Infant-directed speech reduces English-learning infants' preference for trochaic words.

Over the past couple of decades, research has established that (1) infant-directed speech (IDS) facilitates speech, language, and cognitive development; and (2) infants are sensitive to the rhythmic structures in the ambient language. However, little is known about the role of IDS in infants' processing of rhythmic structures. Building on these two lines of research, whether IDS enhances infants' sensitivity to the predominant stress pattern (trochaic) in English was asked. To address this question, 9-month-old American infants were familiarized and tested with both trochaic (e.g., lazy) and iambic (e.g., cartoon) words presented in either IDS or adult-directed speech (ADS). Infants showed listening preference for the trochaic over iambic words when the speech was presented in ADS, but not in IDS. These results suggest that IDS attenuates infants' preference for trochaic stress pattern. Further acoustical analyses demonstrated that IDS provided less salient spectral cues for the contrasts between stressed and unstressed syllables in trochaic words. These findings encourage further efforts to explore the effects of IDS on language acquisition from a broader perspective.