Müller-Lyer illusion

[ muhl-er-lahy-er, myoo-ler-, mil-er-; German myl-uhr-lee-uhr ]
/ ˈmʌl ərˈlaɪ ər, ˈmyu lər-, ˈmɪl ər-; German ˈmül ərˈli ər /


a geometric illusion in which two lines of equal length appear unequal depending on whether angular lines forming arrowheads at each end point toward or away from each other.

Origin of Müller-Lyer illusion

after Franz-Karl Müller-Lyer (1857–1916), German sociologist, who described the illusion in 1889
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British Dictionary definitions for muller-lyer illusion

Müller-Lyer illusion
/ (ˈmuːləˈlaɪə) /


an optical illusion in which a line with inward pointing arrowheads is seen as longer than an equal line with outward pointing arrowheads

Word Origin for Müller-Lyer illusion

C19: named after Franz Müller-Lyer (1857–1916), German sociologist and psychiatrist
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012