Infant-directed Speech Is Not Always Slower: Cross-linguistic Evidence from Dutch and Mandarin Chinese

It has been widely accepted that infant-directed speech (IDS) has a slower speaking rate than adult-directed speech (ADS) (e.g., Cristia, 2013), which is assumed to facilitate language development. This study aims at finding out whether this finding holds for Dutch and Mandarin Chinese and whether mothers slow down speaking rate to highlight unfamiliar words to children. Dutch and Mandarin Chinese mothers of 18-month-old children participated in a semi-spontaneous production task. They read a picture book to their child (IDS condition) and to an adult (ADS condition). The book contained target words that were unfamiliar or familiar to the child. We measured the speaking rate of the whole speech samples and the articulation rate of the utterances containing target words. Our results showed that language-specific properties exist: Dutch mothers generally slowed down in IDS in comparison with ADS, while Chinese mothers did not slow down in IDS. Also, Dutch mothers slowed down utterances containing unfamiliar words in IDS, but did not slow down utterances containing familiar words. This targeted speech rate pattern may function to facilitate word learning. However, unlike Dutch mothers, Chinese mothers did not slow down even when talking about unfamiliar words. Taken together, our results suggest that IDS is not always slower in IDS cross-linguistically, and provide evidence for the potential linguistic function of IDS.