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

LaDIVA: A neurocomputational model providing laryngeal motor control for speech acquisition and production

Many voice disorders are the result of intricate neural and/or biomechanical impairments that are poorly understood. The limited knowledge of their etiological and pathophysiological mechanisms hampers effective clinical management. Behavioral studies have been used concurrently with computational models to better understand typical and pathological laryngeal motor control. Thus far, however, a unified computational framework that quantitatively integrates physiologically relevant models of phonation with the neural control of speech has not been developed. Here, we introduce LaDIVA, a novel neurocomputational model with physiologically based laryngeal motor control. We combined the DIVA model (an established neural network model of speech motor control) with the extended body-cover model (a physics-based vocal fold model). The resulting integrated model, LaDIVA, was validated by comparing its model simulations with behavioral responses to perturbations of auditory vocal fundamental frequency (fo) feedback in adults with typical speech. LaDIVA demonstrated capability to simulate different modes of laryngeal motor control, ranging from short-term (i.e., reflexive) and long-term (i.e., adaptive) auditory feedback paradigms, to generating prosodic contours in speech. Simulations showed that LaDIVA’s laryngeal motor control displays properties of motor equivalence, i.e., LaDIVA could robustly generate compensatory responses to reflexive vocal fo perturbations with varying initial laryngeal muscle activation levels leading to the same output. The model can also generate prosodic contours for studying laryngeal motor control in running speech. LaDIVA can expand the understanding of the physiology of human phonation to enable, for the first time, the investigation of causal effects of neural motor control in the fine structure of the vocal signal.

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.

Comparison of volitional opposing and following responses across speakers with different vocal histories

Research has shown that people who are instructed to volitionally respond to pitch-shifted feedback either produce responses that follow the shift direction with a short latency of 100-200 ms or oppose the shift direction with longer latencies of 300-400 ms. This difference in response latencies prompted a comparison of three groups of vocalists with differing abilities, non-trained English-speaking subjects, non-trained Mandarin-speaking subjects, and trained English-speaking singers. All subjects produced short latency following responses and long latency opposing responses, and in most cases the opposing responses were preceded by a shorter latency following response. Across groups, the magnitudes of the opposing and following responses were largest for the Mandarin speakers. Singers produced the smallest opposing response magnitudes, suggesting differences in the pitch goals of the two groups. Opposing response latencies were longest for the English and Mandarin speaking subjects and shortest for the trained singers, demonstrating that musical training increases the speed of producing the opposing responses. The presence of similar latencies of small following responses preceding larger opposing responses in all groups suggests that the tendency to mimic changes in sounds to which a person is attending are not influenced by vocal training or experience.

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.

Abnormal Speech Motor Control in Individuals with 16p11.2 Deletions

Speech and motor deficits are highly prevalent (>70%) in individuals with the 600 kb BP4-BP5 16p11.2 deletion; however, the mechanisms that drive these deficits are unclear, limiting our ability to target interventions and advance treatment. This study examined fundamental aspects of speech motor control in participants with the 16p11.2 deletion. To assess capacity for control of voice, we examined how accurately and quickly subjects changed the pitch of their voice within a trial to correct for a transient perturbation of the pitch of their auditory feedback. When compared to controls, 16p11.2 deletion carriers show an over-exaggerated pitch compensation response to unpredictable mid-vocalization pitch perturbations. We also examined sensorimotor adaptation of speech by assessing how subjects learned to adapt their sustained productions of formants (speech spectral peak frequencies important for vowel identity), in response to consistent changes in their auditory feedback during vowel production. Deletion carriers show reduced sensorimotor adaptation to sustained vowel identity changes in auditory feedback. These results together suggest that 16p11.2 deletion carriers have fundamental impairments in the basic mechanisms of speech motor control and these impairments may partially explain the deficits in speech and language in these individuals.

