Effects of simultaneous perturbations of voice pitch and loudness feedback on voice F0 and amplitude control

The Accompanying Effect in Responses to Auditory Perturbations: Unconscious Vocal Adjustments to Unperturbed Parameters

PURPOSE

The present study examined whether participants respond to unperturbed parameters while experiencing specific perturbations in auditory feedback. For instance, we aim to determine if speakers adjust voice loudness when only pitch is artificially altered in auditory feedback. This phenomenon is referred to as the "accompanying effect" in the present study.

METHOD

Thirty native Mandarin speakers were asked to sustain the vowel /ɛ/ for 3 s while their auditory feedback underwent single shifts in one of the three distinct ways: pitch shift (±100 cents; coded as PT), loudness shift (±6 dB; coded as LD), or first formant (F1) shift (±100 Hz; coded as FM). Participants were instructed to ignore the perturbations in their auditory feedback. Response types were categorized based on pitch, loudness, and F1 for each individual trial, such as Popp_Lopp_Fopp indicating opposing responses in all three domains.

RESULTS

The accompanying effect appeared 93% of the time. Bayesian Poisson regression models indicate that opposing responses in all three domains (Popp_Lopp_Fopp) were the most prevalent response type across the conditions (PT, LD, and FM). The more frequently used response types exhibited opposing responses and significantly larger response curves than the less frequently used response types. Following responses became more prevalent only when the perturbed stimuli were perceived as voices from someone else (external references), particularly in the FM condition. In terms of isotropy, loudness and F1 tended to change in the same direction rather than loudness and pitch.

CONCLUSION

The presence of the accompanying effect suggests that the motor systems responsible for regulating pitch, loudness, and formants are not entirely independent but rather interconnected to some degree.

Controlling Pitch for Prosody: Sensorimotor Adaptation in Linguistically Meaningful Contexts

PURPOSE

This study examined how speakers adapt to fundamental frequency (fo) errors that affect the use of prosody to convey linguistic meaning, whether fo adaptation in that context relates to adaptation in linguistically neutral sustained vowels, and whether cue trading is reflected in responses in the prosodic cues of fo and amplitude.

METHOD

Twenty-four speakers said vowels and sentences while fo was digitally altered to induce predictable errors. Shifts in fo (±200 cents) were applied to the entire sustained vowel and one word (emphasized or unemphasized) in sentences. Two prosodic cues-fo and amplitude-were extracted. The effects of fo shifts, shift direction, and emphasis on fo response magnitude were evaluated with repeated-measures analyses of variance. Relationships between adaptive fo responses in sentences and vowels and between adaptive fo and amplitude responses were evaluated with Spearman correlations.

RESULTS

Speakers adapted to fo errors in both linguistically meaningful sentences and linguistically neutral vowels. Adaptive fo responses of unemphasized words were smaller than those of emphasized words when fo was shifted upward. There was no relationship between adaptive fo responses in vowels and emphasized words, but adaptive fo and amplitude responses were strongly, positively correlated.

CONCLUSIONS

Sensorimotor adaptation occurs in response to fo errors regardless of how disruptive the error is to linguistic meaning. Adaptation to fo errors during sustained vowels may not involve the exact same mechanisms as sensorimotor adaptation as it occurs in meaningful speech. The relationship between adaptive responses in fo and amplitude supports an integrated model of prosody.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.25008908.

Impairment of the internal forward model and feedback mechanisms for vocal sensorimotor control in post-stroke aphasia: evidence from directional responses to altered auditory feedback

The present study examined opposing and following vocal responses to altered auditory feedback (AAF) to determine how damage to left-hemisphere brain networks impairs the internal forward model and feedback mechanisms in post-stroke aphasia. Forty-nine subjects with aphasia and sixty age-matched controls performed speech vowel production tasks while their auditory feedback was altered using randomized ± 100 cents upward and downward pitch-shift stimuli. Data analysis revealed that when vocal responses were averaged across all trials (i.e., opposing and following), the overall magnitude of vocal compensation was significantly reduced in the aphasia group compared with controls. In addition, when vocal responses were analyzed separately for opposing and following trials, subjects in the aphasia group showed a significantly lower percentage of opposing and higher percentage of following vocal response trials compared with controls, particularly for the upward pitch-shift stimuli. However, there was no significant difference in the magnitude of opposing and following vocal responses between the two groups. These findings further support previous evidence on the impairment of vocal sensorimotor control in aphasia and provide new insights into the distinctive impact of left-hemisphere stroke on the internal forward model and feedback mechanisms. In this context, we propose that the lower percentage of opposing responses in aphasia may be accounted for by deficits in feedback-dependent mechanisms of audio-vocal integration and motor control. In addition, the higher percentage of following responses may reflect aberrantly increased reliance of the speech system on the internal forward model for generating sensory predictions during vocal error detection and motor control.

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.

Auditory-Motor Function Pre- and Post-Therapy in Hyperfunctional Voice Disorders: A Case Series

OBJECTIVE/HYPOTHESIS

Behavioral voice therapy is the most common treatment for hyperfunctional voice disorders (HVDs) but has limited long-term effectiveness since the comprehensive mechanisms underlying HVDs remain unclear. Recent work has implicated disordered sensorimotor integration during speech in some speakers with HVDs and suggests that auditory processing is a key factor to consider in HVD assessment and therapy. The purpose of this case-series study was to assess whether current voice therapy approaches for HVDs resulted in improvements to auditory-motor function.

STUDY DESIGN

Longitudinal (pre-post) study.

METHOD

Pre and postvoice therapy for HVDs, 11 speakers underwent an assessment of auditory-motor function via auditory discrimination of vocal pitch, responses to unanticipated auditory perturbations, and responses to predictable auditory perturbations of vocal pitch.

RESULTS

At the post-therapy session, 10 out of 11 participants demonstrated voice therapy success (via self-reported voice problems and/or auditory-perceptual judgements of voice by a clinician) and eight of the 11 participants demonstrated improvements in at least one measure of auditory discrimination and/or auditory-motor control. Specifically, three speakers demonstrated improvements in auditory discrimination, five speakers demonstrated improved (within typical cutoffs) responses to predictable perturbations, and two speakers demonstrated improvements in both auditory discrimination and auditory-motor measures.

CONCLUSIONS

Together, these findings support that voice therapy in individuals with HVDs may impact auditory-motor control and highlight the potential benefit of systematically addressing auditory function in voice therapy and assessment for HVDs.

