Encoding strategy and sleep interact to facilitate associative memory consolidation

Sleep benefits memory consolidation. However, factors present at initial encoding may moderate this effect. Here, we examined the role that encoding strategy plays in subsequent memory consolidation during sleep. Eighty-seven participants encoded pairs of words using two different strategies. Each participant encoded half of the word pairs using an integrative visualisation technique, where the two items were imagined in an integrated scene. The other half were encoded non-integratively, with each word pair item visualised separately. Memory was tested before and after a period of nocturnal sleep (N = 47) or daytime wake (N = 42) via cued recall tests. Immediate memory performance was significantly better for word pairs encoded using the integrative strategy compared to the non-integrative strategy (p < .001). When looking at the change in recall across the delay, there was significantly less forgetting of integrated word pairs across a night of sleep compared to a day spent awake (p < .001), with no significant difference in the non-integrated pairs (p = .19). These findings show that the strategy engaged in during encoding impacts both immediate retention of memories and the subsequent benefit of sleep versus wake on associative memory consolidation.