Effects of spacing on memory for homogeneous lists.

The spacing effect refers to the advantage in memory for information repeated at separate points of time over information repeated in massed fashion. Three experiments showed that no spacing effect was found in free recall of lists containing items of high interstimulus semantic similarity. However, spacing effects were found when recognition or frequency-discrimination tests were given on these materials. The results support the hypothesis that several distinct processes underlie the spacing effect. Repeated information i s generally remembered better when i t i s presented a t widely spaced times than when presented in massed fashion. This spacing effect is one of the most widespread of memory phenomena, occurring on many different kinds of tests (e.g., free recall, recognition, word completion, perceptual identification), with many dif- ferent kinds of materials (e.g., words, pictures, prose), and using many different subject populations (e.g., preschool children, young adults, older people). Numerous theories have been developed to explain the spacing effect (for re- views, see Crowder, 1976; Greene, 1989; Hintzman, 1974,