ABSTRACT
This chapter deals with the Adaptation-Level Theory and a factual confrontation with which it has been faced. The Adaptation-Level (AL) model has been used mainly in the analysis of size-contrast illusions, in which the apparent size of a test line gets smaller as it is put in larger and larger contexts. This sort of illusion seems to be an obvious application of a principle of perceptual relativity, the basic concept of AL theory.