The Effect of Pitch and Loudness Auditory Feedback Perturbations on Vocal Quality During Sustained Phonation

OBJECTIVE

Dysphonia is a reduction in vocal quality that impacts communication and is often an early sign of a voice disorder. There is little information regarding the effects of auditory feedback control of loudness and pitch on voice quality. In this study, we used both loudness-shift and pitch-shift paradigms to study the relationship between auditory feedback control and vocal quality as measured by smoothed cepstral peak prominence (CPPS), which reflects the harmonicity of the voice signal.

STUDY DESIGN

Experimental, mixed design.

METHODS

We applied 200 ms loudness-shifts (± 0, 3, or 6 dB) and pitch-shifts (± 0, 50, and 100 cents) to auditory feedback during sustained vowel production in 25 healthy adults. We then measured CPPS before and after the loudness-shift or pitch-shift to investigate the effect of changes in auditory feedback on vocal harmonicity.

RESULTS & CONCLUSIONS

Results showed that, on average, CPPS significantly decreased between the first half of the measured segment and the last half of the segment in the absence of auditory feedback shifts, suggesting that voice quality may be reduced across longer vowels over time. Upward and downward shifts in loudness auditory feedback caused a relative increase in CPPS, indicating an improvement in vocal harmonicity, even in cases when vocal intensity was reduced. Pitch alterations had inconsistent and minimal effects. We propose that there may be a control mechanism for voice quality that increases harmonicity of the voice signal to improve voice audibility (ie, ability to be heard) in the presence of unpredictable variability in voice intensity.

Identifying distinct latent classes of pitch-shift response consistency: Evidence from manipulating the predictability of shift direction

Auditory feedback plays an important role in regulating our vocal pitch. When pitch shifts suddenly appear in auditory feedback, the majority of the responses are opposing, correcting for the mismatch between perceived pitch and actual pitch. However, research has indicated that following responses to auditory perturbation could be common. This study attempts to explore the ways individual speakers would respond to pitch perturbation (using an opposing response or a following response) from trial to trial. Thirty-six native speakers of Mandarin produced the vowel /a/ while receiving perturbed pitch at a random time (500 ~ 700 ms) after vocal onset for a duration of 200 ms. Three blocks of 30 trials that differed in the pitch-shift stimulus direction were recorded in a randomized order: (a) the down-only condition where pitch was shifted downwards 250 cents; (b) the up-only condition where pitch was shifted upwards 250 cents; and (c) the random condition where downshifts and upshifts occurred randomly and were equally likely. The participants were instructed to ignore the pitch shifts. Results from the latent class analysis show that at the individual level across trials, 57% of participants were switchers, 28% were opposers, and 15% were followers. Our results support that speakers produce a mix of opposing and following responses when they respond to perturbed pitch. Specifically, the proportion of followers was conditional on the expectancy of pitch-shift stimulus direction: More followers were observed when the pitch-shift stimulus direction was predictable. Closer inspection of the levels of response consistency in different time phases shows that a particular mechanism (opposing or following) was initially implemented; the two mechanisms may alternate in the middle phase; and then finally, the pitch-shift response was featured as a particular mechanism near the end phase.

Task-Dependent Modulation of Auditory Feedback Control of Vocal Intensity

Auditory feedback control of fundamental frequency (fo) is modulated in a task-dependent manner. When voice pitch auditory feedback perturbations are applied in sentence versus sustained-vowel production, larger and faster vocal fo responses are measured in sentence production. This task-dependency reflects the scaling of auditory targets for pitch for the precision required in each speech task. When the range for the pitch auditory target is scaled down for precision (as in the sentence-production task), a greater degree of mismatch is detected from the feedback perturbation and a larger vocal response is measured. The purpose of this study was to determine whether auditory feedback control of vocal intensity is also modulated in a task-dependent manner similar to the control of vocal pitch. Twenty-five English speakers produced repetitions of a sentence and a sustained vowel while hearing their voice auditory feedback briefly perturbed in loudness (+/- 3 or 6 dB SPL, 200 ms duration). The resulting vocal intensity responses were measured, and response magnitudes were robustly larger in the sentence (mean: 1.96 dB) than vowel production (mean: 0.89 dB). Additionally, response magnitudes increased as a function of perturbation magnitude only in sentence production for downward perturbations but decreased in magnitude by perturbation magnitude for upward perturbations. Peak response latencies were robustly shorter in sentence (mean: 184.94 ms) than in vowel production (mean: 214.92 ms). Overall, these results support the hypothesis that auditory feedback control of pitch and loudness are modulated by task and that both pitch and loudness auditory targets are scaled for the precision required for the speaking task.

Comparison of Involuntary and Volitional Responses to Pitch-Shifted Auditory Feedback: Evidence for Tone Speakers' Flexibility to Switch Between Opposing and Following Responses

PURPOSE

Our audio-vocal system involves a negative feedback system that functions to correct for fundamental frequency (f ₀) errors in production. Therefore, automatic and opposing responses appear when an unexpected change in voice pitch is present in auditory feedback. This study explores following responses to pitch perturbation in auditory feedback in tonal language speakers, which have been commonly overlooked or discarded by past research. We examine whether the number of response types (opposing vs. following) and their dynamic f ₀ contours in tone word production vary as a function of instruction (involuntary ["to ignore"] vs. volitional ["to compensate"]).

METHOD

Twenty-four native speakers of Taiwanese Southern Min (TSM) produced three disyllabic TSM words while receiving pitch perturbation through headphones. The three disyllabic words were tsau⁵⁵-im⁵⁵ ("out of tune"; HH), kau³³-uann³³ ("exchange"; MM), and pan¹¹-an¹¹ ("handle a case"; LL) that carry an identical high-, mid-, or low-level tone. The participants were instructed either "to ignore" or "to compensate" for the pitch shifts.

RESULTS

Results from a Bayesian Poisson regression show that the number of opposing and following responses were split nearly 50-50 for the "ignore" condition and 55%-35% for the "compensate" condition. The simulation results indicate that the speakers were able to switch between the feedback and the feedforward mode during the testing. On the other hand, f ₀ contour analyses using generalized additive models show that pitch-increasing responses (i.e., oppose to downshifts or follow upshifts) were significantly larger than pitch-decreasing responses (i.e., oppose to upshifts or follow downshifts) for the MM and LL words, but not for the HH word.

CONCLUSIONS

Our results provide support for the view that, for tone speakers, following responses are not uncommon. The magnitudes of pitch shift response trajectories have to do with the available pitch range for moving up or down in tone word production.

