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Müller-Lyer
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Moon
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Illusion Pairs

Turn over two cards at a time. Match each picture to its name.

Useless’s lab notes: measured twice, rubbed out once

Jastrow said: “We judge relatively, even when we most desire to judge absolutely.” I judge relatively too. Next to a pencil sharpener, I’m enormous.

— U. (tap me for another)

Thanks for visiting. Trust your ruler, not your eyes.

The illusions

Müller-Lyer arrows
Ebbinghaus & Delboeuf circles
Ponzo & size constancy
The moon illusion
The Ames room
The T, Jastrow & sine
Experiments to try
Who found them

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The big facts page
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Useless’s lab notes

Helping

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The network

More illusions at illusions.im
About the network

size.illusions.im is part of the ReallyByte network, run by REALLYBYTE, based in the Isle of Man. Facts are checked against Michael Bach’s Optical Illusions & Visual Phenomena, Encyclopaedia Britannica and the Exploratorium, listed on the sources page (checked 31 Oct 2026). The illusion drawings and games are our own; photos are public domain or CC0, credited. Not affiliated with or endorsed by Michael Bach, Britannica or the Exploratorium. As an Amazon Associate I earn from qualifying purchases. No cookies; privacy-friendly visit counts via GoatCounter. Privacy | Contact

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