Human vocal tract growth: a longitudinal study of the development of various anatomical structures

The growth of the head and neck and its components, including that of the vocal tract, is not homothetic but appears rather as an anamorphosis. The growth of various structures presents a phenomenon of heterochrony. Another important issue in vocal tract growth is sexual dimorphism. It was first claimed that sexual dimorphism appears at puberty, but a recent study has suggested that some prepubertal differences exist. To study these two phenomena, we used longitudinal radiographic data of sixty-eight typical subjects (966 radiographs, taken from 1 month to 25 years) and twelve fetuses (anatomical sections). In this study, we analyzed the growth curves and growth types of the hard and soft palate, the pharyngeal cavity and the estimated length of the whole vocal tract using non-linear mixedeffect models, in order to take advantage of our unique longitudinal dataset. Results indicate that most of the structures follow a neural/somatic growth type, while the pharyngeal cavity follows a more somatic growth type. As concerns sexual dimorphism, no prepubertal differences were found, suggesting that the sexual dimorphism is likely to begin at puberty. These results have implications for the acoustics of speech production during development and should lead to improvements in vocal tract growth modeling.