The subtlety of distinctiveness: What von Restorff really did.

The isolation effect is a well-known memory phenomenon whose discovery is frequently attributed to von Restorff (1933). If all but one item of a list are similar on some dimension, memory for the different item will be enhanced. Modern theory of the isolation effect emphasizes perceptual salience and accompanying differential attention to the isolated item as necessary for enhanced memory. In fact, von Restorff, whose paper is not available in English, presented evidence that perceptual salience is not necessary for the isolation effect. She further argued that the difference between the isolated and surrounding items is not sufficient to produce isolation effects but must be considered in the context of similarity. Von Restorff's reasoning and data have implications for the use of distinctiveness in contemporary memory research, where distinctiveness is sometimes defined as perceptual salience and sometimes as a theoretical process of discrimination. As a theoretical construct, distinctiveness is a useful description of the effects of differences even in the absence of perceptual salience, but distinctiveness must be used in conjunction with constructs referring to similarity to provide an adequate account of the isolation effect and probably any other memory phenomena.