The roles of working memory and intervening task difficulty in determining the benefits of repetition.

Memory is better when learning events are spaced, as compared with massed (i.e., the spacing effect). Recent theories posit that retrieval of an item's earlier presentation contributes to the spacing effect, which suggests that individual differences in the ability to retrieve an earlier event may influence the benefit of spaced repetition. The present study examined (1) the difficulty of task demands between repetitions, which should modulate the ability to retrieve the earlier information, and (2) individual differences in working memory in a spaced repetition paradigm. Across two experiments, participants studied a word set twice, each separated by an interval where duration was held constant, and the difficulty of the intervening task was manipulated. After a short retention interval following the second presentation, participants recalled the word set. Those who scored high on working memory measures benefited more from repeated study than did those who scored lower on working memory measures, regardless of task difficulty. Critically, a crossover interaction was observed between working memory and intervening task difficulty: Individuals with low working memory scores benefited more when task difficulty was easy than when it was difficult, but individuals with high working memory scores produced the opposite effect. These results suggest that individual differences in working memory should be considered in optimizing the benefits of repetition learning.