| COLOR REVERSAL
shows the interesting effect that occurs when color receptors in
the eye become fatigued. The opening in a rotating black wheel reveals
a picture of a red tree with a green background. If the wheel spins
in one direction, the picture is followed by a white card. In the
other direction, the picture is followed by black. If white follows
the picture quickly, the user sees a green afterimage as the color
receptors in the eye become fatigued (white minus red equals green).
If the black follows the tree, the afterimage remains red.