Singing in different performance spaces: The effect of room acoustics on vibrato and pitch inaccuracy

Previous literature suggests that musical performers may be influenced to some extent by the acoustic environment in which they sing or play. This study investigates the influence of room acoustics on singers' voice production, by analyzing consecutive sung performances of classically trained students in five different performance spaces. The analyzed voice parameters were vibrato rate, extent, and pitch inaccuracy. Nine classically trained student-singers performed the same aria unaccompanied on a variable starting pitch that was consistent between spaces. Variance in vibrato rate and pitch inaccuracy was primarily explained by individual differences between singers. Conversely, the variance attributable to the rooms for the parameter of vibrato extent was larger compared to the variance attributable to the performers. Vibrato extent tended to increase with room clarity (C80) and was inversely associated with early decay time (EDT). Additionally, pitch inaccuracy showed a significant negative association with room support (ST_v). Singers seem to adjust their vocal production when performing in different acoustic environments. Likewise, the degree to which a singer can hear themself on stage may influence pitch accuracy.

What Can Altered Auditory Feedback Paradigms Tell Us About Vocal Motor Control in Individuals With Voice Disorders?

Purpose

The goal of this review article is to provide a summary of the progression of altered auditory feedback (AAF) as a method to understand the pathophysiology of voice disorders. This review article focuses on populations with voice disorders that have thus far been studied using AAF, including individuals with Parkinson's disease, cerebellar degeneration, hyperfunctional voice disorders, vocal fold paralysis, and laryngeal dystonia. Studies using AAF have found that individuals with Parkinson's disease, cerebellar degeneration, and laryngeal dystonia have hyperactive auditory feedback responses due to differing underlying causes. In persons with PD, the hyperactivity may be a compensatory mechanism for atypically weak feedforward motor control. In individuals with cerebellar degeneration and laryngeal dystonia, the reasons for hyperactivity remain unknown. Individuals with hyperfunctional voice disorders may have auditory-motor integration deficits, suggesting atypical updating of feedforward motor control.

Conclusions

These findings have the potential to provide critical insights to clinicians in selecting the most effective therapy techniques for individuals with voice disorders. Future collaboration between clinicians and researchers with the shared objective of improving AAF as an ecologically feasible and valid tool for clinical assessment may provide more personalized therapy targets for individuals with voice disorders.

Pediatric Responses to Fundamental and Formant Frequency Altered Auditory Feedback: A Scoping Review

Purpose

The ability to hear ourselves speak has been shown to play an important role in the development and maintenance of fluent and coherent speech. Despite this, little is known about the developing speech motor control system throughout childhood, in particular if and how vocal and articulatory control may differ throughout development. A scoping review was undertaken to identify and describe the full range of studies investigating responses to frequency altered auditory feedback in pediatric populations and their contributions to our understanding of the development of auditory feedback control and sensorimotor learning in childhood and adolescence.

Method

Relevant studies were identified through a comprehensive search strategy of six academic databases for studies that included (a) real-time perturbation of frequency in auditory input, (b) an analysis of immediate effects on speech, and (c) participants aged 18 years or younger.

Results

Twenty-three articles met inclusion criteria. Across studies, there was a wide variety of designs, outcomes and measures used. Manipulations included fundamental frequency (9 studies), formant frequency (12), frequency centroid of fricatives (1), and both fundamental and formant frequencies (1). Study designs included contrasts across childhood, between children and adults, and between typical, pediatric clinical and adult populations. Measures primarily explored acoustic properties of speech responses (latency, magnitude, and variability). Some studies additionally examined the association of these acoustic responses with clinical measures (e.g., stuttering severity and reading ability), and neural measures using electrophysiology and magnetic resonance imaging.

Conclusion

Findings indicated that children above 4 years generally compensated in the opposite direction of the manipulation, however, in several cases not as effectively as adults. Overall, results varied greatly due to the broad range of manipulations and designs used, making generalization challenging. Differences found between age groups in the features of the compensatory vocal responses, latency of responses, vocal variability and perceptual abilities, suggest that maturational changes may be occurring in the speech motor control system, affecting the extent to which auditory feedback is used to modify internal sensorimotor representations. Varied findings suggest vocal control develops prior to articulatory control. Future studies with multiple outcome measures, manipulations, and more expansive age ranges are needed to elucidate findings.

The effect of simulated insertion depth differences on the vocal pitches of cochlear implant users

Cochlear implant (CI) users often produce different vocal pitches when using their left versus right CI. One possible explanation for this is that insertion depth differs across the two CIs. The goal of this study was to investigate the role of electrode insertion depth in the production of vocal pitch. Eleven individuals with bilateral CIs used maps simulating differences in insertion depth. Participants produced a sustained vowel and sang Happy Birthday. Approximately half the participants significantly shifted the pitch of their voice in response to different simulated insertion depths. The results suggest insertion depth differences can alter produced vocal pitch.

Early Cochlear Implantation Allows Deaf Children to Control Voice Pitch and Loudness independently

OBJECTIVE

Congenitally deaf children with a cochlear implant (CI) improve their speech production intelligibility, but their prosody, including stress and intonation produced by voice pitch and loudness changes, often differs from normal hearing people, which affects their fluent oral communication. This study is aimed to clarify abnormal characteristics of voice pitch and loudness control in CI recipients using a newly developed visually guided pitch change task.

METHODS

We included 13 normal hearing volunteers (NH group) and 17 congenitally deaf CI users who showed good speech intelligibility. The 17 CI users were divided into Early-CI and Late-CI groups, based on their age at implantation of 2.5 years. Using the visually guided pitch change task and acoustic voice analysis of sustained vowels, we assessed their vocal skills to maintain constant pitch and loudness and intentionally change the voice pitch independent from loudness. At the time of examination, the mean age was 24.1, 12.7, and 18.9 years in the NH, Early-CI, and Late-CI groups.

RESULTS

During constant vowel production, Early-CI and Late-CI groups showed more significant fluctuations in pitch and loudness than the NH group. However, when focusing on intentionally changing only the pitch of the voice, the Early-CI group was significantly better than the Late-CI group and comparable to the NH group in terms of their ability to change vocal pitch independently from loudness.

CONCLUSION

Among congenitally deaf patients, age at implantation was associated with the development of voice skills to control voice pitch and loudness separately, which may influence their fluent prosody production.

Acoustic Features of Cry of Deaf and Hard-of-Hearing Infants

Previous research has demonstrated differences in the acoustic features of crying signals between deaf and typical hearing (TH) infants. This study aims at comparing the acoustic parameters of cries of infants with different degrees of deafness versus TH infants. About 110 infants aged 6-12 months (61 TH infants, 34 infants with bilateral deafness of variable degrees and 15 infants with unilateral deafness) were enrolled in the study. Results indicated that the most important acoustic parameters to demonstrate the difference between the crying of TH infants and deaf and hard-of-hearing (DHH) infants as well as between the crying of infants with different degrees of deafness are F0, cry duration, intensity, F2, and F4. In terms of accuracy, the parameter that showed the highest accuracy to differentiate between TH infants and DHH infants was F0 (74.5%). The accuracy of the combined acoustic parameters (F0, cry duration, intensity, and F4) was 70%. F0 was considered the best predictor and F4 the second best predictor of severity of deafness.

