Ehrenstein Contour Illusion

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The area between radial lines appears brighter than the background. This apparent discrepancy in brightness produces the illusion of circles or squares in between the radial lines. This contour illusion was found by the German psychologist Walter Ehrenstein in 1941.
Contributed by: Michael Schreiber (March 2011)
Open content licensed under CC BY-NC-SA
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"Ehrenstein Contour Illusion"
http://demonstrations.wolfram.com/EhrensteinContourIllusion/
Wolfram Demonstrations Project
Published: March 7 2011