A visual illusion in which a circle appears larger when surrounded by smaller circles than when surrounded by larger circles (see illustration). Also called the Titchener circles or Titchener illusion. [Named after the German psychologist Hermann von Ebbinghaus (1850–1909) who published a version of it in 1902, although the English psychologist Edward Bradford Titchener (1867–1927) had already discovered and published it in 1898]
Ebbinghaus illusion. The circles at the centre of each cluster are identical.