Salience of central figure in the Ebbinghaus illusion: the Oreo cookie effect

The Ebbinghaus illusion was used to study size estimation as influenced by salient features of the central figure. Two groups of fourth graders, 9 boys and 11 girls, and two groups of seventh graders, 9 boys and 9 girls, judged the size of two central figures (an Oreo cookie or a black cardboard disc) with small and large black cardboard disc inducers. Responding showed the Oreo cookie was consistently perceived as larger than the cardboard disc when surrounded by the large inducing figures. The results are discussed in terms of an interaction between the geometric properties and salience of the central figure with the surrounds. This Oreo effect is not predicted by a strict version of the token-value hypothesis and differs from explanations based on contrast and conceptual similarity.