The Role of Sleep in Retention and Generalization of Statistically Learned Language

Abstract

Across the lifespan, learners capitalize on regularities in language to find words in fluent speech and learn grammatical patterns, a process called statistical learning. Much of this research has focused on encoding, and few studies have investigated whether this type of knowledge is long-lasting. Related to retention, sleep promotes stabilization of memories in adulthood, with a growing literature on the benefits of sleep for memory in infants and children. In 5 studies, we examined the role of sleep in retention and generalization of statistically learned language. Specifically, 13-month-olds learned the order of syllables within words, discriminating words with the correct order from words with a reversed syllable order (Exp. 1), but they do not retain this level of detail across a nap (Exp. 2). Looking at the same type of learning in adults (Exp. 3), the group who slept after learning failed to show retention. Further analyses revealed an association between total sleep and memory for syllable order, indicating more sleep after learning related to retention. On the other hand, a group of wakefulness participants remembered which syllables formed words but not their correct order, and correlations showed they retained order after wakefulness if they encoded it during learning. Lastly, we demonstrated that sleep stabilized memory for grammatical patterns in 18-month-olds, promoting specific memory for learned phrases (Exp. 4). Additionally, only infants who napped after learning generalized their knowledge of the pattern to completely novel phrases (Exp. 5). Overall, our data suggest sleep does not benefit detailed representations earlier in infancy, but it promotes specific and abstract memory by 18 months. Furthermore, sleep relates to retention of order in adults, though wakefulness participants also showed retention. Future studies can elucidate how the effect of sleep develops, and whether sleeping after statistical learning in adulthood promotes memory for order more so than wakefulness.