The role of auditory feedback in sustaining vocal vibrato

Modifications of auditory feedback and its effects on the voice of adult subjects: a scoping review

INTRODUCTION

The auditory perception of voice and its production involve auditory feedback, kinesthetic cues and the feedforward system that produce different effects for the voice. The Lombard, Sidetone and Pitch-Shift-Reflex effects are the most studied. The mapping of scientific experiments on changes in auditory feedback for voice motor control makes it possible to examine the existing literature on the phenomenon and may contribute to voice training or therapies.

PURPOSE

To map experiments and research results with manipulation of auditory feedback for voice motor control in adults.

METHOD

Scope review following the Checklist Preferred Reporting Items for Systematic reviews and Meta-Analyses extension (PRISMA-ScR) to answer the question: "What are the investigation methods and main research findings on the manipulation of auditory feedback in voice self-monitoring of adults?". The search protocol was based on the Population, Concept, and Context (PCC) mnemonic strategy, in which the population is adult individuals, the concept is the manipulation of auditory feedback and the context is on motor voice control. Articles were searched in the databases: BVS/Virtual Health Library, MEDLINE/Medical Literature Analysis and Retrieval System online, COCHRANE, CINAHL/Cumulative Index to Nursing and Allied Health Literature, SCOPUS and WEB OF SCIENCE.

RESULTS

60 articles were found, 19 on the Lombard Effect, 25 on the Pitch-shift-reflex effect, 12 on the Sidetone effect and four on the Sidetone/Lombard effect. The studies are in agreement that the insertion of a noise that masks the auditory feedback causes an increase in the individual's speech intensity and that the amplification of the auditory feedback promotes the reduction of the sound pressure level in the voice production. A reflex response to the change in pitch is observed in the auditory feedback, however, with particular characteristics in each study.

CONCLUSION

The material and method of the experiments are different, there are no standardizations in the tasks, the samples are varied and often reduced. The methodological diversity makes it difficult to generalize the results. The main findings of research on auditory feedback on voice motor control confirm that in the suppression of auditory feedback, the individual tends to increase the intensity of the voice. In auditory feedback amplification, the individual decreases the intensity and has greater control over the fundamental frequency, and in frequency manipulations, the individual tends to correct the manipulation. The few studies with dysphonic individuals show that they behave differently from non-dysphonic individuals.

High and Wide: An In Silico Investigation of Frequency, Intensity, and Vibrato Effects on Widely Applied Acoustic Voice Perturbation and Noise Measures

OBJECTIVES

This in silico study explored the effects of a wide range of fundamental frequency (fo), source-spectrum tilt (SST), and vibrato extent (VE) on commonly used frequency and amplitude perturbation and noise measures.

METHOD

Using 53 synthesized tones produced in Madde, the effects of stepwise increases in fo, intensity (modeled by decreasing SST), and VE on the PRAAT parameters jitter % (local), relative average perturbation (RAP) %, shimmer % (local), amplitude perturbation quotient 3 (APQ3) %, and harmonics-to-noise ratio (HNR) dB were investigated. A secondary experiment was conducted to determine whether any fo effects on jitter, RAP, shimmer, APQ3, and HNR were stable. A total of 10 sinewaves were synthesized in Sopran from 100 to 1000 Hz using formant frequencies for /a/, /i/, and /u/-like vowels, respectively. All effects were statistically assessed with Kendall's tau-b and partial correlation.

RESULTS

Increasing fo resulted in an overall increase in jitter, RAP, shimmer, and APQ3 values, respectively (P < 0.01). Oscillations of the data across the explored fo range were observed in all measurement outputs. In the Sopran tests, the oscillatory pattern seen in the Madde fo condition remained and showed differences between vowel conditions. Increasing intensity (decreasing SST) led to reduced pitch and amplitude perturbation and HNR (P < 0.05). Increasing VE led to lower HNR and an almost linear increase of all other measures (P < 0.05).

CONCLUSION

These novel data offer a controlled demonstration for the behavior of jitter (local) %, RAP %, shimmer (local) %, APQ3 %, and HNR (dB) when varying fo, SST, and VE in synthesized tones. Since humans will vary in all of these aspects in spoken language and vowel phonation, researchers should take potential resonance-harmonics type effects into account when comparing intersubject or preintervention and postintervention data using these measures.

