Distinctiveness and repetition in item recognition

We scrutinized the hypothesis that the distinctiveness of unrepeated stimuli yields an enhancement of their memorability, when contrasted with repeated stimuli. In three conditions of a variant of von Restorff's (1933) isolation paradigm, unrepeated stimuli were respectively rendered either distinctive, by intermixing them with repeated stimuli from a different category, or nondistinctive, by having both unrepeated and repeated items originate in the same category or categories. The recognition-memory strength difference between unrepeated and repeated stimuli, in terms of a signal-detection measure of sensitivity, was less when the unrepeated stimuli were distinctive than when they were not distinctive. This implies that the relative weakness of unrepeated stimuli may be offset by distinctiveness that accrues from their infrequency. These findings are considered with reference to contemporary theoretical treatments of distinctiveness.