Effects of sleep and retrieval practice on verbal paired-associate learning across 12 and 24 hours

The rapid consolidation hypothesis (Antony et al., Trends in Cognitive Science, 21, 573-576, 2017) proposes that sleep and retrieval practice may both represent a memory consolidation event, and thus, have overlapping effects on memory retention. We tested this hypothesis in two experiments using verbal paired-associate learning. In both experiments, participants studied 60 word pairs, which were either restudied or retrieved (without feedback) in a subsequent practice phase. After a retention interval, participants completed a cued recall task on all word pairs. In Experiment 1, the retention interval lasted 12 hours, during which half of the participants had a period of overnight sleep (Sleep group) whereas the other half engaged in daytime activities (Wake group). Here, in line with prior studies, we found that while sleep (vs. wake) benefitted the restudied pairs, it had no significant effect on the retrieved pairs. This suggests that retrieval practice may serve to consolidate memories, rendering subsequent sleep-related consolidation of little relevance. Then, to test whether the sleep benefit in the restudy condition was due to active sleep consolidation or passive protection, Experiment 2 extended the retention interval to 24 hours, during which half of the participants slept shortly after the practice phase while the other half slept 12-15 hours later. Here, we observed the classic testing effect (i.e., Retrieval > Restudy), and we also found that the two groups performed similarly in both the restudy and retrieval conditions, consistent with a passive role for sleep. Overall, our findings provide some support for the rapid consolidation hypothesis but suggest that the effect of sleep on memory retention for word pairs is more transient than that of retrieval practice.