Sleep-Associated Consolidation of New Word Acquisition in Adults and Children.

Research indicates that a prolonged period of time is needed for a new word to become integrated with the existing lexicon and generate stable and long-lasting memory representations, with sleep playing an important role in the offline consolidation of this process. Understanding how this process might change over development is crucial, given the considerable variability in both sleep and language learning processes across development. Moreover, previous research often utilizes unnatural learning contexts and focus on acquisition of fictitious words or words from unfamiliar languages (especially with adult participants). This study aims to investigate whether sleep- effects occur in learning of real words and explore how these sleep-associated mechanisms in new word acquisition may vary between adults and children.
Two experiments were conducted to examine acquisition of rare Chinese words with
44 Chinese-speaking adults (Experiment 1) and 70 boarding school children (have very
consistent sleep patterns) aged between 8-12 years (Experiment 2). Participants were
randomly assigned to a sleep-wake or a wake-sleep group, in which they learned 9 names of ancient Chinese animals (the names were made up of characters known to both adults and children, see Figure 1) at 8pm or 8am respectively (see figure 2). Their memory was assessed immediately, 12 and 24 hours later via rapid naming (explicit recall), word definition (explicit declarative knowledge) and size judgement tasks (an implicit test of semantic access/integration) to probe different aspects of word knowledge. Results in adults showed that sleep, as compared to wake periods, was associated with significant improvements in both explicit recall and semantic integration. Moreover, 24 hours post-learning, adults in the sleep-wake group demonstrated greater improvements as compared to the wake-sleep group, suggesting an active role of sleep-associated word consolidation that persisted over
subsequent waking periods. On the other hand, children exhibited significant overnight gains in semantic integration when tested 12 and 24 hrs after learning. Although their performance in explicit declarative knowledge showed equivalent improvement across sleep and wake periods when tested after 12 hours, sleep-associated benefit was observed at the 24-hour retest.
Our results showed similar sleep-associated benefits in the integration of word
semantics in both children and adults, while the time course of the effects on explicit
knowledge retention may vary across the two groups. The developmental trajectory of sleep-dependent consolidation processes in word acquisition will be discussed.