Vocal Vibrato Characteristics in Historical and Contemporary Opera, Operetta, and Schlager

OBJECTIVES/HYPOTHESIS

Vibrato is a core aesthetic element in singing. It varies considerably by both genre and era. Though studied extensively in Western classical singing over the years, there is a dearth of studies on vibrato in contemporary commercial music. In addressing this research gap, the objective of this study was to find and investigate common crossover song material from the opera, operetta, and Schlager singing styles from the historical early 20th to the contemporary 21st century epochs.

STUDY DESIGN/METHODS

A total of 51 commercial recordings of two songs, "Es muss was Wunderbares sein" by Ralph Benatzky, and "Die ganze Welt ist himmelblau" by Robert Stolz, from "The White Horse Inn" ("Im weißen Rößl") were collected from opera, operetta, and Schlager singers. Each sample was annotated using Praat and analyzed in a custom Matlab- and Python-based algorithmic approach of singing voice separation and sine wave fitting novel to vibrato research.

RESULTS

With respect to vibrato rate and extent, the three most notable findings were that (1) f_o and vibrato were inherently connected; (2) Schlager, as a historical aesthetic category, has unique vibrato characteristics, with higher overall rate and lower overall extent; and (3) f_o and vibrato extent varied over time based on the historical or contemporary recording year for each genre.

CONCLUSIONS

Though these results should be interpreted with caution due to the limited sample size, conducting such acoustical analysis is relevant for voice pedagogy. This study sheds light on the complexity of vocal vibrato production physiology and acoustics while providing insight into various aesthetic choices when performing music of different genres and stylistic time periods. In the age of crossover singing training and commercially available recordings, this investigation reveals important distinctions regarding vocal vibrato across genres and eras that bear beneficial implications for singers and teachers of singing.

Assessing Acoustic Parameters in Early Music and Romantic Operatic Singing

OBJECTIVE

Since the recent early music (EM) revival, a subset of singers have begun to specialize in a style of singing that is perceptually different from the more "mainstream" romantic operatic (RO) singing style. The aim of this study is to characterize EM with respect to RO singing in terms of its vibrato characteristics and the singer's formant cluster.

STUDY DESIGN

This study presents a within-subject experimental design.

METHODS

Ten professional singers (5 F; 5M) versed in both EM and RO repertoire were enrolled in the study. Each singer recorded the first 10 bars of the famous Aria, "Amarilli Mia Bella" (Giulio Caccini, 1602) a cappella, in RO and EM styles, in random order. Three sustained notes were extracted from the acoustical recordings and were analyzed using the free user-friendly software Biovoice to extract five parameters: vibrato rate, vibrato extent, vibrato jitter (J_vib), vibrato shimmer, and quality ratio (QR), an estimation of the singer's formant power.

RESULTS

Vibrato in EM singing was characterized by a higher rate, a smaller extent, and less regular cycle-cycle period duration (higher J_vib) compared to RO singing. As in previous studies, RO singing presented a more prominent singer's formant, as indicated by a smaller QR.

CONCLUSIONS

Acoustical analysis of some vibrato characteristics and the Singer's Formant significantly differentiated EM from RO singing styles. Given the acoustical distinctions between EM and RO styles, future scientific and musicological studies should consider distinguishing between the two styles rather than using a singular term for and description of Western Classical singing.

Auditory-Motor Control of Fundamental Frequency in Vocal Vibrato

PURPOSE

The purpose of this study was to investigate how classically trained singers use their auditory feedback to control fundamental frequency (fo) during production of vocal vibrato. Two main questions were addressed: (1) Do singers produce reflexive foresponses to sudden perturbation of the fo of their auditory feedback during production of vibrato indicative of feedback control? (2) Do singers produce adaptive foresponses to repeated perturbation of the fo of their auditory feedback during production of vibrato indicative of feedback and feedforward control? In addition, one methodological question was addressed to determine if adaptive fo responses were more precisely assessed with or without an auditory cue for fo during the repeated fo perturbation paradigm.

METHOD

Ten classically trained singers produced sustained vowels with vibrato while the fo and harmonics of their auditory feedback were suddenly perturbed by 100 cents to assess reflexive control or repeatedly perturbed by 100 cents to assess adaptive control. Half of the participants completed the repeated perturbation experiment with an auditory cue for fo, and the other half completed the experiment without an auditory cue for fo. Acoustical analyses measured changes in mean fo in response to the auditory feedback perturbations.

