The illusion due to psychologist Edward Bradford Titchener that a circle surrounded by other circles will appear smaller if the surrounding circles are enlarged. This effect is especially striking when comparing the cases where the surrounding circles are respectively smaller and larger than the middle circle, as in the illustration above in which the red circles are exactly the same size.
Titchener Illusion
See also
Delboeuf IllusionThis entry contributed by Margherita Barile
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References
National Science and Technology Centre, Australia. "Titchener Illusion Explanation." http://www.questacon.edu.au/html/titchener_illusion_explanation.html.Referenced on Wolfram|Alpha
Titchener IllusionCite this as:
Barile, Margherita. "Titchener Illusion." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/TitchenerIllusion.html