Contributions of Forward-Focused Voice to Audio-Vocal Feedback Measured Using Nasal Accelerometry and Power Spectral Analysis of Vocal Fundamental Frequency

Purpose: The spectral powers of the modulations of vocal fundamental frequency (f_o) less than 3 Hz (low-frequency power, LFP) and between 3 and 8 Hz (middle-frequency power, MFP) had been established to indicate the audio-vocal feedback status and vocal efficiency of a speaker, and a resonant voice may enhance the auditory-vocal feedback. This study aims to determine whether the auditory feedback can be augmented by a forward and resonant voice and therefore contribute to the modulations of f_o variability. Method: Vocal signals and accelerometric signals of lateral nasal cartilage were obtained from 27 healthy adults who, respectively, sustained vowels/a/ and/i/ with their habitual speaking voice and with a forward-focused voice under three auditory conditions: natural hearing (N0), high-level noise exposure (N90), and low-level noise exposure (N60). Nasal skin vibrations were measured using a nasal accelerometry to reflect voice resonance status. Vocal intensity and f_o variability were also analyzed to show the auditory-vocal interactions under varied conditions of auditory feedback and voice resonance. Results: In both N0 and N90 conditions, forward-focused voice showed a significantly lower LFP than the speakers’ habitual voice. In addition, LFP of f_o would significantly increase during natural voice production as the voice feedback was greatly masked by high-intensity noise; however, with a forward-focused voice, the noise-induced variation in LFP was significantly decreased. Under N90, MFP significantly decreased during forward-focused voice production compared with that measured during natural voice production. The stability of f_o modulations was not adversely affected by N60. Conclusion: The results support the idea that vocalizing with a forward-focused voice enhances the auditory feedback of the speaker’s own voice and, thus, reduces the variability of f_o during sustained phonation, especially when vocalizing in the high noise condition.