The best known of all visual illusions, in which a line with inward-pointing arrowheads appears shorter than a line of the same length with reversed or outward-pointing arrowheads (see illustration). See also carpentered world, Morinaga misalignment illusion, star illusion, Zanforlin illusion. [Named after the German sociologist and psychiatrist Franz Carl Müller-Lyer (1857–1916) who discovered the illusion and published 15 versions of it in the journal Zeitschrift für Psychologie in 1889]
Müller-Lyer illusion. The horizontal lines are equal in length.