Right Side Up; 105 Mind-Bending Illusions; Special Editions; by Vilayanur S. Ramachandran and Diane Rogers-Ramachandran; 4 Page(s)

The lens in your eye casts an upside-down image on your retina, but you see the world upright. Although people often believe that an upside-down image in the eyeball gets rotated somewhere in the brain to make it look right side up, that idea is a fallacy. No such rotation occurs, because there is no replica of the retinal image in the brain-only a pattern of firing of nerve impulses that encodes the image in such a way that it is perceived correctly; the brain does not rotate the nerve impulses.

Even leaving aside this common pitfall, the matter of seeing things upright is vastly more complex than you might imagine, a fact that was first pointed out clearly in the 1970s by perception researcher Irvin Rock, then at Rutgers University.