The brain deals with this problem using a toolkit of assumptions. And the brain does a good job—it can easily beat computerized shape-spotters when scanning pictures, faces, and moving scenes. However, the brain’s eagerness to find shapes also leads it to find shapes where there aren’t any, as with the white triangle at the forefront of the following picture.
When confronted with this picture, your brain doesn’t need to conjure up a white triangle. There’s a reasonable alternate explanation—that the image contains three pacman-like circles with wedges cut out of them, and the wedges are lined up with the gaps between the blue triangles inside. However, a just-so arrangement like this would be unlikely in the natural world, so your brain quickly dismisses that possibility. In essence, your brain picks up on a few clues and performs a rapid analysis to determine the most likely explanation. However, you don’t merely think about that most likely explanation, you also see it. If you rotate the pacmen around, the illusion disappears, and the image reverts to a collection of harmless shapes.
Perception
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