Fig. 1.

Retrieval practice induces forgetting of competing memories. a The three phases of Experiment 1 (encoding, practice, test) for the three conditions. During encoding, rats associated arena contexts (different arenas depicted as distinct colored shapes) to two copies of each of two objects (distinct letters indicate different objects; numbers indicate copies). After encoding, rats retrieved one of the objects three times during practice via a novelty preference procedure in which they were exposed to an encoded object with a contextually novel object. The final test paired the competitor (e.g., B) or the practiced item (e.g., A) with a fully novel object. The interference and time control conditions replaced practice with novel object encoding sessions and time in the home cage, respectively. b (Left). The assumed retrieval dynamics during practice. Efforts to retrieve object A during exploration elicit competition from the memory for B, triggering control processes to inhibit B. Inhibition’s persisting aftereffects hinder retrieval of B during test. (Right) During practice, the number of seconds that animals explored the practiced and contextually novel objects during the three trials. Individual values used to calculate the mean and SEM are presented as dots. Practiced object exploration diminished across trials, indicating increased familiarity. Values are means ± SEM. *p = 0.033, **p = 0.003, one-tailed paired t test; effect sizes (d): d = 0.83 (X vs. A); d = 0.90 (Y vs. A); d = 4.34 (Z vs. A). c (Left) Discrimination index means ± SEM calculated from the exploration times during test. *p = 0.024 (t₃₃ = 3.08), d = 1.12 (RP vs. IC); *p = 0.0130 (t₃₃ = 3.32), d = 1.21 (RP vs. TC); p = 0.0013 (t₃₃ = 4.15), d = 1.52 (RP vs. RP+), Bonferroni post hoc comparisons after a repeated-measures ANOVA, n = 12 animals. Discrimination index = (novel-object exploration time − familiar object exploration time)/total exploration time. Recognition of the competitor object B was impaired relative to interference and time controls. (Right) Absolute exploration times in seconds during test. The novel and the competitor objects were explored equally after retrieval practice, but not in the other conditions. Values are means ± SEM. *p < 0.05 and **p < 0.01, NS = not significant. Paired t test, n = 12 animals