Prosody and Function Words Cue the Acquisition of Word Meanings in 18-Month-Old Infants

Language acquisition presents a formidable task for infants, for whom word learning is a crucial yet challenging step. Syntax (the rules for combining words into sentences) has been robustly shown to be a cue to word meaning. But how can infants access syntactic information when they are still acquiring the meanings of words? We investigated the contribution of two cues that may help infants break into the syntax and give a boost to their lexical acquisition: phrasal prosody (speech melody) and function words, both of which are accessible early in life and correlate with syntactic structure in the world’s languages. We show that 18-month-old infants use prosody and function words to recover sentences’ syntactic structure, which in turn constrains the possible meanings of novel words: Participants (N = 48 in each of two experiments) interpreted a novel word as referring to either an object or an action, given its position within the prosodic-syntactic structure of sentences.