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The power of optical illusions

While looking for optical illusions to motivate my discussion of probability illusions I came across this illusion on Wikipedia (by Adrian Pingstone, based on the original created by Edward H. Adelson). In the picture below compare the squares A and B. As hard as it is to believe, both squares are exactly the same shade of grey. Don't believe it? Then scroll down.

The wikepedia page explains how to  prove the squares are the same, but the the link to a video did not work, so I decided to create one:

If the animation does not appear try this wmv file. (if it
fails to run just right click and save)

Other great optical illusions:

The St Louis Arch

The Hollow Mask (this links to a superb video of the illusion)

How many people in the picture?

Norman Fenton

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