Solved: How Optical Illusion Turns Circles Into Hexagons

msnbc:

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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Dr Hiroyuki Ito’s results are interesting but no proof for “form changes in after images”. The change in form appears to show up immediately during fixation of the test figure (viz not only during the after image). Furthermore, if one fixates one of the circles (in stead of the little cross in the center)thát fixated circle does not change in form (both during fixation and during the after image); the other circles (more periphere in the visual field) however do change. This might be an indication that the phenomenon of form change belongs to the category of lateral inhibition in the retina, such as for instance the Hering grid.
One final remark: feature detecors for form characteristics have a central (cortical) representetion, whereas color detectors are retinal. This is apparent from the fact that colour after effects do not show eye transfer (fixating with one eye and looking to the after image with the other)whereas movement after-effects show eye transfer.

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