Ebbinghaus Illusion

The Ebbinghaus illusion, also known as Titchener circles, is an optical illusion on size perception as influenced by the sizes of surrounding objects or shapes. The most usual example is a comparison of two identical circles.

For instance, circle A is surrounded by much bigger circles while circle B is surrounded by much smaller circles. Even if circles A and B have the same size, circle A appears smaller due to its marked contrast with the bigger circles around it. This was introduced by Hermann Ebbinghaus, a German psychologist, and popularized by Edward Titchener, an English psychologist, in the English-speaking countries.