RESULTS

On average, participants produced compensatory responses to both sudden and repeated perturbation of the fo of their auditory feedback. The magnitude of the responses to repeated perturbations was larger than the responses to sudden perturbations. Responses were also larger in the cued, repeated fo perturbation experiment than in the uncued, repeated fo perturbation experiment.

CONCLUSIONS

These findings indicate that classically-trained singers use both feedforward and feedback mechanisms to control their average fo during production of vibrato. When compared to prior studies of singers producing a steady voice, the reflexive fo responses were larger in the current study, which may indicate that the feedback control system is engaged more during production of vibrato.

The Effects of Masked and Delayed Auditory Feedback on Fundamental Frequency Modulation in Vocal Vibrato

PURPOSE

Although relatively precise control over the extent and rate of fundamental frequency (fo) modulation may be needed for optimal production of vibrato, the role of auditory feedback in controlling vibrato is not well understood. Previous studies altered the gain and timing of auditory feedback in singers producing vibrato and showed inconsistent effects on the extent and rate of fo modulation, which may have been related to small sample sizes or limited analyses. Therefore, the purpose of this study was to further investigate whether the gain or timing of auditory feedback impacts control of vibrato in a larger sample of speakers and with advanced statistical analyses.

METHOD

Ten classically-trained singers produced sustained vowels with vibrato while their auditory feedback was masked with pink noise or multi-talker babble to reduce the gain of their auditory feedback and while their auditory feedback was delayed by about 200 or 300 milliseconds to alter the timing of their auditory feedback. Acoustical analyses measured changes in the extent and rate of fo modulation in the masked and delayed trials relative to control trials. Bayesian modeling was used to analyze the effects of noise-masked, babble-masked, and delayed auditory feedback on the extent and rate of fo modulation.

RESULTS

There was compelling evidence that noise masking increased the extent of fo modulation, and babble masking increased the variability in the rate of fo modulation (ie, jitter of fo modulation). Masked auditory feedback did not affect the average rate of fo modulation. Delayed auditory feedback did not affect the extent, rate, or jitter of fo modulation.

CONCLUSIONS

The current study demonstrated that reducing the gain of the auditory feedback with noise masking increased the extent of fo modulation but did not affect the average rate of fo modulation in classically-trained singers producing vibrato. Reducing the gain of the auditory feedback with babble masking and altering the timing of auditory feedback with imposed delays did not affect the average extent or rate of fo modulation. However, babble masking increased the jitter of fo modulation rate, which suggests that modulated auditory feedback may affect the periodicity of fo modulation from one modulation cycle to the next. These findings clarify the role of auditory feedback in controlling vibrato and may inform the current reflex-resonance models of vibrato.

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.

Intermittent theta burst stimulation over right somatosensory larynx cortex enhances vocal pitch-regulation in nonsingers

While the significance of auditory cortical regions for the development and maintenance of speech motor coordination is well established, the contribution of somatosensory brain areas to learned vocalizations such as singing is less well understood. To address these mechanisms, we applied intermittent theta burst stimulation (iTBS), a facilitatory repetitive transcranial magnetic stimulation (rTMS) protocol, over right somatosensory larynx cortex (S1) and a nonvocal dorsal S1 control area in participants without singing experience. A pitch-matching singing task was performed before and after iTBS to assess corresponding effects on vocal pitch regulation. When participants could monitor auditory feedback from their own voice during singing (Experiment I), no difference in pitch-matching performance was found between iTBS sessions. However, when auditory feedback was masked with noise (Experiment II), only larynx-S1 iTBS enhanced pitch accuracy (50-250 ms after sound onset) and pitch stability (>250 ms after sound onset until the end). Results indicate that somatosensory feedback plays a dominant role in vocal pitch regulation when acoustic feedback is masked. The acoustic changes moreover suggest that right larynx-S1 stimulation affected the preparation and involuntary regulation of vocal pitch accuracy, and that kinesthetic-proprioceptive processes play a role in the voluntary control of pitch stability in nonsingers. Together, these data provide evidence for a causal involvement of right larynx-S1 in vocal pitch regulation during singing.

