Illusion explained

10 Sep

A good example of the Cafe Wall Illusion.

Why Evolution Is True

Well, sort of, because it’s long and complicated, and you might not want to go through it. This drawing, which I presented yesterday, is a version of the Café Wall Illusion (the link tells you how it got its name). The lines look curved, but are really straight, as you can check with a ruler or piece of paper:


It also comes in a version lines that don’t appear wavy, but tilted:


The explanation is given in an online paper (reprinted from Perception [1979]) by Richard Gregory and Priscilla Heard.  It involves the luminescence of the squares, the width and luminescence of the separating “mortar” lines, and the degree of offset of the squares.

If you click on the screenshot below, you can go to a site where you can vary these things with slider buttons, and see how they affect the illusion:

Screen Shot 2014-09-09 at 6.19.48 AM

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