Speech Intensity Response to Altered Intensity Feedback in Individuals With Parkinson's Disease

Purpose Hypophonia (low speech intensity) is the most common speech symptom experienced by individuals with Parkinson's disease (IWPD). Previous research suggests that, in IWPD, there may be abnormal integration of sensory information for motor production of speech intensity. In the current study, intensity of auditory feedback was systematically manipulated (altered in both positive and negative directions) during sensorimotor conditions that are known to modulate speech intensity in everyday contexts in order to better understand the role of auditory feedback for speech intensity regulation. Method Twenty-six IWPD and 24 neurologically healthy controls were asked to complete the following tasks: converse with the experimenter, start vowel production, and read sentences at a comfortable loudness, while hearing their own speech intensity randomly altered. Altered intensity feedback conditions included 5-, 10-, and 15-dB reductions and increases in the feedback intensity. Speech tasks were completed in no noise and in background noise. Results IWPD displayed a reduced response to the altered intensity feedback compared to control participants. This reduced response was most apparent when participants were speaking in background noise. Specific task-based differences in responses were observed such that the reduced response by IWPD was most pronounced during the conversation task. Conclusions The current study suggests that IWPD have abnormal processing of auditory information for speech intensity regulation, and this disruption particularly impacts their ability to regulate speech intensity in the context of speech tasks with clear communicative goals (i.e., conversational speech) and speaking in background noise.

Speech compensation responses and sensorimotor adaptation to formant feedback perturbations

Control of speech formants is important for the production of distinguishable speech sounds and is achieved with both feedback and learned feedforward control. However, it is unclear whether the learning of feedforward control involves the mechanisms of feedback control. Speakers have been shown to compensate for unpredictable transient mid-utterance perturbations of pitch and loudness feedback, demonstrating online feedback control of these speech features. To determine whether similar feedback control mechanisms exist in the production of formants, responses to unpredictable vowel formant feedback perturbations were examined. Results showed similar within-trial compensatory responses to formant perturbations that were presented at utterance onset and mid-utterance. The relationship between online feedback compensation to unpredictable formant perturbations and sensorimotor adaptation to consistent formant perturbations was further examined. Within-trial online compensation responses were not correlated with across-trial sensorimotor adaptation. A detailed analysis of within-trial time course dynamics across trials during sensorimotor adaptation revealed that across-trial sensorimotor adaptation responses did not result from an incorporation of within-trial compensation response. These findings suggest that online feedback compensation and sensorimotor adaptation are governed by distinct neural mechanisms. These findings have important implications for models of speech motor control in terms of how feedback and feedforward control mechanisms are implemented.

Auditory-Motor Perturbations of Voice Fundamental Frequency: Feedback Delay and Amplification

Purpose Gradual and sudden perturbations of vocal fundamental frequency (f _o), also known as adaptive and reflexive f _o perturbations, are techniques to study the influence of auditory feedback on voice f _o control mechanisms. Previous vocal f _o perturbations have incorporated varied setup-specific feedback delays and amplifications. Here, we investigated the effects of feedback delays (10-100 ms) and amplifications on both adaptive and reflexive f _o perturbation paradigms, encapsulating the variability in equipment-specific delays (3-45 ms) and amplifications utilized in previous experiments. Method Responses to adaptive and reflexive f _o perturbations were recorded in 24 typical speakers for four delay conditions (10, 40, 70, and 100 ms) or three amplification conditions (-10, +5, and +10 dB relative to microphone) in a counterbalanced order. Repeated-measures analyses of variance were carried out on the magnitude of f _o responses to determine the effect of feedback condition. Results There was a statistically significant effect of the level of auditory feedback amplification on the response magnitude during adaptive f _o perturbations, driven by the difference between +10- and -10-dB amplification conditions (hold phase difference: M = 38.3 cents, SD = 51.2 cents; after-effect phase: M = 66.1 cents, SD = 84.6 cents). No other statistically significant effects of condition were found for either paradigm. Conclusions Experimental equipment delays below 100 ms in behavioral paradigms do not affect the results of f _o perturbation paradigms. As there is no statistically significant difference between the response magnitudes elicited by +5- and +10-dB auditory amplification conditions, this study is a confirmation that an auditory feedback amplification of +5 dB relative to microphone is sufficient to elicit robust compensatory responses for f _o perturbation paradigms.

Does passive sound attenuation affect responses to pitch-shifted auditory feedback?

The role of auditory feedback in vocal production has mainly been investigated by altered auditory feedback (AAF) in real time. In response, speakers compensate by shifting their speech output in the opposite direction. Current theory suggests this is caused by a mismatch between expected and observed feedback. A methodological issue is the difficulty to fully isolate the speaker's hearing so that only AAF is presented to their ears. As a result, participants may be presented with two simultaneous signals. If this is true, an alternative explanation is that responses to AAF depend on the contrast between the manipulated and the non-manipulated feedback. This hypothesis was tested by varying the passive sound attenuation (PSA). Participants vocalized while auditory feedback was unexpectedly pitch shifted. The feedback was played through three pairs of headphones with varying amounts of PSA. The participants' responses were not affected by the different levels of PSA. This suggests that across all three headphones, PSA is either good enough to make the manipulated feedback dominant, or differences in PSA are too small to affect the contribution of non-manipulated feedback. Overall, the results suggest that it is important to realize that non-manipulated auditory feedback could affect responses to AAF.

