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Do We Perceive Reality? The Checker Shadow Illusion

From Jerry Coyne's Blog:

I recently finished Steve Pinker’s The Blank Slate (recommended!), and in one chapter was taken by his discussion about whether human senses perceive a real, external reality or whether that reality is somehow “constructed” socially or by our senses. If you’ve read the book, you know that Pinker comes down on the “it’s real” side (this solution is obvious to all but a moron*)—but not always: what we perceive as “real” is sometimes distorted by our expectations. That, of course, is the basis of optical illusions.

One of Pinker’s examples was the famous “checker shadow illusion,” which completely bamboozled me. In case you haven’t seen it, I’ll reproduce it here.

Take a look at this checkerboard, and at squares A and B. They’re different shades, right?

Nope—they are exactly the same color and shade!

Don’t believe it? (I didn’t.) Check out this video, which connects those two squares with a like-colored bar, demonstrating that they’re the same:




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