Why Are Our Brains Fooled By Optical Illusions?

My mind is playing tricks on me!

Discover Magazine systematically dissects five fantastic optical illusions. The scientific explanations are logical:

"our brains are programmed to see the world in three dimensions instead of two"

...or...

"illusion arises when cells in the retina and the brain respond to certain wavelengths of light"

...or...

"your mind fits the drawing to a physical object that makes sense based on your experience." 

Patiently explore all five examples.

My favorite happens to be Shady Situation:

"The top and bottom planes of this shape seem to be distinct, separated by a thin band of shadow. In reality, both are the same absolute color.

Your brain perceives the gradients where the tiles meet as curves, and you surmise that light hits the large, flat surface of the top tile and fades to shadow at its curved bottom edge; for the bottom tile, the opposite holds. Automatically your mind fits the drawing to a physical object that makes sense based on your experience, altering your visual perception to match expectations."

And your favorite? Comment below, please.

• Previously, Get High Without Taking Drugs.
• Get Mind-Screwed: The Grand Illusion of the Year.