Sleep reduces the testing effect—But not after corrective feedback and prolonged retention interval.

Retrieval practice relative to restudy of learned material typically attenuates time-dependent forgetting. A recent study examining this testing effect across 12-h delays filled with nocturnal sleep versus daytime wakefulness, however, showed that sleep directly following encoding benefited recall of restudied but not of retrieval practiced items, which reduced, and even eliminated, the testing effect after sleep (Bauml, Holterman, & Abel, 2014). The present study investigated, in 4 experiments, whether this modulating role of sleep for the testing effect is influenced by two factors that have previously been shown to increase the testing effect: corrective feedback and prolonged retention intervals. Experiments 1a and 1b applied 12-h delays and showed benefits of sleep for recall after both restudy and retrieval practice with feedback, but not after retrieval practice without feedback. Experiments 2a and 2b applied 24-h or 7-day delays and failed to observe any long-lasting benefits of sleep directly after encoding, on both restudied and retrieval practiced items. These results indicate that both corrective feedback and prolonged retention intervals reduce the modulating role of sleep for the testing effect as it can be observed after 12-h delays and in the absence of corrective feedback, which suggests a fairly limited influence of sleep on the effect