The Effects of Age and Infant Hearing Status on Maternal Use of Prosodic Cues for Clause Boundaries in Speech

Abstract

Purpose The present study examined the effects of age and hearing status of a child on maternal use of pitch change, preboundary vowel lengthening, and pause duration, all of which are prosodic cues correlated with clause boundaries in infant-directed speech. Method Mothers' speech to infants with normal hearing (NH; n = 18), infants who are profoundly deaf with a cochlear implant (HI; n = 9), and an adult experimenter were recorded at 2 time periods separated by 6 months. NH infants were matched to HI infants by chronological age or hearing experience. Fundamental frequency of pre- and postboundary vowels, vowel duration, and pause duration between utterances was measured. Results Results demonstrated that mothers (a) exaggerated prosodic characteristics in infant-directed speech regardless of infants' hearing status; (b) tailored preboundary vowel lengthening to infants' hearing experience rather than to chronological age; and (c) decreased exaggeration of pause duration over time. Conclusions The results suggest that acoustic cues correlated with clause boundaries are available in maternal speech to HI infants. Their exaggeration relative to adult-directed speech suggests that mothers' use of infant-directed speech is a natural behavior regardless of infant hearing status. Finally, mothers modify speech prosody according to their children’s age and hearing experience.