Visual Perception...

...or, things that Don finds cool but doesn't feel like actually writing about.

This is convenient, because this guy Stuart Anstis, a professor at UCSD, has described things in detail. All you have to do is click the links and observe the cool optical illusions.

The term 'Optical Illusion' may be a bit of a misnomer here. This isn't a silly "do you see the young woman or the old woman?" or "do you see two faces or a candle-holder?" illusion, although those are very informative in the right context. This is actually a collection of images or movies that reveal how the neural pathways from the eye to the brain translate vision into perception.

Your rods and cones react to light. Each of them sends off a neural impulse when excited by a photon. The process by which each of these gazillions of impulses is encoded into one recognizable image is not at all trivial. In fact, the experiments that have been conducted to explore these hidden layers of cognition have only begun to reveal the truly beautiful mechanisms of the mind. Just enjoy the links.

http://psy.ucsd.edu/~sanstis/motion.html
http://psy.ucsd.edu/~sanstis/Plaid.html
http://psy.ucsd.edu/~sanstis/Foot.html
http://psy.ucsd.edu/~sanstis/SARevMotion.html
http://psy.ucsd.edu/~sanstis/Ring.html