Long-term Average Spectrum and Nasal Accelerometry in Sentences of Differing Nasality and Forward-Focused Vowel Productions Under Altered Auditory Feedback.

OBJECTIVES AND BACKGROUND: To investigate whether voice focus adjustments can alter the audio-vocal feedback and consequently modulate speech/voice motor control. Speaking with a forward-focused voice was expected to enhance audio-vocal feedback and thus decrease the variability of vocal fundamental frequency (F0). MATERIALS AND METHOD: Twenty-two healthy, untrained adults (10 males and 12 females) were requested to sustain vowel /a/ with their natural focus and a forward focus and to naturally read the nasal, oral, and mixed oral-nasal sentences in normal noise-masked auditory conditions. Meanwhile, a miniature accelerometer was externally attached on the noise to detect the nasal vibrations during vocalization. Audio recordings were made and analyzed using the long-term average spectrum (LTAS) and power spectral analysis of F0. RESULTS: Compared with naturally-focused vowel production and oral sentences, forward-focused vowel productions and nasal sentences both showed significant increases in nasal accelerometric amplitude and the spectral power within the range of 200∼300 Hz, and significantly decreased the F0 variability below 3 Hz, which has been reported to be associated with enhanced auditory feedback in our previous research. The auditory masking not only significantly increased the low-frequency F0 variability, but also significantly decreased the ratio of the spectral power within 200∼300 Hz to the power within 300∼1000 Hz for the vowel and sentence productions. Gender differences were found in the correlations between the degree of nasal coupling and F0 stability as well as in the LTAS characteristics in response to noise. CONCLUSIONS: Variations in nasal-oral acoustic coupling not only change the formant features of speech signals, but involuntarily influence the auditory feedback control of vocal fold vibrations. Speakers tend to show improved F0 stability in response to a forward-focused voice adjustment.

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 enhance the auditory feedback of the speaker's own voice and, thus, reduce the variability of f o during sustained phonation, especially when vocalizing in the high noise condition.

Vocal fold nodules: A disorder of phonation organs or auditory feedback?

OBJECTIVE: Increasing evidence supports that auditory feedback of one's own voice closely relates to real-time adjustments of vocal control. Previous studies highlighted that the low-frequency modulations of below 3 Hz (LFM) embedded in vocal fundamental frequency (F0) showed a reflex-like response to altered auditory inputs. However, the auditory feedback control of different vocal disorders remains unclear. DESIGN: A cross-sectional, case-controlled study. SETTING: A tertiary medical centre. PARTICIPANTS: Sustained vocalisations of vowel/a/ from adult healthy controls and patients with vocal fold nodules, vocal fold polyps and vocal fold cysts, respectively. The vocalisations were made at a comfortable pitch and at the intensity of 70 ~ 80 dBC under the following four auditory conditions: natural hearing, 90-dBC speech noise, 10-dBC enhanced feedback of self-produced voice and both the noise and voice feedback. MAIN OUTCOME MEASURES: Power spectral analysis of F0 contour of sustained vowel. RESULTS: Patients with vocal fold nodules presented with different audio-vocal feedback behaviour and audio-vocal response to speech noise from the other two vocal pathologies of vocal fold polyp and vocal fold cyst as well as the healthy controls (P < .001, one-way ANOVA). CONCLUSION: The vocal fold nodules may be not only a vocal fold disease but also a disease caused by abnormal audio-vocal feedback. Moreover, the distinct audio-vocal feedback of vocal fold nodules could be revealed by power spectral analysis of vocal fundamental frequencies. Although further investigations are necessary, adjustments of audio-vocal feedback behaviour may provide a new insight and benefit to the treatment of vocal fold nodules in the future.

Responses of Middle-Frequency Modulations in Vocal Fundamental Frequency to Different Vocal Intensities and Auditory Feedback.

