MEASURES OF VOCAL FUNCTION DURING CHANGES IN VOCAL EFFORT LEVEL

The purpose of this article is to present the results of a controlled study of the day-to-day variabilities of three acoustic parameters (ji tter, shimmer, and normalized noise energy), and two electroglottograp hic parameters (contact quotient and contact quotient perturbation) fo r vowels produced at three vocal efforts (low, normal, high). Data wer e obtained with use of a sophisticated bilinear interpolation pitch de tection method. A repeated measures design required subjects to produc e the vowels /ae/ and /a/ five times a day over 3 days at each vocal e ffort level. The jitter, shimmer, and normalized noise energy values f rom acoustic measures and contact quotient and contact quotient pertur bation values varied significantly among the three vocal effort levels , The clinical implication of this finding is that vocal effort must b e controlled in order to obtain consistent clinical measures. Furtherm ore, day-to-day variability must be taken into account if representati ve measures are to be obtained for clinical use.