Abstract: Directed forgetting is a new experimental paradigm for use in the study of memory. Retrieval inhibition theory offers a widely accepted account of the list-method directed forgetting effect, but little is known about the exact mechanism that produces it. One possibility is that inhibition results from retrieval practice. Indeed, many studies show that retrieval inhibition underlies the directed forgetting effect can be interpreted as consistent with the retrieval-induced forgetting interpretation. Drawing on the retrieval-induced forgetting, we hypothesized that (a) the directed forgetting effect would be greater with additional retrieval practice tests on a target word list than without and (b) the directed forgetting effect would increase with increasing amounts of interpolated retrieval practice.
One hundred and twenty undergraduate students participated in Experiment 1 and eighty in Experiment 2. In both experiments, participants studied items from two word lists - List 1 and List 2. Participants in the directed forgetting and remember groups were given different instructions. The directed forgetting groups were told that list 1 was just for practice and should be forgotten and that list 2 was the one to be remembered; in contrast, participants in the remembering groups were told to remember both list 1 and list 2. After studying both lists, participants were given one, three or no retrieval practice tests on list 2. In Experiment 1, before each retrieval practice test, participants were instructed to recall as many characters as they could from list 2; Experiment 2 was the same as Experiment 1 except that participants completed a stem completion test to facilitate their overall recall of list 2 items (as opposed to a pure recall test). Finally, participants were required to recall as many items as they could from list 1 and list 2. A three-factor mixed analysis of variance (ANOVA) was performed with group (directed forgetting and remembering) and number of retrieval practice tests (0, 1, and 3) as between-subjects factors and list (List 1 and List 2) as a within-subjects factor.
The results showed that in Experiment 1, the magnitude of the directed forgetting effect disappeared with increasing amounts of retrieval practice; in Experiment 2 which used the stem-completion test to increase retrieval success, the magnitude of the directed forgetting effect was increased and the participants in the forgetting instruction group inhibited list 1 items.
The results confirmed that retrieval success can increase the directed forgetting effect, indicating that retrieval success can account for retrieval inhibition in directed forgetting

Key words: directed forgetting, retrieval-induced forgetting, retrieval practice, retrieval success