Characterization of mandibular movement during speech in the presence of oral articulatory perturbation.

Objective: Mandibular movement is essential for speech, swallowing, and mastication. The purpose of this study was to test the hypothesis that altering oral cavity geometry would result in an increased vertical and more posterior jaw displacement during speech.
Design: Twelve English speaking female adult dentate volunteers, age range 21-31 (mean ± SD age, 25.3 ± 2.2 years) participated in this prospective crossover study. Compensatory jaw movement was measured during pronunciation of the sound "s" in three vowel contexts (/i/, /a/, /u/). An acrylic palatal device was used to perturb the oral cavity in anterior and posterior palate. Speech was recorded under five conditions; no device, device, device after 15 min, device after 2 weeks, after removal of the device. The vertical, horizontal, and lateral mandibular movement was recorded. A Within-Subject 2-Factorial Repeated Measures ANOVA was performed to evaluate the statistical significance (p ≤ 0.05).
Results: The repeated measures for the mean vertical displacement revealed a main effect for the condition [F (6.970), p=.001], and the device [F (13.634), p=.001]. For horizontal displacement there was a main effect for the condition [F (6.970), p=.001], and the device [F (13.634), p=.001]. For lateral displacement there was a main effect for the device [F (3.790), p=.051].
Conclusions: Our study demonstrated that during the pronunciation of "s" the jaw position is extremely stable, even when the oral cavity geometry is altered. Therefore, compensation for the perturbation occurs using other speech articulators such as the tongue.
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