact, what is so special about optical illusions is that we realize that something...