OBJECTIVES AND BACKGROUND: Auditory feedback can make reflexive responses on sustained vocalizations. Among them, the middle-frequency power of F0 (MFP) may provide a sensitive index to access the subtle changes in different auditory feedback conditions. MATERIALS AND METHODS: Phonatory airflow temperature was obtained from 20 healthy adults at two vocal intensity ranges under four auditory feedback conditions: (1) natural auditory feedback (NO); (2) binaural speech noise masking (SN); (3) bone-conducted feedback of self-generated voice (BAF); and (4) SN and BAF simultaneously. The modulations of F0 in low-frequency (0.2 Hz-3 Hz), middle-frequency (3 Hz-8 Hz), and high-frequency (8 Hz-25 Hz) bands were acquired using power spectral analysis of F0. Acoustic and aerodynamic analyses were used to acquire vocal intensity, maximum phonation time (MPT), phonatory airflow, and MFP-based vocal efficiency (MBVE). RESULTS: SN and high vocal intensity decreased MFP and raised MBVE and MPT significantly. BAF showed no effect on MFP but significantly lowered MBVE. Moreover, BAF significantly increased the perception of voice feedback and the sensation of vocal effort. CONCLUSIONS: Altered auditory feedback significantly changed the middle-frequency modulations of F0. MFP and MBVE could well detect these subtle responses of audio-vocal feedback.

Relationships Between Formant Frequencies of Sustained Vowels and Tongue Contours Measured by Ultrasonography.

PURPOSE: The purpose of this study was to explore the formant-articulation relationships in corner vowels by acoustic analysis of speech signals and measuring tongue contour using ultrasonography. METHOD: Eighteen healthy adults (8 men, 10 women), aged between 20 and 40 years, were enrolled. Speech signals of sustained vowels /ɑ/, /i/, and /u/ were recorded to obtain the first 2 formant frequencies. Tongue height, tongue advancement, and lengths of posterior tongue surface (LPTS) and anterior oral cavity (LAOC) were obtained using ultrasound image processing technique in order to examine the resonance mechanism of the oral vocal tract. RESULTS: LPTS and LAOC, as well as mean frequencies of the first and second formants, showed significant differences between sexes and among vowels. The first formant significantly and better correlated with LPTS than with tongue height (r = -.78, p < .001, Pearson's correlation). The correlation of the second formant with LAOC (r = -.85, p < .001) was also significant and better than the correlation with tongue advancement. Sex, however, did not show significant correlation with the formant frequencies. CONCLUSIONS: Ultrasonographic measurements of tongue contour correlated well to the formant frequencies. The results stressed the importance of tongue shaping in articulation. Although more studies are necessary in clinical implications, disorders associated with abnormal tongue shaping may be the target applications in the future.

Audio-vocal responses of vocal fundamental frequency and formant during sustained vowel vocalizations in different noises.

Sustained vocalizations of vowels [a], [i], and syllable [mə] were collected in twenty normal-hearing individuals. On vocalizations, five conditions of different audio-vocal feedback were introduced separately to the speakers including no masking, wearing supra-aural headphones only, speech-noise masking, high-pass noise masking, and broad-band-noise masking. Power spectral analysis of vocal fundamental frequency (F0) was used to evaluate the modulations of F0 and linear-predictive-coding was used to acquire first two formants. The results showed that while the formant frequencies were not significantly shifted, low-frequency modulations (<3 Hz) of F0 significantly increased with reduced audio-vocal feedback across speech sounds and were significantly correlated with auditory awareness of speakers' own voices. For sustained speech production, the motor speech controls on F0 may depend on a feedback mechanism while articulation should rely more on a feedforward mechanism. Power spectral analysis of F0 might be applied to evaluate audio-vocal control for various hearing and neurological disorders in the future.

Effects of hearing aid amplification on voice F0 variability in speakers with prelingual hearing loss.

To investigate the audio-vocal feedback responses of (F0) to hearing amplification in severe-to-profound prelingual hearing loss (SPHL) using power spectral analysis of F0 contour of sustained vowels. Sustained phonations of vowel/a/of seventeen participants with SPHL were acquired with and without hearing-aid amplifications. The vocal intensity was visually fed back to the participants to help controlling the vocal intensity at 65-75 dBA and 85-95 dBA. The F0 contour of the phonations was extracted and submitted to spectral analysis to measure the extent of F0 fluctuations at different frequency ranges. The results showed that both high vocal intensity and hearing-aid amplification significantly improved voice F0 control by reducing the low-frequency fluctuations (low-frequency power, LFP, 0.2-3 Hz) in F0 spectrum. However, the enhanced feedback from higher vocal intensity and/or hearing amplification was not adequate to reduce the LFP to the level of a normal hearing person. Moreover, we found significant and negative correlations between LFP and supra-threshold feedback intensity (phonation intensity - hearing threshold level) for the frequencies of 500-2000 Hz. Increased vocal intensity, as well as hearing-aid amplification, improved voice F0 control by reducing the LFP of F0 spectrum, and the subtle changes in voices could be well explored using spectral analysis of F0.