Delay-induced low-frequency modulation of the voice during sustained phonation

An important property of negative feedback systems is the tendency to oscillate when feedback is delayed. This paper evaluated this phenomenon in a sustained phonation task, where subjects prolonged a vowel with 0-600 ms delays in auditory feedback. This resulted in a delay-dependent vocal wow: from 0.4 to 1 Hz fluctuations in fundamental frequency and intensity that increased in period and amplitude as the delay increased. A similar modulation in low-frequency oscillations was not observed in the first two formant frequencies, although some subjects did display increased variability. Results suggest that delayed auditory feedback enhances an existing periodic fluctuation in the voice, with a more complex, possibly indirect, influence on supraglottal articulation. These findings have important implications for understanding how speech may be affected by artificially applied or disease-based delays in sensory feedback.

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.

Principal component analysis reveals differential attentional modulation of the vocal response to pitch perturbation

The auditory-vocal system modifies voice fundamental frequency (F0) with auditory feedback. The responses to F0 changes in auditory feedback are known to depend on the task. The hypothesis explored in this study is that the task dependency is the result of multiple components of the F0 responses differently modulated with different tasks. Attention to audition was manipulated by task condition by the instruction to ignore or to count the number of the F0 shifts heard during vocalization. A synthetic voice with pitch shifts was used as auditory pseudo-feedback. The upward and downward shifts evoked very similar vocal F0 response patterns with polarity reversal. Attention to the auditory feedback caused a reduction in the grand-average response amplitude. By decomposing the F0 responses with principal component analysis (PCA), three principal components (PCs) with different peak latencies were found to have contributions above the criterion of 5%, totaling to 74%. All three PCs contributed to a compensatory response under the "ignore" condition. The slowest PC changed its polarity and the intermediate PC was reduced to almost zero under the "count" condition. Thus, the task-dependency of the F0 response to auditory feedback can be described in terms of different sensitivities of components to attention.

Sensory attenuation of self-produced feedback: the Lombard effect revisited

The Lombard effect describes the automatic and involuntary increase in vocal intensity that speakers exhibit in a noisy environment. Previous studies of the Lombard effect have typically focused on the relationship between speaking and hearing. Automatic and involuntary increases in motor output have also been noted in studies of finger force production, an effect attributed to mechanisms of sensory attenuation. The present study tested the hypothesis that sensory attenuation mechanisms also underlie expression of the Lombard effect. Participants vocalized phonemes in time with a metronome, while auditory and visual feedback of their performance were manipulated or removed during the course of the trial. We demonstrate that providing a visual reference to calibrate somatosensory-based judgments of current vocal intensity resulted in reduced expression of the Lombard effect. Our results suggest that sensory attenuation effects typically seen in fingertip force production play an important role in the control of speech volume.

Updates on Vocal Tremor and its Management

Vocal tremor is a neurogenic voice disorder characterized by a nearly periodic modulation in pitch and loudness during sustained phonation. This voicing pattern is the result of tremor affecting structures within the speech mechanism, resulting in modulation of lung pressure, phonation, articulation, and resonance during speaking. Speaking patterns in these individuals may be perceived as similar to spasmodic dysphonia or muscle tension dysphonia. The key to determining the presence of vocal tremor and distinguishing it from other voice disorders requires familiarity with the perceptual, acoustic, and physiologic patterns associated with vocal tremor during different voicing and speech contexts. Management of those with vocal tremor can be challenging because of its co-occurrence with other neurological disorders. The two most common methods for managing vocal tremor include pharmaceutical treatment, most commonly applied via injections of Botulinum Toxin Type A (Botox®), and behavioral modification of speaking patterns. The latter approach is in early clinical phases of research and has not yet been subjected to clinical trials. In this paper, I will summarize the clinical characteristics of vocal tremor in comparison to what is known about tremor in general and describe Botox® and behavioral approaches for managing individuals with this voice disorder.

Effects of masking noise on laryngeal resistance for breathy, normal, and pressed voice

PURPOSE

The purpose of the present study was to explore the effects of masking noise on laryngeal resistance for breathy, normal, and pressed voice in vocally trained women.

METHOD

Eighteen vocally trained women produced breathy, normal, and pressed voice across 7 fundamental frequencies during a repeated CV utterance of /pi/ under normal and masked auditory feedback. Dependent variables were mean and standard deviation of laryngeal resistance (LR; cmH2O/l/s).

RESULTS

LR values for breathy and normal voice remained constant across normal and masked auditory feedback, whereas LR values for pressed voice increased significantly from normal to masked auditory feedback.

