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Muller-Lyer Illusion
A visual image in which two identical lines appear to be of different lengths, because of depth cues provided by their surrounding features. In the Muller-Lyer illusion, two identical lines are presented, parallel to one another. One line is bordered at each end by an arrowhead, and the other line is bordered at each end by an inverted arrowhead. The line bordered by the arrowhead on each end appears to be shorter than the line bordered by the inverted arrowhead on each end, even though their lengths do not actually differ.
Although the complete explanation for this illusion is still under debate, a partial explanation involves the brain's interpretation of size and distance cues. When two objects, projecting the same-sized image onto the retina, appear to ...