Word form generalization across voices: The role of infant sleep

Infant sleep plays a crucial role in various aspects of language development, including the generalization of visual and auditory stimuli. The relative role of daytime naps and nocturnal sleep in these memory generalization processes is debated, with some studies observing significant generalization following a post-encoding nap and others observing it following nocturnal sleep, but only in cases where a post-encoding nap had occurred on the previous day. We conducted an online experiment with 8-month-old infants to determine whether a nap immediately following auditory exposure to words spoken by one talker enhances infants' recognition of the same word forms produced by a different talker (i.e., word form generalization). This ability involves the extraction of constant auditory features from a pool of variable auditory instances and thus is an example of memory generalization. Results revealed a significant increase in word form generalization after a night's sleep, specifically in infants who napped shortly after initial exposure to the words. This study provides the first evidence for the combined role of post-encoding naps and nocturnal sleep in phonological learning across different acoustic contexts. Phonological learning is frequently overlooked in research about word learning; however, prior to a child's ability to associate words and their meanings and to use language referentially they must first encode and access the phonological forms of words and recognize them in running speech. Therefore, the findings from this study contribute significantly to our understanding of vocabulary acquisition by highlighting the importance of daytime naps in phonological learning.