Lip movement exaggerations during infant-directed speech.
OBJECTIVE
Although a growing body of literature has identified the positive effects of visual speech on speech and language learning, oral movements of infant-directed speech (IDS) have rarely been studied. This investigation used 3-dimensional motion capture technology to describe how mothers modify their lip movements when talking to their infants.


METHODS
Lip movements were recorded from 25 mothers as they spoke to their infants and other adults. Lip shapes were analyzed for differences across speaking conditions. The maximum fundamental frequency, duration, acoustic intensity, and first and second formant frequency of each vowel also were measured.


RESULTS
Lip movements were significantly larger during IDS than during adult-directed speech, although the exaggerations were vowel specific. All of the vowels produced during IDS were characterized by an elevated vocal pitch and a slowed speaking rate when compared with vowels produced during adult-directed speech.


CONCLUSIONS
The pattern of lip-shape exaggerations did not provide support for the hypothesis that mothers produce exemplar visual models of vowels during IDS. Future work is required to determine whether the observed increases in vertical lip aperture engender visual and acoustic enhancements that facilitate the early learning of speech.
Green
Jordan R
JR
Department of Special Education and Communication Disorders, University of Nebraska-Lincoln, 318 Barkley Center, Lincoln, NE 68583, USA. jgreen4@unl.edu
Nip
Ignatius S B
IS
Wilson
Erin M
EM
Mefferd
Antje S
AS
Yunusova
Yana
Y
D000328:Adult; D001696:Biomechanical Phenomena; D005145:Face / Q000502:physiology; D005260:Female; D006801:Humans; D007223:Infant; D007804:Language Development; D008046:Lip / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009035:Mothers; D009068:Movement / Q000502:physiology*; D010700:Phonetics; D011932:Reading; D013060:Speech / Q000502:physiology*; D014743:Videotape Recording; D055815:Young Adult