Theory and Instrumentation for Quantitative Measurement for Nasality

Abstract

Speech is recognized as the essential criterion for assessing the ultimate results of treatment for children born with clefts of the palate. In spite of this fact, the precision with which speech and underlying oral function may be assessed has developed rather slowly. The main limitation in progress seems to have been that essentially all diagnostic and remedial approaches have depended upon perceptual evaluation as the basis for clinical judgments. This approach has at least two major limitations. First, the standard baselines against which judgments are made are non-stable and thus rather undependable for repeated comparisons over time, or comparisons among different clients. Second, the process of sharing information among clinicians is hampered by the vagueness with which the basic parameters of disability are defined. Thus, the focus of attention has tended to shift. to known parameters, such as speech artic-ulation, which can be classified more reliably, rather than to nasality which is more continuously variable and therefore less easily managed by perceptual judgment. The rapid evolution of electronic technology has made new biomeas— urement procedures feasible for more precise, quantitative, and reliable measurement of nasality in persons with operated clefts of the palate. The present paper summarizes the results of a project to develop an instrument for this purpose. The feasibility of this electronic instrumen— tation designed to measure acoustic characteristics beyond the compar— ative intensity of sound emitted from the mouth and nose was suggested in 1961 through use of a dual-channel electrophonocardiograph with some capability for frequency selectivity. Formal work to fabricate the presently described instrumentation was begun in 1966. Acoustic Theory Three aspects of acoustic theory pertaining to assessment of distortion from nasality are fundamental to electronic instrumentation ap