A temporal predictive code for voice motor control: Evidence from ERP and behavioral responses to pitch-shifted auditory feedback

The predictive coding model suggests that voice motor control is regulated by a process in which the mismatch (error) between feedforward predictions and sensory feedback is detected and used to correct vocal motor behavior. In this study, we investigated how predictions about timing of pitch perturbations in voice auditory feedback would modulate ERP and behavioral responses during vocal production. We designed six counterbalanced blocks in which a +100 cents pitch-shift stimulus perturbed voice auditory feedback during vowel sound vocalizations. In three blocks, there was a fixed delay (500, 750 or 1000 ms) between voice and pitch-shift stimulus onset (predictable), whereas in the other three blocks, stimulus onset delay was randomized between 500, 750 and 1000 ms (unpredictable). We found that subjects produced compensatory (opposing) vocal responses that started at 80 ms after the onset of the unpredictable stimuli. However, for predictable stimuli, subjects initiated vocal responses at 20 ms before and followed the direction of pitch shifts in voice feedback. Analysis of ERPs showed that the amplitudes of the N1 and P2 components were significantly reduced in response to predictable compared with unpredictable stimuli. These findings indicate that predictions about temporal features of sensory feedback can modulate vocal motor behavior. In the context of the predictive coding model, temporally-predictable stimuli are learned and reinforced by the internal feedforward system, and as indexed by the ERP suppression, the sensory feedback contribution is reduced for their processing. These findings provide new insights into the neural mechanisms of vocal production and motor control.

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.

Auditory-motor adaptation to frequency-altered auditory feedback occurs when participants ignore feedback

Background

Auditory feedback is important for accurate control of voice fundamental frequency (F₀). The purpose of this study was to address whether task instructions could influence the compensatory responding and sensorimotor adaptation that has been previously found when participants are presented with a series of frequency-altered feedback (FAF) trials. Trained singers and musically untrained participants (nonsingers) were informed that their auditory feedback would be manipulated in pitch while they sang the target vowel [/ɑ /]. Participants were instructed to either ‘compensate’ for, or ‘ignore’ the changes in auditory feedback. Whole utterance auditory feedback manipulations were either gradually presented (‘ramp’) in -2 cent increments down to -100 cents (1 semitone) or were suddenly (’constant‘) shifted down by 1 semitone.

Results

Results indicated that singers and nonsingers could not suppress their compensatory responses to FAF, nor could they reduce the sensorimotor adaptation observed during both the ramp and constant FAF trials.

Conclusions

Compared to previous research, these data suggest that musical training is effective in suppressing compensatory responses only when FAF occurs after vocal onset (500-2500 ms). Moreover, our data suggest that compensation and adaptation are automatic and are influenced little by conscious control.

Effect of tonal native language on voice fundamental frequency responses to pitch feedback perturbations during sustained vocalizations

The purpose of this cross-language study was to examine whether the online control of voice fundamental frequency (F(0)) during vowel phonation is influenced by language experience. Native speakers of Cantonese and Mandarin, both tonal languages spoken in China, participated in the experiments. Subjects were asked to vocalize a vowel sound /u/at their comfortable habitual F(0), during which their voice pitch was unexpectedly shifted (± 50, ± 100, ± 200, or ± 500 cents, 200 ms duration) and fed back instantaneously to them over headphones. The results showed that Cantonese speakers produced significantly smaller responses than Mandarin speakers when the stimulus magnitude varied from 200 to 500 cents. Further, response magnitudes decreased along with the increase in stimulus magnitude in Cantonese speakers, which was not observed in Mandarin speakers. These findings suggest that online control of voice F(0) during vocalization is sensitive to language experience. Further, systematic modulations of vocal responses across stimulus magnitude were observed in Cantonese speakers but not in Mandarin speakers, which indicates that this highly automatic feedback mechanism is sensitive to the specific tonal system of each language.

Effect of tonal native language on voice fundamental frequency responses to pitch feedback perturbations during sustained vocalizations

The purpose of this cross-language study was to examine whether the online control of voice fundamental frequency (F(0)) during vowel phonation is influenced by language experience. Native speakers of Cantonese and Mandarin, both tonal languages spoken in China, participated in the experiments. Subjects were asked to vocalize a vowel sound /u/at their comfortable habitual F(0), during which their voice pitch was unexpectedly shifted (± 50, ± 100, ± 200, or ± 500 cents, 200 ms duration) and fed back instantaneously to them over headphones. The results showed that Cantonese speakers produced significantly smaller responses than Mandarin speakers when the stimulus magnitude varied from 200 to 500 cents. Further, response magnitudes decreased along with the increase in stimulus magnitude in Cantonese speakers, which was not observed in Mandarin speakers. These findings suggest that online control of voice F(0) during vocalization is sensitive to language experience. Further, systematic modulations of vocal responses across stimulus magnitude were observed in Cantonese speakers but not in Mandarin speakers, which indicates that this highly automatic feedback mechanism is sensitive to the specific tonal system of each language.