Voice focus & audio–vocal feedback in phonation (Lee & Lee, 2024)

Purpose: This study investigates the effect of voice-focus adjustments on oronasal balance and auditory feedback control of speech via analyzing spectral distribution, perceived loudness, and nasal vibrations during sustained phonation and passage reading.

Method: Twenty-five speech-language pathologists sustained /a/ and read passages with forward, backward, and natural voice focuses in quiet and noisy conditions. The low-frequency power (LFP) below 3 Hz of vocal fundamental frequency was analyzed to access audio–vocal feedback control. Long-term average spectra of speech were converted to phon spectra based on equal-loudness contours ISO 226:2003 to estimate perceived loudness of self-voice across different conditions. Nasal vibrations were also recorded using a digital accelerometer to measure oronasal coupling.

Results: Forward-focused voice enhanced the nasal acceleration and reduced LFP, suggesting that increasing the degree of oronasal coupling can improve audio–vocal feedback control compared to natural and backward-focused voices. Voice-focus adjustments were most related to average power and phon values in the 0.2- to 0.3-kHz band. In noise, perceived loudness in the 0.5- to 2.3-kHz band effectively predicted LFP, outperforming the average spectral power of the same band.

Conclusions: Voice-focus adjustments significantly impact both the acoustic transfer function of the vocal tract and the spontaneous fine-tuning of audio–vocal integration. This influence becomes particularly pronounced when sound intensity or perceived loudness is changed within the frequency range of 0.2–2.3 kHz, depending on the voice focus selected by the speakers.

Supplemental Material S1. Examples of power spectra of F0s in a frequency range from 0.2 Hz to 25 Hz for sustained /a/ productions with (A) natural voice (NF), (B) forward-focused voice (FF), and (C) backward-focused voice (BF). N0, natural auditory condition. N90, 90-dBC noise exposure.

Lee, S.-H., & Lee, G.-S. (2024). Influence of voice focus on auditory feedback control of speech using long-term average spectrum, phon spectrum, and accelerometry. Journal of Speech, Language, and Hearing Research, 67(12), 4598–4613. https://doi.org/10.1044/2024_JSLHR-24-00051