Modeling anomalous vocal tracts for investigating vowel production

Abstract

Apert and Crouzon syndromes involve head and neck malformations affecting vocal‐tract architecture through midface hypoplasia, malocclusion, reduction in pharyngeal depth, anomalous velar, and palatal configurations. Acoustic data on vowels from Apert and Crouzon speech are correlated with results from computer simulations of vowel production [Henke, Hosein] which convert information on physical measures from the speakers' articulations into values for a series of transfer functions. These investigations help determine consequences to vowel production resulting from these malformations. We focus first on [u]: (1) acoustic analysis reveals [u] to have the poorest relationship to reported normal formant values, (2) normal [u] articulation requires expansion of oral and pharyngeal cavities—difficult for these subjects. Physical measures were determined from midsaggital [u] and frontal cephalograms, dental casts and patient photographs. Successive alterations were made to the model to achieve convergence with known acoustic output. Current findings indicate: (1) a significantly compressed vowel space for these speakers, (2) little relationship between oral cavity volume and [u] formant structure, (3) strong relationship between pharyngeal volume, lip aperture, and oral/pharyngeal constriction for the first two formants.