Influence of Voice Focus on Auditory Feedback Control of Speech Using Long-Term Average Spectrum, Phon Spectrum, and Accelerometry

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.