Influences of Retrieval Processes on the Spacing Effect in Free Recall

A two-process theory of the spacing effect in free recall is presented and tested. The first process, differential organization, produces a positive correlation between the spacing of the presentations of repeated words and the number of different retrieval routes that can provide access to the words. The retrieval process interacts with the differential organization to control performance. If the cues used to retrieve the words provide approximately equal access to all retrieval routes, then the function relating spacing to recall will increase monotonically. If only selected retrieval routes are used, then the spacing function will be nonmonotonic. Evidence supporting this theory is that (a) the monotonic spacing function is most robust when subjects study the list using an organizational strategy, (b) cuing and directing retrieval with input words can result in a nonmonotonic effect of spacing when subjects have used an organizational strategy, and (c) directing retrieval by instructions about the order of recall can result in a nonmonotonic effect of spacing.