The Delboeuf illusion was described by Joseph Delboeuf (1865), a Belgian philosopher and experimental psychologist. If the same circle is placed inside two different concentric circles, its size will apparently vary.
Delboeuf Illusion
See also
Titchener IllusionThis entry contributed by Margherita Barile
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References
Delboeuf, J. "Seconde note sur de nouvelles illusions d'optique: Essai d'une théorie psychophysique de la manière dont l'oeil apprécie les grandeurs." Bulletins de l'Académie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique, 2e série, 20, 70-97, 1865.Nagoya Visual Illusion Experts Group. "Delboeuf Illusion." http://humanities.lit.nagoya-u.ac.jp/~illusion/gallery/NVEG/standard/Delboeuf01_e.html.Referenced on Wolfram|Alpha
Delboeuf IllusionCite this as:
Weisstein, Eric W., with contributions by Margherita Barile. "Delboeuf Illusion." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/DelboeufIllusion.html