EYEBALLS provides a physical ilustration of the stereo rule with two giant eyeballs. Each giant eyeball has a cornea, a lens and a retina. Two mailboxes in front of the eyes have large rear-lit letters-- a red F and a green P. Images of the F and P appear on the back of the eyeballs. You can see how these images are upside down and different distances apart in each eye. The placement of the images on the retina is one of the clues the brain uses to determine depth. You can move the mailboxes and see the affect the placement of the images on the retinas.

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