Ultrasonic time-motion records of lateral pharyngeal wall motion have previously been derived from the level of the angle of the mandible. In the present study a comparison is made between lateral pharyngeal wall displacements monitored at this level and displacements monitored at the level of velopharyngeal closure. Ultrasonic records were derived from both vocal tract levels in three normal adult speakers during utterances containing high and low vowels as well as nasal and nonnasal consonants. Mesial displacements of the lateral pharyngeal wall were greater at the superior monitoring site than at the level of the angle of the mandible. In addition, the displacement pattern was found to differ between the two sites. Low pharyngeal wall displacements followed a low vowel versus high vowel pattern, with greater displacements for low vowel phonations. In contrast, high pharyngeal wall displacements exhibited a nasal versus nonnasal character with greater lateral wall motion in a nonnasal environment. The results indicate the two levels of the pharynx are subject to different muscular forces.
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James A. Zagzebski (1975) studied this question.