Napping facilitates word learning in early lexical development

Abstract

SUMMARYLittle is known about the role that night-time sleep and daytime naps play in early cognitive development. Our aim was to investigate how napping affects word learning in 16-month-olds. Thirty-four typically developing infants were assigned randomly to nap and wake groups. After teaching two novel object-word pairs to infants, we tested their initial performance with an intermodal preferential looking task in which infants are expected to increase their target looking time compared to a distracter after hearing its auditory label. A second test session followed after approximately a 2-h delay. The delay contained sleep for the nap group or no sleep for the wake group. Looking behaviour was measured with an automatic eyetracker. Vocabulary size was assessed using the Oxford Communicative Development Inventory. A significant interaction between group and session was found in preferential looking towards the target picture. The performance of the nap group increased after the nap, whereas that of the wake group did not change. The gain in performance correlated positively with the expressive vocabulary size in the nap group. These results indicate that daytime napping helps consolidate word learning in infancy. IN TROD UCTI ONInfants spend more than half the day sleeping and napping, yet they acquire new skills easily. One of the skills which develops rapidly during the second year of life is language. In particular, there is a dramatic increase in vocabulary size. In this study, we investigate how daytime napping enhances word learning in 16-month-old infants in order to shed light on the underlying mechanisms of language acquisition, and provide insight into the role and importance of napping and sleep.The enhancing role of sleep in memory consolidation and word learning is well-established in adults and older children. The memory-facilitating effects of sleep have been supported in a wide range of paradigms in adults (Diekelmann and Born, 2010;Rasch and Born, 2013), many of them using words as stimuli. Not only consolidation of recognition and recall of newly learnt words, but also their integration into existing neocortical networks and the mental lexicon are associated with sleep (Davis et al., 2009;Dumay and Gaskell, 2007;Tamminen et al., 2010). For children, some studies suggest that a period of offline consolidation is needed to stabilize new phonological representations . Brown et al. (2012) found that after familiarizing 7-and 12-year-old children with novel non-words (e.g. biscal) an improvement in a cued recall task was observed, but only after a 24-h period. Moreover, Henderson et al. (2012) have clarified that not only time but a period of sleep is needed to enhance performance on word recognition and cued recall tasks in 7-12-year-olds. Further enhancement has been found if 5-9-year-old children are taught the meanings of the newly learnt word forms (Henderson et al., 2013). Similarly, 6-12-year-olds show an improvement in recalling names of animal cartoons after sleep (Ashworth et al., 2014)....

Infant sleep and its relation with cognition and growth: a narrative review

“…In addition, a further experiment by the above researchers on a similar group of 15-month-old infants showed that the nap-dependent benefits towards language learning (where infants learnt abstract grammatical relations) persisted even after 24 hours 27. A recent study by a separate group of researchers also highlighted nap-dependent benefits towards language in terms of vocabulary learning 28. In the study, Horváth et al found that 16-month-old infants who napped after learning sets of new object–word associations spent more time looking at the correct associative pairing at the 2-hour delayed test session, whereas infants who remained awake did not display any differences in looking between the learning and delayed test sessions.…”

Sleep confers a benefit for retention of statistical language learning in 6.5 month old infants

“…Friedrich et al, 2015;Gómez et al, 2006;Horváth et al, 2015;Hupbach et al, 2009). Seehagen, Konrad, Herbert, andSchneider (2015), who tested memory in 6-month-olds, did not observe reduced retention across testing after a nap, but their test did not involve presenting inconsistent information from encoding.…”

“…Friedrich and Friederici (2011) reported an N400 event-related potential, indicative of semantic memory, for newly encoded word forms at 6 months that diminished significantly the next day. However, sleep soon after encoding aids new language retention in infants age 9 months and older (Friedrich, Wilhelm, Born, & Friederici, 2015;Gómez, Bootzin, & Nadel, 2006;Horváth, Myers, Foster, & Plunkett, 2015;Hupbach, Gómez, Bootzin, & Nadel, 2009). This led us to ask whether sleep will affect retention of new word learning at an earlier age.…”

Napping: A public health issue. From epidemiological to laboratory studies

“…In another study, Horvath et al studied word learning in 34 infants of 16 months using object-word associations 147 . After a 2-hour delay, memory performance increased for the nap group but not for the wake group.…”