Date of Completion


Embargo Period



motor-vocal coordination, motor development, babbling, rhythmic behaviors

Major Advisor

Dr. James Green

Associate Advisor

Dr. Heather Bortfeld

Associate Advisor

Dr. Heather Read

Field of Study



Doctor of Philosophy

Open Access

Open Access


In adults, speech and gesture are very much intertwined with each other, but it remains unclear how this connection forms in the developing infant. Iverson and Thelen (1999) proposed that the speech-gesture linkage emerges between 6-9 months, when rhythmic motor movements and babbling are at their peak; however, few published studies have tested the speech-gesture theory. A major purpose of the current study is to provide support for the Iverson and Thelen theory using longitudinal data; in addition, this study explores how posture and social context affect motor-vocal coordination. Fifteen infants were videotaped in their homes at 6, 7, 8, and 9 months, during which they either played alone or with their mothers. A series of 4 (Age) by 2 (Context) repeated-measures ANOVAs revealed no significant age-related increases in motor-vocal coordination. However, significant age-related increases in motor-vocal coordination were found when focusing on unilateral (single leg or arm) rhythmic movements coordinated with vocalizations. In addition, rhythmic motor movements were 4 times more likely to lead bouts of coordination than were vocalizations. Last, infants were more likely to show rhythmic motor movements and manual-vocal coordination bouts in the upright posture than in other postures. Results from this study show partial support for Iverson and Thelen’s model and extend findings from Iverson and Fagan (2004) by showing an important role for postural support of rhythmic motor activity.