Effects of velopharyngeal size, airflow rate, and microphone placement on nasalance score

Abstract

Nasometers are designed to measure the nasalance score, which is the ratio of nasal acoustic energy to total (nasal plus oral) acoustic energy during production of sonorant phonemes. However, nasometer microphones can detect hydrodynamic pressure changes in addition to acoustic pressure changes. This can occur when a talker with incomplete velopharyngeal closure leaks airflow through the nasal cavity; these nasal emissions lead to increased aerodynamic flow impinging on the nasal microphone, which may significantly increase the nasalance score. In order to quantify the influence of nasal emissions on the nasalance score, airflow with no voiced component was passed through an [s]-postured airway model based on a subject-specific geometry. Nasometer microphones measured pressure fluctuations exterior to the nose and mouth, from which the nasalance score was calculated. Flow rate, size of the velopharyngeal opening, and microphone position (medial or lateral) were varied in a factorial experiment. It was found that in the presence of nasal emissions, placing the nasometer microphones laterally decreases the nasalance score. Furthermore, the nasalance score generally increases with increased velopharyngeal opening size. These results indicate that hydrodynamic pressure from nasal emissions can increase the nasalance score and that this influence could be mitigated via microphone placement.