A Daytime Nap Facilitates Generalization of Word Meanings in Young Toddlers.

STUDY OBJECTIVES: One of the key processes in language development is generalization--the selection and extension of relevant features and information to similar objects and concepts. Little is known about how sleep influences generalization, and studies on the topic are inconclusive. Our aim was to investigate how a nap affects generalization in 16-mo-olds. We hypothesized that a nap is necessary for successful generalization of word meanings. METHODS: Twenty-eight 16-mo-old, typically developing toddlers were randomly assigned to nap and wake groups. We trained toddlers with two novel object-word pairs and tested their initial ability to generalize. Toddlers took part in an intermodal preferential looking task, in which they were shown different colored versions of the original objects and heard one of the trained labels. If toddlers understand the label, they are expected to increase their looking time to the target. Looking behavior was measured with an automated eye tracker. Afterward, the nap group went to sleep, while the wake group stayed awake for approximately 2 h. We then repeated the test of their performance on the generalization task. RESULTS: A significant interaction of group and session was found in preferential looking. The performance of the nap group increased after the nap, whereas that of the wake group did not change. CONCLUSIONS: Our results suggest that napping improves generalization in toddlers.