1. a phenomenon in stimulus generalization that occurs after discrimination training involving two stimuli along a common dimension (e.g., brightness). The peak of the response gradient (i.e., the point at which the organism shows maximum response) is shifted in a direction away from the less favorable stimulus (e.g., a dim light) to a point beyond the value of the stimulus associated with reinforcement (e.g., beyond the value of a bright light to that of a very bright light). 2. in aesthetics, the phenomenon in which a supernormal stimulus is preferred over the normal form of that stimulus.