Infant-directed speech reduces English-learning infants preference for strong/weak versus weak/strong words

Abstract

Mounting evidence suggests that infant-directed speech (IDS) facilitates aspects of language acquisition. An important milestone of English-learning infants' language acquisition is encoding the predominant stress-initial rhythmic structure of English, which 9-month-olds have demonstrated by showing a looking-time preference for lists of strong/weak words (e.g., doctor) versus weak/strong words (e.g., guitar) (Jusczyk et al., 1993). We tested for this preference in 48 9-month-olds using the headturn preference procedure. Twenty-four infants were presented with the words using IDS, and 24 were presented with adult-directed speech (ADS). Infants were presented with a visual display of a blinking light on one of two (left and right) monitors. When they oriented toward the monitor, a list was presented from behind that monitor until they looked away for more than 2 s. They were presented with lists of weak/strong words for half the trials and strong/weak words for the other half in quasi-random order. A repeated-measures AVOVA revealed a statistically significant interaction between word-type preference and speech condition. To our surprise, only infants in the ADS condition showed a preference strong/weak words. The findings raise the possibility that rhythmic properties of words may be more difficult for infants to encode in IDS than ADS.