PREDICTION OF MODELED VELOPHARYNGEAL ORIFICE AREAS USING HYDROKINETIC PRINCIPLES DURING AERODYNAMIC SIMULATION OF VOICELESS STOP CONSONANTS

BONNIE ELLEN SMITH, Purdue University

Abstract

Warren and his colleagues described a non-invasive method for calculating velopharyngeal orifice area over a decade ago (Warren and DuBois, 1964; Warren and Ryon, 1967; Warren, 1975). A small number of investigators have assessed the accuracy of modeled orifice areas calculated using this equation (Warren and DuBois, 1964; Lubker, 1969; Smith and Weinberg, 1980; Horii and Lang, 1981). The results of these projects have led to divergent views about the accuracy of modeled orifice area estimates obtained on the basis of hydrokinetic principles. In addition, the preliminary results of a project undertaken by this author indicated that there was extensive variability among calculated orifice areas obtained under conditions in which velopharyngeal incompetence was induced in normal-speaking, adult talkers. Taken together, these findings highlighted the need to specify the predictive nature of the hydrokinetic equation under conditions like those found during speech production. The overall aim of the project was to quantify the predictive nature of modeled velopharyngeal orifice area calculations obtained using the hydrokinetic equation under conditions simulating voiceless, stop consonant production. Two major predictions were advanced: (1) that orifice area estimates made during steady flow conditions and during alternating flow conditions at loci where flow rate is not changing should be highly accurate and comparable and (2) that orifice estimates made during alternating flow conditions at loci where flow is changing should be less accurate. These predictions are based on theoretical considerations which indicate that the hydrokinetic equation is suggested by physical equations for steady, ideal fluid flow motion (Shapiro, 1953; Warren and DuBois, 1964). To assess the accuracy of these predictions, a series of modeling experiments were completed. Specifically, a vocal tract model was driven in a steady-state fashion and also in a dynamic fashion to simulate voiceless, stop consonant production. The velopharyngeal orifice of the model was open to varying degrees during these experiments. The results of this project revealed that the average calculated orifice areas corresponded favorably with orifice openings known to be present in the model and that variation in predicted orifice areas was small. The average errors in predicted areas calculated at locations where flow rate was not changing were four to six per cent, while the average error in the area estimation obtained from measurements made at locations where flow rate was changing was about 11 per cent. It was established that acceleration effects are present in dynamic modeling data and that the presence of such effects does occasion variation in orifice area estimation. Despite this fact, it has been shown that these effects can be minimized. The hydrokinetic equation proposed by Warren can be used to obtain accurate estimates of modeled velopharyngeal orifice areas during conditions simulating voiceless, stop consonant production when such estimates are made at airflow peak loci. In view of these findings, a protocol for aerodynamic assessment of velopharyngeal function is offered, and several logical extensions of the present project are suggested.

Degree

Ph.D.

Subject Area

Speech therapy

COinS