Checkerboard optical illusion

I like optical illusions because they remind us that seeing is not a passive experience of experiencing faithfully what is out there but involves a considerable amount of processing by the brain. Via Mark Frauenfelder here is another one that I found intriguing where just by placing pieces of paper in an arrangement, a regular checkerboard can be made to look as if it is bulging.


  1. DonDueed says

    That’s a really powerful illusion. I can trace individual lines and see that they’re really straight, but I can’t look at the overall board without seeing the “bulge”.

    There was a fascinating story on NPR today about people who lost, or never had, a “sense of location” — they can get lost on the way to the bathroom in their own house. It’s been traced to a problem in the hippocampus, which has three different kinds of cells that work together to maintain a picture of our position in space. (They must have to work overtime on the ISS!)

    I wonder if this illusion is also produced by some specialized cells in the optical processing system that get fooled by the regular-irregularities of the dot pattern. It might be enlightening to see the same pattern against a solid black background. I bet you’d still see a “bulge”; the checkerboard gets distorted because it’s interpreted as following that bulge.

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