Poggendorff illusion
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The Poggendorff Illusion is an optical illusion that involves the brain's perception of the interaction between diagonal lines and horizontal and vertical edges. It is named after Johann Poggendorff (1796-1877), a German physicist who first described it in 1860.
In the picture to the right, a straight black line is obscured by a red rectangle. The black line appears disjointed, although it is in fact straight; the second picture illustrates this fact.