CONCLUSIONS

The results suggest that both voice pattern and feedback condition influenced the stability of the LR data. Specifically, the pressed voice pattern may be more susceptible to auditory feedback influence because it was less stable than the breathy and the normal voice patterns. Future investigation should continue to explore the relevance of auditory feedback for theoretical and clinical issues surrounding voice.

Influence of sound immersion and communicative interaction on the Lombard effect

PURPOSE

To examine the influence of sound immersion techniques and speech production tasks on speech adaptation in noise.

METHOD

In Experiment 1, we compared the modification of speakers' perception and speech production in noise when noise is played into headphones (with and without additional self-monitoring feedback) or over loudspeakers. We also examined how this sound immersion effect depends on noise type (broadband or cocktail party) and level (from 62 to 86dB SPL). In Experiment 2, we compared the modification of acoustic and lip articulatory parameters in noise when speakers interact or not with a speech partner.

RESULTS

Speech modifications in noise were greater when cocktail party noise was played in headphones than over loudspeakers. Such an effect was less noticeable in broadband noise. Adding a self-monitoring feedback into headphones reduced this effect but did not completely compensate for it. Speech modifications in noise were greater in interactive situation and concerned parameters that may not be related to voice intensity.

CONCLUSIONS

The results support the idea that the Lombard effect is both a communicative adaptation and an automatic regulation of vocal intensity. The influence of auditory and communicative factors has some methodological implications on the choice of appropriate paradigms to study the Lombard effect.

Laryngeal-Level Amplitude Modulation in Vibrato

The goal of this investigation was to test a new methodology for measuring amplitude modulation (AM) at the level of the vocal folds during vibrato in trained singers, because previous research has suggested that AM arises in large part as an acoustic epiphenomenon through an interaction of the harmonics in the laryngeal source with the resonances of the vocal tract as the fundamental frequency oscillates. A within-subjects model was used to compare vocal activity across three pitch and three loudness conditions. Seventeen female singers with a range of training and experience were recorded with a microphone and an electroglottograph (EGG). Fluctuations in the ratio of closing to opening peaks in the first derivative of the EGG signal were used as an index of laryngeal-level AM. Evidence of laryngeal AM was found to a greater or lesser extent in all the singers, and its extent was not related to the degree of training. Across singers and pitch conditions, it was more prominent at lower intensities. The differentiated EGG signal lends itself to the measurement of AM at the level of the larynx, and the extent of the modulation appears more related to the level of vocal effort than to individual singer characteristics.

The relationship between pitch discrimination and vocal production: comparison of vocal and instrumental musicians

Auditory pitch discrimination and vocal pitch accuracy are fundamental abilities and essential skills of a professional singer; yet, the relationship between these abilities, particularly in trained vocal musicians, has not been the subject of much research. Difference limens for frequency (DLFs) and pitch production accuracy (PPA) were examined among 20 vocalists, 21 instrumentalists, and 21 nonmusicians. All were right-handed young adult females with normal hearing. Stimuli were harmonic tone complexes simulating piano tones and represented the mid-frequency of the untrained female vocal range, F0=261.63-392 Hz (C4-G4). DLFs were obtained by an adaptive psychophysical paradigm. Vocal pitch recordings were analyzed to determine PPA. Musicians demonstrated superior pitch discrimination and production accuracy compared to nonmusicians. These abilities did not distinguish instrumentalists and vocalists. DLF and PPA were significantly correlated with each other only for musicians with instrumental training; however, PPA was most consistent with minimal variance for vocalists. It would appear that a relationship between DLF and PPA develops with musical training, and these abilities can be differentially influenced by the type of specialty training.

Reflexive and volitional voice fundamental frequency responses to an anticipated feedback pitch error

The pitch-shift reflex is a corrective voice fundamental frequency (F0) response triggered by a sudden shift or "error" in auditory feedback pitch. We investigated how anticipating a voice pitch error affects the pitch-shift reflex and volitional voice F0 responses. Adults sustained the vowel/u/at a comfortable pitch and pressed a button to deliver a 100 cent, 100 ms auditory feedback pitch shift immediately or after a random delay. Pitch shift direction was either constant (up) or randomized (up or down). Onset anticipation often resulted in an anticipatory voice F0 change, but stimulus direction predictability did not affect the responses. When pitch error onset and direction were both anticipated, some participants produced an ideomotor voice F0 change that partially imitated the error, but they produced no apparent pitch-shift reflex. Results imply that when voice pitch errors are anticipated, volitional voice F0 responses may reduce or enhance voice F0 stability.

