Over the centuries, artists have learned to force perspective, and to make it seem that paintings are lit from within. But the images you’ll find in Scientific American’s online history of optical illusions go one step further: They make us see movement where no movement exists.
The oldest example was created by neuroscientist Donald MacKay, in 1957; it illustrates the still-unexplained effect that dense radial lines have on the human eye. Later illusions — by the op artist Bridget Riley and the neuroscientist Ayiyoshi Kitaoka — depend on tiny, side-to-side eye movements (called micro-saccades) to create the impression of spin or acceleration. And the rotating-tilted-lines illusion works only if you move your entire head closer or farther away. Taken together, these images prove a point that visual neuroscientists come up against every day: In some respects, everything we perceive is a function of our imagination.
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