Lip shape in adult talkers is primarily driven by vertical opening; however, little is known about how children converge on this highly organized and efficient lip shape pattern. This longitudinal study investigated the development of lip shape control and its relation to speech and vocabulary acquisition in 28 typically developing children between 3 months and 5 years of age. Results suggested that during infancy lip shape was characterized by horizontal spreading of the lips, but that the contribution of vertical opening increased nonmonotonically over time. This change co-occurred with gains in expressive communication. These data suggest that lip shape may represent an important marker of normal oromotor development. Future work is required to determine the functional significance of the observed changes in lip shape control for identifying children at risk for speech and language impairments.
Jenya Iuzzini-Seigel is at Marquette University. Tiffany P. Hogan, Panying Rong, and Jordan R. Green are with the Department of Communication sciences and Disorders at MGH IHP, Boston MA.