Relative fundamental frequency as an acoustic correlate of vocal effort in spasmodic dysphonia.

Abstract

Individuals with vocal hyperfunction have lowered relative fundamental frequency (RFF) in vowels immediately preceding and following a voiceless consonant, but the relationship between RFF and perceived voice quality has yet to be studied in neurogenic voice disorders. The purpose of this study was to determine the relationship between RFF with listeners’ perceptions of 19 individuals with adductor spasmodic dysphonia. Speech recordings were presented to 20 inexperienced listeners who evaluated effort and overall severity using visual analog scales. The correlation coefficient (R2) between average effort and severity measures and an RFF measure was calculated as a function of the number of acoustic instances used for the RFF estimate (1–9, of a total of nine voiced-voiceless-voiced instances). Increases in the number of acoustic instances used for the RFF average led to increases in the correlation with perceptual measures, with use of six or more instances resulting in a stable estimate. Correlation coefficient values were highest between effort and RFF (range R2=0.06–0.43), with slightly lower correlation coefficients between severity and RFF (range R2=0.06–0.35). This study indicates that RFF measures are correlated with perceived voice quality and that guidelines should be developed for calculating reliable estimates of RFF in future research.