Seeing isn't necessarily the direct perception of reality. Actually, our brains are constantly interpreting and giving structure to the visual input from our eyes. Our eyes communicate with our brains in mysterious ways-all the more evident with these optical illusions:
Beans Beans Beans!
Stare at the image for a bit, then look away. The beans will magically start moving!
Look at the red dots, the wheel appears to move in one direction. Now look at the yellow dots, and the wheel will appear to move in the opposite direction!
Stare into the centre of the circle. You should see pulsating waves moving outward from the centre. If you don't see this, see a doctor!