When you stare at a colorful image and then turn to look at a neutral background, a “ghost image” appears in contrasting colors. Now, new research finds that a similar illusion occurs with shapes, turning circles into hexagons and vice versa.
Though similar, the two visual phenomena have different causes. While the color optical illusion, occurs because of tired-out light-sensing cells in the eye, the shape afterimage illusion arises from the visual parts of the brain, said study researcher Hiroyuki Ito, of Kyushu University in Japan.
“Afterimages are generally unnoticed or blurred,” Ito wrote in an email to LiveScience. But for scientists, the images can offer tantalizing clues as to what’s going on in the brain.
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