Estimating subglottal pressure via airflow interruption with auditory masking

Current noninvasive measurement of subglottal pressure using airflow interruption often produces inconsistent results due to the elicitation of audio-laryngeal reflexes. Auditory feedback could be considered as a means of ensuring measurement accuracy and precision. The purpose of this study was to determine if auditory masking could be used with the airflow interruption system to improve intrasubject consistency. A prerecorded sample of subject phonation was played on a loop over headphones during the trials with auditory masking. This provided subjects with a target pitch and blocked out distracting ambient noise created by the airflow interrupter. Subglottal pressure was noninvasively measured using the airflow interruption system. Thirty subjects, divided into two equal groups, performed 10 trials without auditory masking and 10 trials with auditory masking. Group one performed the normal trials first, followed by the trials with auditory masking. Group two performed the auditory masking trials first, followed by the normal trials. Intrasubject consistency was improved by adding auditory masking, resulting in a decrease in average intrasubject standard deviation from 0.93+/-0.51 to 0.47+/-0.22 cm H(2)O (P < 0.001). Auditory masking can be used effectively to combat audio-laryngeal reflexes and aid subjects in maintaining constant glottal configuration and frequency, thereby increasing intrasubject consistency when measuring subglottal pressure. By considering auditory feedback, a more reliable method of measurement was developed. This method could be used by clinicians, as reliable, immediately available values of subglottal pressure are useful in evaluating laryngeal health and monitoring treatment progress.

Effects of Speech Noise on Vocal Fundamental Frequency Using Power Spectral Analysis

OBJECTIVE

To investigate the relationship between auditory function and vocal fundamental frequency (F0) using binaural masking with speech noise during sustained vowel vocalization.

DESIGN

Eight healthy subjects were instructed to vocalize the sustained vowel /a/ at the intensities of 65 to 75 dBA and 90 to 100 dBA as steadily as possible. The phonations without noise masking were compared with the phonations under masking with 85-dBA speech noise presented to both ears through headphones. The F0s were obtained by using autocorrelation of the voice signals and were converted to cents to form a F0 sequence. The power spectrum of the F0 sequence was then acquired using fast Fourier transformation.

RESULTS

A significant increase in the power spectrum in the frequency range of <3 Hz (p < 0.05, paired Student t-test) appeared under noise masking. A negative feedback control of the auditory system on F0 is suggested regarding F0 modulations of <3 Hz.

CONCLUSIONS

The auditory system helps control a stable F0 during sustained vowel production by decreasing F0 modulation at <3 Hz. Power spectral analysis of F0 may be used to assess the interaction between F0 production and auditory feedback.

Compensation following real-time manipulation of formants in isolated vowels

Auditory feedback influences human speech production, as demonstrated by studies using rapid pitch and loudness changes. Feedback has also been investigated using the gradual manipulation of formants in adaptation studies with whispered speech. In the work reported here, the first formant of steady-state isolated vowels was unexpectedly altered within trials for voiced speech. This was achieved using a real-time formant tracking and filtering system developed for this purpose. The first formant of vowel /epsilon/ was manipulated 100% toward either /ae/ or /I/, and participants responded by altering their production with average Fl compensation as large as 16.3% and 10.6% of the applied formant shift, respectively. Compensation was estimated to begin <460 ms after stimulus onset. The rapid formant compensations found here suggest that auditory feedback control is similar for both F0 and formants.

Central nervous system control of the laryngeal muscles in humans

Laryngeal muscle control may vary for different functions such as: voice for speech communication, emotional expression during laughter and cry, breathing, swallowing, and cough. This review discusses the control of the human laryngeal muscles for some of these different functions. Sensori-motor aspects of laryngeal control have been studied by eliciting various laryngeal reflexes. The role of audition in learning and monitoring ongoing voice production for speech is well known; while the role of somatosensory feedback is less well understood. Reflexive control systems involving central pattern generators may contribute to swallowing, breathing and cough with greater cortical control during volitional tasks such as voice production for speech. Volitional control is much less well understood for each of these functions and likely involves the integration of cortical and subcortical circuits. The new frontier is the study of the central control of the laryngeal musculature for voice, swallowing and breathing and how volitional and reflexive control systems may interact in humans.