Müller-Lyer illusion

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Science and technology

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What Wikipedia says

The Müller-Lyer illusion is an optical illusion consisting of three stylized arrows. When viewers are asked to place a mark on the figure at the midpoint, they tend to place it more towards the "tail" end. The illusion was devised by Franz Carl Müller-Lyer (1857–1916), a German sociologist, in 1889.

Excerpt from the Wikipedia article “Müller-Lyer illusion”, under the CC BY-SA 4.0 license. Read the article on Wikipedia

Image: Franz Carl Müller-Lyer, Franz Brentano, Public domain, via Wikimedia Commons.