Mechanisms of voice control related to prosody in autism spectrum disorder and first-degree relatives

Differences in prosody (e.g., intonation, rhythm) are among the most obvious language-related impairments in autism spectrum disorder (ASD), and significantly impact communication. Subtle prosodic differences have also been identified in a subset of clinically unaffected first-degree relatives of individuals with ASD, and may reflect genetic liability to ASD. This study investigated the neural basis of prosodic differences in ASD and first-degree relatives through analysis of feedforward and feedback control involved in the planning, production, self-monitoring, and self-correction of speech by using a pitch-perturbed auditory feedback paradigm during sustained vowel and speech production. Results revealed larger vocal response magnitudes to pitch-perturbed auditory feedback across tasks in ASD and ASD parent groups, with differences in sustained vowel production driven by parents who displayed subclinical personality and language features associated with ASD (i.e., broad autism phenotype). Both ASD and ASD parent groups exhibited increased response onset latencies during sustained vowel production, while the ASD parent group exhibited decreased response onset latencies during speech production. Vocal response magnitudes across tasks were associated with prosodic atypicalities in both individuals with ASD and their parents. Exploratory event-related potential (ERP) analyses in a subgroup of participants during the sustained vowel task revealed reduced P1 ERP amplitudes in the ASD group, with similar trends observed in parents. Overall, results suggest underdeveloped feedforward systems and neural attenuation in detecting audio-vocal feedback may contribute to ASD-related prosodic atypicalities. Importantly, results implicate atypical audio-vocal integration as a marker of genetic risk to ASD, evident in ASD and among clinically unaffected relatives. Autism Res 2019, 12: 1192-1210. © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc. LAY SUMMARY: Previous research has identified atypicalities in prosody (e.g., intonation) in individuals with ASD and a subset of their first-degree relatives. In order to better understand the mechanisms underlying prosodic differences in ASD, this study examined how individuals with ASD and their parents responded to unexpected differences in what they heard themselves say to modify control of their voice (i.e., audio-vocal integration). Results suggest that disruptions to audio-vocal integration in individuals with ASD contribute to ASD-related prosodic atypicalities, and the more subtle differences observed in parents could reflect underlying genetic liability to ASD.

Pitch Shifting With the Commercially Available Eventide Eclipse: Intended and Unintended Changes to the Speech Signal

Purpose This study details the intended and unintended consequences of pitch shifting with the commercially available Eventide Eclipse. Method Ten vocally healthy participants ( M = 22.0 years; 6 cisgender females, 4 cisgender males) produced a sustained /ɑ/, creating an input signal. This input signal was processed in near real time by the Eventide Eclipse to create an output signal that was either not shifted (0 cents), shifted +100 cents, or shifted -100 cents. Shifts occurred either throughout the entire vocalization or for a 200-ms period after vocal onset. Results Input signals were compared to output signals to examine potential changes. Average pitch-shift magnitudes were within 1 cent of the intended pitch shift. Measured pitch-shift length for intended 200-ms shifts was between 5.9% and 21.7% less than expected, based on the portion of shift selected for measurement. The delay between input and output signals was an average of 11.1 ms. Trials shifted +100 cents had a longer delay than trials shifted -100 or 0 cents. The first 2 formants (F1, F2) shifted in the direction of the pitch shift, with F1 shifting 6.5% and F2 shifting 6.0%. Conclusions The Eventide Eclipse is an accurate pitch-shifting hardware that can be used to explore voice and vocal motor control. The pitch-shifting algorithm shifts all frequencies, resulting in a subsequent change in F1 and F2 during pitch-shifted trials. Researchers using this device should be mindful of stimuli selection to avoid confusion during data interpretation.

Opposing and following responses in sensorimotor speech control: Why responses go both ways

When talking, speakers continuously monitor and use the auditory feedback of their own voice to control and inform speech production processes. When speakers are provided with auditory feedback that is perturbed in real time, most of them compensate for this by opposing the feedback perturbation. But some responses follow the perturbation. In the present study, we investigated whether the state of the speech production system at perturbation onset may determine what type of response (opposing or following) is made. The results suggest that whether a perturbation-related response is opposing or following depends on ongoing fluctuations of the production system: The system initially responds by doing the opposite of what it was doing. This effect and the nontrivial proportion of following responses suggest that current production models are inadequate: They need to account for why responses to unexpected sensory feedback depend on the production system's state at the time of perturbation.

Partial compensation to delayed auditory feedback: An analysis of syllable duration

Altered feedback perturbation studies have shown that speakers only partially compensate for shifts in vocal pitch, intensity, or spectral content. The partial compensation generally plateaus around 30%-40% of the non-shifted, baseline production and is proposed to reflect the integrated effect of altered (auditory) and non-altered (somatosensory) sensory feedback. The authors hypothesized that the same pattern should hold for changes in syllable duration with delayed auditory feedback. To test this, the authors calculated average syllable duration from 21 young adults who read a standard passage as auditory feedback was delayed by 0, 10, 50, 100, 200, 300, and 600 ms. Given the complex nature of speech errors elicited under delayed auditory feedback, the authors compared durational effects across two broad error categories: prolongations and repetitions. Average syllable duration increased non-linearly and reached a peak near 40% of baseline durations. Separated by error type, prolongations, and distortions made up 89% of perceived errors. Only 9% of perceived errors were identified as repetitions. Unlike prolongations, however, the duration of repeated tokens ranged from 74% to 110% of the target syllable and compensated fully for the delay. These results are consistent with the notion that increasing syllable duration compensates partially for delays in auditory feedback. The compensation pattern resembles that of responses to other forms of altered auditory feedback, which suggests that this may be a general attribute of low-level, sensorimotor compensation. The higher frequency of prolongation occurrences further suggests that these may be the primary means of compensation for delayed auditory feedback. Repetitions, on the other hand, likely reflect compensatory mechanisms of higher-level motor planning or sequencing processes.

Cochlear Implant Users' Vocal Control CorrelatesAcross Tasks

Cochlear implants (CIs) provide access to auditory information that can affect vocal control. For example, previous research shows that, when producing a sustained vowel, CI users will alter the pitch of their voice when the feedback of their own voice is perceived to shift. Although these results can be informative as to how perception and production are linked for CI users, the artificial nature of the task raises questions as to the applicability of the results to real-world vocal productions. To examine how vocal control, when producing sustained vowels, relates to vocal control for more ecologically valid tasks, 10 CI users' vocal control was measured across two tasks: (1) sustained vowel production, and (2) singing. The results found that vocal control, as measured by the variability of the participants' fundamental frequency, was significantly correlated when producing sustained vowels and when singing, although variability was significantly greater when singing. This suggests that, despite the artificial nature of sustained vowel production, vocal control on such tasks is related to vocal control for more ecologically valid tasks. However, the results also suggest that vocal control may be overestimated with sustained vowel production tasks.

The relationship between acoustical and perceptual measures of vocal effort

Excessive vocal effort is a common clinical voice symptom, yet the acoustical manifestation of vocal effort and how that is perceived by speakers and listeners has not been fully elucidated. Here, 26 vocally healthy adults increased vocal effort during the production of the utterance /ifi/, followed by self-ratings of effort on a 100 mm visual analog scale. Twenty inexperienced listeners assessed the speakers' vocal effort using the visual sort-and-rate method. Previously proposed acoustical correlates of vocal effort were calculated, including: mean sound pressure level (SPL), mean fundamental frequency (f o), relative fundamental frequency (RFF) offset cycle 10 and onset cycle 1, harmonics-to-noise ratio (HNR), cepstral peak prominence and its standard deviation (SD), and low-to-high (L/H) spectral ratio and its SD. Two separate mixed-effects regression models yielded mean SPL, L/H ratio, and HNR as significant predictors of both speaker and listener ratings of vocal effort. RFF offset cycle 10 and mean f o were significant predictors of listener ratings only. Therefore, speakers and listeners attended to similar acoustical cues when making judgments of vocal effort, but listeners also used additional time-based information. Further work is needed to determine how vocal effort manifests in the speech signal in speakers with voice disorders.

