This study measured longitudinal change in six parameters of infant utterances (i.e. number of sounds, CV syllables, supraglottal consonants, and repetitions per utterance, temporal duration, and seconds per sound), investigated previously unexplored characteristics of repetition (i.e. number of vowel and CV syllable repetitions per utterance) and analyzed change in vocalizations in relation to age and developmental milestones using multilevel models. Infants (N=18) were videotaped bimonthly during naturalistic and semi-structured activities between 0 ; 3 and the onset of word use (M=11·8 months). Results showed that infant utterances changed in predictable ways both in relation to age and in relation to language milestones (i.e. reduplicated babble onset, word comprehension and word production). Looking at change in relation to the milestones of language development led to new views of babbling, the transition from babbling to first words, and processes that may underlie these transitions.
(Received January 21 2007)
(Revised August 24 2007)
(Online publication October 16 2008)
[*] This paper is based on a project submitted to the University of Missouri-Columbia in partial fulfillment of the requirements for the doctoral degree. Portions of this research were presented at the annual meeting of the American Speech-Language-Hearing Association, Philadelphia, PA, November 2004. This research was supported in part by a graduate research grant from the University of Missouri, Department of Psychological Sciences, to the author and a grant from the National Institutes of Health (R01 HD41607) to Jana M. Iverson. I thank Jana Iverson, Judith Goodman, Nelson Cowan, Jonathan King and Dave Geary for their contributions to this project, and Jennifer Krull for invaluable assistance with multilevel models. I thank Ray Bacon for assistance in creating plots of the data, Jeanine Jesberg and Mona Chawla for assistance with reliability, Eugene Buder for initial ideas for the design of vests, Jean Jesberg for constructing the vests, and members of the University of Missouri, Infant Communication Laboratory for extensive assistance with data collection. Special thanks to the families who shared their infants' development for seventeen months. Mary K. Fagan is now at Indiana University.