Franz Carl Müller-Lyer

Franz Carl Müller-Lyer, born Francis Xavier Hermann Müller (5 February 1857 - 29 October 1916) was a German psychologist and sociologist. The Müller-Lyer illusion is named after him.

Müller-Lyer was born in Baden-Baden. He studied medicine at the Universities of Strasbourg, Bonn, and Leipzig. He also studied psychology and sociology at the Universities of Berlin, Vienna, Paris and London.

In 1888 he entered into private practice in Munich.

The optical illusion he described in 1889 involves the perception of the length of a line when the ends are capped by chevrons. Diverging chevrons seem to make the line longer when compared with converging chevrons. There are numerous similar geometrical illusions known now.

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