The functional relations among motor-based prediction, sensory goals and feedback in learning non-native speech sounds: Evidence from adult Mandarin Chinese speakers with an auditory feedback masking paradigm

Previous studies in speech production and acquisition have mainly focused on how feedback vs. goals and feedback vs. prediction regulate learning and speech control. The present study investigated the less studied mechanism-prediction vs. goals in the context of adult Mandarin speakers' acquisition of non-native sounds, using an auditory feedback masking paradigm. Participants were asked to learn two types of non-native vowels: /ø/ and /ɵ/-the former being less similar than the latter to Mandarin vowels, either in feedback available or feedback masked conditions. The results show that there was no significant improvement in learning the two targets when auditory feedback was masked. This suggests that motor-based prediction could not directly compare with sensory goals for adult second language acquisition. Furthermore, auditory feedback can help achieve learning only if the competition between prediction and goals is minimal, i.e., when target sounds are distinct from existing sounds in one's native speech. The results suggest motor-based prediction and sensory goals may share a similar neural representational format, which could result in a competing relation in neural recourses in speech learning. The feedback can conditionally overcome such interference between prediction and goals. Hence, the present study further probed the functional relations among key components (prediction, goals and feedback) of sensorimotor integration in speech learning.

When singing with cochlear implants, are two ears worse than one for perilingually/postlingually deaf individuals?

Many individuals with bilateral cochlear implants hear different pitches when listening with their left versus their right cochlear implant. This conflicting information could potentially increase the difficulty of singing with cochlear implants. To determine if bilateral cochlear implants are detrimental for singing abilities, ten perilingually/postlingually deaf bilateral adult cochlear implant users were asked to sing "Happy Birthday" when using their left, right, both, or neither cochlear implant. The results indicated that bilateral cochlear implant users have more difficulty singing the appropriate pitch contour when using both cochlear implants as opposed to the better ear alone.

Measuring vocal motor skill with a virtual voice-controlled slingshot

Successful voice training (e.g., singing lessons) and vocal rehabilitation (e.g., therapy for a voice disorder) involve learning complex, vocal behaviors. However, there are no metrics describing how humans learn new vocal skills or predicting how long the improved behavior will persist post-therapy. To develop measures capable of describing and predicting vocal motor learning, a theory-based paradigm from limb motor control inspired the development of a virtual task where subjects throw projectiles at a target via modifications in vocal pitch and loudness. Ten subjects with healthy voices practiced this complex vocal task for five days. The many-to-one mapping between the execution variables pitch and loudness and resulting target error was evaluated using an analysis that quantified distributional properties of variability: Tolerance, noise, covariation costs (TNC costs). Lag-1 autocorrelation (AC1) and detrended-fluctuation-analysis scaling index (SCI) analyzed temporal aspects of variability. Vocal data replicated limb-based findings: TNC costs were positively correlated with error; AC1 and SCI were modulated in relation to the task's solution manifold. The data suggests that vocal and limb motor learning are similar in how the learner navigates the solution space. Future work calls for investigating the game's potential to improve voice disorder diagnosis and treatment.

Modulation of auditory-motor learning in response to formant perturbation as a function of delayed auditory feedback

The interaction of language production and perception has been substantiated by empirical studies where speakers compensate their speech articulation in response to the manipulated sound of their voice heard in real-time as auditory feedback. A recent study by Max and Maffett [(2015). Neurosci. Lett. 591, 25-29] reported an absence of compensation (i.e., auditory-motor learning) for frequency-shifted formants when auditory feedback was delayed by 100 ms. In the present study, the effect of auditory feedback delay was studied when only the first formant was manipulated while delaying auditory feedback systematically. In experiment 1, a small yet significant compensation was observed even with 100 ms of auditory delay unlike the past report. This result suggests that the tolerance of feedback delay depends on different types of auditory errors being processed. In experiment 2, it was revealed that the amount of formant compensation had an inverse linear relationship with the amount of auditory delay. One of the speculated mechanisms to account for these results is that as auditory delay increases, undelayed (and unperturbed) somatosensory feedback is given more preference for accuracy control of vowel formants.

Occlusion effect on compensatory formant production and voice amplitude in response to real-time perturbation

The importance of auditory feedback for controlling speech articulation has been substantiated by the use of the real-time auditory perturbation paradigm. With this paradigm, speakers receive their own manipulated voice signal in real-time while they produce a simple speech segment. In response, they spontaneously compensate for the manipulation. In the case of vowel formant control, various studies have reported behavioral and neural mechanisms of how auditory feedback is processed for compensatory behavior. However, due to technical limitations such as avoiding an electromagnetic artifact or metal transducers near a scanner, some studies require foam tip insert earphones. These earphones occlude the ear canal, and may cause more energy of the unmanipulated first formant to reach the cochlea through bone conduction and thus confound the effect of formant manipulation. Moreover, amplification of lower frequencies due to occluded ear canals may influence speakers' voice amplitude. The current study examined whether using circumaural headphones and insert earphones would elicit different compensatory speech production when speakers' first formant was manipulated in real-time. The results of the current study showed that different headphones did not elicit different compensatory formant production. Voice amplitude results were varied across different vowels examined; however, voice amplitude tended to decrease with the introduction of F1 perturbation.

Responses to Intensity-Shifted Auditory Feedback During Running Speech

PURPOSE

Responses to intensity perturbation during running speech were measured to understand whether prosodic features are controlled in an independent or integrated manner.

METHOD

Nineteen English-speaking healthy adults (age range = 21-41 years) produced 480 sentences in which emphatic stress was placed on either the 1st or 2nd word. One participant group received an upward intensity perturbation during stressed word production, and the other group received a downward intensity perturbation. Compensations for perturbation were evaluated by comparing differences in participants' stressed and unstressed peak fundamental frequency (F0), peak intensity, and word duration during perturbed versus baseline trials.

RESULTS

Significant increases in stressed-unstressed peak intensities were observed during the ramp and perturbation phases of the experiment in the downward group only. Compensations for F0 and duration did not reach significance for either group.

