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Motion helps you see things you might miss otherwise.
  • Click and hold to stop a shape's movement across the colored background.

  • What do you see when you stop the shape inside the colored background? What if it's only partially inside?
If a bird comes upon a grasshopper in a bush, the grasshopper may freeze in its tracks. Why? Because the grasshopper has evolved to protect itself by blending in with its surroundings, like the camouflaged object in this simulation. And one way to blend in is to stop moving—because motion reveals the edges that separate a creature from the background.
Of course, predators can play that game too. For example, watch a cat sneak up on a bird. If the bird begins to take notice, the cat freezes in place. In the dangerous world of predator and prey, motion is a dead giveaway—which is why motion detection is such an important characteristic of most animals’ visual systems.

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