ABSTRACT
OBJECTIVE: Dysphonia is a reduction in vocal quality that impacts communication and is often an early sign of a voice disorder. There is little information regarding the effects of auditory feedback control of loudness and pitch on voice quality. In this study, we used both loudness-shift and pitch-shift paradigms to study the relationship between auditory feedback control and vocal quality as measured by smoothed cepstral peak prominence (CPPS), which reflects the harmonicity of the voice signal. STUDY DESIGN: Experimental, mixed design. METHODS: We applied 200 ms loudness-shifts (± 0, 3, or 6 dB) and pitch-shifts (± 0, 50, and 100 cents) to auditory feedback during sustained vowel production in 25 healthy adults. We then measured CPPS before and after the loudness-shift or pitch-shift to investigate the effect of changes in auditory feedback on vocal harmonicity. RESULTS & CONCLUSIONS: Results showed that, on average, CPPS significantly decreased between the first half of the measured segment and the last half of the segment in the absence of auditory feedback shifts, suggesting that voice quality may be reduced across longer vowels over time. Upward and downward shifts in loudness auditory feedback caused a relative increase in CPPS, indicating an improvement in vocal harmonicity, even in cases when vocal intensity was reduced. Pitch alterations had inconsistent and minimal effects. We propose that there may be a control mechanism for voice quality that increases harmonicity of the voice signal to improve voice audibility (ie, ability to be heard) in the presence of unpredictable variability in voice intensity.