CONCLUSIONS

Consistent with previous work, speakers appear sensitive to auditory perturbations that affect a desired linguistic goal. In contrast to previous work on F0 perturbation that supported an integrated-channel model of prosodic control, the current work only found evidence for intensity-specific compensation. This discrepancy may suggest different F0 and intensity control mechanisms, threshold-dependent prosodic modulation, or a combined control scheme.

Training of Working Memory Impacts Neural Processing of Vocal Pitch Regulation

Working memory training can improve the performance of tasks that were not trained. Whether auditory-motor integration for voice control can benefit from working memory training, however, remains unclear. The present event-related potential (ERP) study examined the impact of working memory training on the auditory-motor processing of vocal pitch. Trained participants underwent adaptive working memory training using a digit span backwards paradigm, while control participants did not receive any training. Before and after training, both trained and control participants were exposed to frequency-altered auditory feedback while producing vocalizations. After training, trained participants exhibited significantly decreased N1 amplitudes and increased P2 amplitudes in response to pitch errors in voice auditory feedback. In addition, there was a significant positive correlation between the degree of improvement in working memory capacity and the post-pre difference in P2 amplitudes. Training-related changes in the vocal compensation, however, were not observed. There was no systematic change in either vocal or cortical responses for control participants. These findings provide evidence that working memory training impacts the cortical processing of feedback errors in vocal pitch regulation. This enhanced cortical processing may be the result of increased neural efficiency in the detection of pitch errors between the intended and actual feedback.

Functional connectivity associated with acoustic stability during vowel production: implications for vocal-motor control

Vowels provide the acoustic foundation of communication through speech and song, but little is known about how the brain orchestrates their production. Positron emission tomography was used to study regional cerebral blood flow (rCBF) during sustained production of the vowel /a/. Acoustic and blood flow data from 13, normal, right-handed, native speakers of American English were analyzed to identify CBF patterns that predicted the stability of the first and second formants of this vowel. Formants are bands of resonance frequencies that provide vowel identity and contribute to voice quality. The results indicated that formant stability was directly associated with blood flow increases and decreases in both left- and right-sided brain regions. Secondary brain regions (those associated with the regions predicting formant stability) were more likely to have an indirect negative relationship with first formant variability, but an indirect positive relationship with second formant variability. These results are not definitive maps of vowel production, but they do suggest that the level of motor control necessary to produce stable vowels is reflected in the complexity of an underlying neural system. These results also extend a systems approach to functional image analysis, previously applied to normal and ataxic speech rate that is solely based on identifying patterns of brain activity associated with specific performance measures. Understanding the complex relationships between multiple brain regions and the acoustic characteristics of vocal stability may provide insight into the pathophysiology of the dysarthrias, vocal disorders, and other speech changes in neurological and psychiatric disorders.

Multiple factors are involved in the dysarthria associated with Parkinson's disease: a review with implications for clinical practice and research

PURPOSE

Motor speech abnormalities are highly common and debilitating in individuals with idiopathic Parkinson's disease (IPD). These abnormalities, collectively termed hypokinetic dysarthria (HKD), have been traditionally attributed to hypokinesia and bradykinesia secondary to muscle rigidity and dopamine deficits. However, the role of rigidity and dopamine in the development of HKD is far from clear. The purpose of the present study was to offer an alternative view of the factors underlying HKD.

METHOD

The authors conducted an extensive, but not exhaustive, review of the literature to examine the evidence for the traditional view versus the alternative view.

RESULTS

The review suggests that HKD is a highly complex and variable phenomenon including multiple factors, such as scaling and maintaining movement amplitude and effort; preplanning and initiation of movements; internal cueing; sensory and temporal processing; automaticity; emotive vocalization; and attention to action (vocal vigilance). Although not part of the dysarthria, nonmotor factors, such as depression, aging, and cognitive-linguistic abnormalities, are likely to contribute to the overall speech symptomatology associated with IPD.

CONCLUSION

These findings have important implications for clinical practice and research.

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.

Understanding the mechanisms underlying voluntary responses to pitch-shifted auditory feedback

Previous research has shown that vocal errors can be simulated using a pitch perturbation technique. Two types of responses are observed when subjects are asked to ignore changes in pitch during a steady vowel production, a compensatory response countering the direction of the perceived change in pitch and a following response in the same direction as the pitch perturbation. The present study investigated the nature of these responses by asking subjects to volitionally change their voice fundamental frequency either in the opposite direction ("opposing" group) or the same direction ("following" group) as the pitch shifts (±100 cents, 1000 ms) presented during the speaker's production of an /a/ vowel. Results showed that voluntary responses that followed the stimulus directions had significantly shorter latencies (150 ms) than opposing responses (360 ms). In addition, prior to the slower voluntary opposing responses, there were short latency involuntary responses that followed the stimulus direction. These following responses may involve mechanisms of imitation or vocal shadowing of acoustical stimuli when subjects are predisposed to respond to a change in frequency of a sound. The slower opposing responses may represent a control strategy that requires monitoring and correcting for errors between the feedback signal and the intended vocal goal.

Unexpected intensity changes in the ear canal during a F(0)-shifted feedback experiment

Effects of frequency-shifted feedback are typically examined using Eventide Harmonizer Series processors to shift the fundamental frequency (F0) of auditory feedback during vocalizations, eliciting compensatory shifts in speaker F0. Recently, unexpected intensity changes were observed in speakers' ear canals, corresponding with F0 shifts. An investigation revealed that feedback time delays introduced by the processor resulted in phase shifts between feedback and unprocessed voice signals radiating into the ear canal via bone conduction, producing combination waves with gains as high as 6 dB. Shifts of this magnitude potentially alter the interpretation of previously published results and should be controlled in future studies.

A bilateral cortical network responds to pitch perturbations in speech feedback

Auditory feedback is used to monitor and correct for errors in speech production, and one of the clearest demonstrations of this is the pitch perturbation reflex. During ongoing phonation, speakers respond rapidly to shifts of the pitch of their auditory feedback, altering their pitch production to oppose the direction of the applied pitch shift. In this study, we examine the timing of activity within a network of brain regions thought to be involved in mediating this behavior. To isolate auditory feedback processing relevant for motor control of speech, we used magnetoencephalography (MEG) to compare neural responses to speech onset and to transient (400ms) pitch feedback perturbations during speaking with responses to identical acoustic stimuli during passive listening. We found overlapping, but distinct bilateral cortical networks involved in monitoring speech onset and feedback alterations in ongoing speech. Responses to speech onset during speaking were suppressed in bilateral auditory and left ventral supramarginal gyrus/posterior superior temporal sulcus (vSMG/pSTS). In contrast, during pitch perturbations, activity was enhanced in bilateral vSMG/pSTS, bilateral premotor cortex, right primary auditory cortex, and left higher order auditory cortex. We also found speaking-induced delays in responses to both unaltered and altered speech in bilateral primary and secondary auditory regions, left vSMG/pSTS and right premotor cortex. The network dynamics reveal the cortical processing involved in both detecting the speech error and updating the motor plan to create the new pitch output. These results implicate vSMG/pSTS as critical in both monitoring auditory feedback and initiating rapid compensation to feedback errors.

