Popular Science Feature - Chessboard Optical Illusion

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Feature - The Checkerboard Optical Illusion

Shadows are the topic of a book recently reviewed on the Popular Science website (The Shadow Club by Roberto Casati) - it's nothing to do with the book, but here's a stunning optical illusion featuring shadow:

This optical illusion is reproduced with the permission of Professor Edward Adelson of M.I.T. Click here for details on the Professor's site. Thanks also to Andy Grüneberg for bringing this to our attention.

This is simply the best optical illusion we've ever seen. It illustrates why the really interesting thing about shadows is not what they are - simply the absence of light, contrasted against an area where light is hitting - but how our brains perceive them:

If you have any doubts, import the picture into a graphics program like Paint and cut out and copy the squares to put them alongside each other. The result will be like this:

Reader's Comment: Gary Doran

You can also print the picture, cut out block A and B and place them side by side. Even the printer prints them the same shade of grey. It's like the printer does not see the shadow, only our brain does.

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