Meaning of Müller-Lyer illusion

Mül'ler-Ly'er illu"sion

Pronunciation: (mul'ur-lī'ur, my'lur-, mil'ur- Ger. myl'ur-lē'ur), [key]
  1. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.