Two separate lines of research have examined the influence of song and infant-directed speech (IDS-a speech register that includes some melodic features) on language learning, suggesting that the use of musical attributes in speech input can enhance language learning. However, the benefits of these two types of stimuli have never been directly compared. In this investigation, we compared the effects of song and IDS for immediate word learning and long-term memory of the learned words. This study examines whether the highly musical stimuli (i.e., song) would facilitate language learning more than the less musical stimuli (i.e., IDS). English-speaking adults were administered a word learning task, with Mandarin Chinese words presented in adult-directed speech (ADS), IDS, or song. Participants' word learning performance was assessed immediately after the word learning task (immediate word learning) and then 1 day later (long-term memory). Results showed that both song and IDS facilitated immediate word learning and long-term memory of the words; however, this facilitative effect did not differ between IDS and song, suggesting that the relationship between the degree of musicality and language learning performance is not linear. In addition, song and IDS were found to facilitate the word association process (mapping a label to its referent) rather than the word recognition process. Finally, participants' confidence in their answers might not differ among ADS, IDS, and sung words.
Keywords: Music; infant-directed speech; language learning; memory; song.