Neurophysiological evidence of differential mechanisms involved in producing opposing and following responses to altered auditory feedback

OBJECTIVE

When hearing perturbations in voice auditory feedback, people produce responses that mostly oppose the perturbation direction, whereas a few responses follow the direction of feedback perturbation. The causes of opposing and following responses, however, remain poorly understood. The present event-related potential (ERP) study sought to examine the neurophysiological processing of opposing and following responses to pitch feedback perturbations during self-monitoring of vocal production.

METHOD

Twelve Mandarin-native speakers participated in the experiment. Vocal and neurophysiological responses to pitch perturbations (± 50 and ± 200 cents) in voice auditory feedback were measured. Individual-trial responses were categorized according to the response direction and then separately averaged in groups of opposing and following responses. ERPs indexed by the P1-N1-P2 complex corresponding to two types of vocal responses were also obtained.

RESULTS

Opposing and following vocal responses did not differ in the magnitude, but there were greater proportions of opposing to following responses to 50 cents stimuli. The amplitude and latency of the P1 and N1 components showed none of significance across conditions, whereas there was a direction × magnitude effect on the P2 response. Following responses elicited greater P2 amplitudes than opposing responses only when pitch feedback was perturbed for downward 200 cents, and upward pitch perturbation elicited greater P2 amplitudes than those with downward direction only in the production of opposing responses.

CONCLUSION

These findings demonstrate that cortical processing of opposing responses is different from that of following responses, which can be modulated by the physical properties of feedback perturbation.

SIGNIFICANCE

Different neural mechanisms are involved in the production of opposing and following responses to feedback perturbations during self-monitoring of vocal production.

Experience-dependent modulation of feedback integration during singing: role of the right anterior insula

Somatosensation plays an important role in the motor control of vocal functions, yet its neural correlate and relation to vocal learning is not well understood. We used fMRI in 17 trained singers and 12 nonsingers to study the effects of vocal-fold anesthesia on the vocal-motor singing network as a function of singing expertise. Tasks required participants to sing musical target intervals under normal conditions and after anesthesia. At the behavioral level, anesthesia altered pitch accuracy in both groups, but singers were less affected than nonsingers, indicating an experience-dependent effect of the intervention. At the neural level, this difference was accompanied by distinct patterns of decreased activation in singers (cortical and subcortical sensory and motor areas) and nonsingers (subcortical motor areas only) respectively, suggesting that anesthesia affected the higher-level voluntary (explicit) motor and sensorimotor integration network more in experienced singers, and the lower-level (implicit) subcortical motor loops in nonsingers. The right anterior insular cortex (AIC) was identified as the principal area dissociating the effect of expertise as a function of anesthesia by three separate sources of evidence. First, it responded differently to anesthesia in singers (decreased activation) and nonsingers (increased activation). Second, functional connectivity between AIC and bilateral A1, M1, and S1 was reduced in singers but augmented in nonsingers. Third, increased BOLD activity in right AIC in singers was correlated with larger pitch deviation under anesthesia. We conclude that the right AIC and sensory-motor areas play a role in experience-dependent modulation of feedback integration for vocal motor control during singing.

Opposing and following vocal responses to pitch-shifted auditory feedback: evidence for different mechanisms of voice pitch control

The present study describes a technique for analysis of vocal responses to auditory feedback pitch perturbations in which individual trials are first sorted according to response direction and then separately averaged in groups of upward or downward responses. In experiment 1, the stimulus direction was predictable (all upward) but magnitude was randomized between +100, +200, or +500 cents (unpredictable). Results showed that pitch-shift stimuli (PSS) of +100 and +200 cents elicited significantly larger opposing (compensatory) responses than +500 cent stimuli, but no such effect was observed for "following" responses. In experiment 2, subjects were tested in three blocks of trials where for the first two, PSS magnitude and direction were predictable (block 1+100 and block 2-100 cents), and in block 3, the magnitude was predictable (±100 cents) but direction was randomized (upward or downward). Results showed there were slightly more opposing than following responses for predictable PSS direction, but randomized directions led to significantly more opposing than following responses. Results suggest that predictability of stimulus direction and magnitude can modulate vocal responses to feedback pitch perturbations. The function and causes of the opposing and following responses are unknown, but there may be two different neural mechanisms involved in their production.

Neuronal mechanisms of voice control are affected by implicit expectancy of externally triggered perturbations in auditory feedback

Accurate vocal production relies on several factors including sensory feedback and the ability to predict future challenges to the control processes. Repetitive patterns of perturbations in sensory feedback by themselves elicit implicit expectations in the vocal control system regarding the timing, quality and direction of perturbations. In the present study, the predictability of voice pitch-shifted auditory feedback was experimentally manipulated. A block of trials where all pitch-shift stimuli were upward, and therefore predictable was contrasted against an unpredictable block of trials in which the stimulus direction was randomized between upward and downward pitch-shifts. It was found that predictable perturbations in voice auditory feedback led to a reduction in the proportion of compensatory vocal responses, which might be indicative of a reduction in vocal control. The predictable perturbations also led to a reduction in the magnitude of the N1 component of cortical Event Related Potentials (ERP) that was associated with the reflexive compensations to the perturbations. We hypothesize that formation of expectancy in our study is accompanied by involuntary allocation of attentional resources occurring as a result of habituation or learning, that in turn trigger limited and controlled exploration-related motor variability in the vocal control system.

ERP correlates of language-specific processing of auditory pitch feedback during self-vocalization

The present study investigated whether the neural correlates for auditory feedback control of vocal pitch can be shaped by tone language experience. Event-related potentials (P2/N1) were recorded from adult native speakers of Mandarin and Cantonese who heard their voice auditory feedback shifted in pitch by -50, -100, -200, or -500 cents when they sustained the vowel sound /u/. Cantonese speakers produced larger P2 amplitudes to -200 or -500 cents stimuli than Mandarin speakers, but this language effect failed to reach significance in the case of -50 or -100 cents. Moreover, Mandarin speakers produced shorter N1 latencies over the left hemisphere than the right hemisphere, whereas Cantonese speakers did not. These findings demonstrate that neural processing of auditory pitch feedback in vocal motor control is subject to language-dependent neural plasticity, suggesting that cortical mechanisms of auditory-vocal integration can be shaped by tone language experience.