Laser Doppler vibrometer and subminiature electret microphone: New methods for objective evaluation of nasality

Abstract

It is very important to evaluate nasality objectively in terms of both intersubject (severity of nasality) and intrasubject (validity of treatments, i.e., operation, speech therapy etc.). But there is no definite methodology for an objective evaluation of nasality. Our objectives were to evaluate the degree of nasality with a laser Doppler vibrometer (LDV) and a subminiature electret microphone (SEM) (using an accelerometer as a known standard), and to discuss the possibility of clinical use of these methodologies. LDV, used recently in the industrial field as well as in the medical/biological field, is a generator and detector of lasers to detect the velocity of the object’s vibration by the Doppler effect. The subjects were five healthy Japanese males (Tokyo dialect speakers). Used were sustained phonations (about 2 s) of /m/ and five Japanese vowels (/i/, /e/, /a/, /o/, /u/), and the Japanese words, shinkansen and shimbunshi (six repetitions for each phoneme). By both LDV and SEM systems, a significant difference was found beween /m/ and each vowel, which means that both systems can detect nasal/non-nasal differences and seem valid to evaluate the severity of pathological nasality (e.g., a cleft palate). Further study is planned for not only sustained phonation and word but also for sentence level, using patients (pathology) as well as healthy subjects (physiology). Furthermore, LDV seems to be a powerful tool for speech physiology where vibration of the body wall can be measured during speech and singing, without any contact receiver.