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

A Robotic Voice Simulator and the Interactive Training for Hearing-Impaired People

A talking and singing robot which adaptively learns the vocalization skill by means of an auditory feedback learning algorithm is being developed. The robot consists of motor-controlled vocal organs such as vocal cords, a vocal tract and a nasal cavity to generate a natural voice imitating a human vocalization. In this study, the robot is applied to the training system of speech articulation for the hearing-impaired, because the robot is able to reproduce their vocalization and to teach them how it is to be improved to generate clear speech. The paper briefly introduces the mechanical construction of the robot and how it autonomously acquires the vocalization skill in the auditory feedback learning by listening to human speech. Then the training system is described, together with the evaluation of the speech training by auditory impaired people

The roles of auditory and somatosensory feedback in vocal motor control

Perturbing sensory feedback during speech is an often-used approach to characterizing feedback control mechanisms in speech and voice production. Auditory and somatosensory feedback are both engaged to correct perceived voice errors, but to date the role of somatosensory feedback control in voice remains unclear. Previous studies of somatosensory contributions to vocal control have involved mechanically displacing the larynx while observing compensatory responses in fundamental frequency (fo). These responses likely reflect a combination of auditory and somatosensory control processes, as sensory information was available in both domains. To isolate the individual contribution of each feedback controller, a laryngeal perturbation experiment was conducted with and without auditory feedback masking. Responses to the laryngeal perturbation experiment were compared to responses in an auditory perturbation experiment and in relation to a measure of auditory acuity. In the laryngeal perturbation experiment with auditory masking, the results indicated that participants compensated for the perturbation, suggesting that even when auditory feedback is unavailable, somatosensory feedback plays a role in correcting for errors. When auditory masking was removed, the level of compensation increased, supporting the idea that both sensory modalities are involved in correcting for errors when available. In the auditory perturbation experiment, participants compensated for the perturbation (a 100-cent downward shift in fo), but the amount of compensation was less than in the laryngeal perturbation experiment. This reduced compensation may be explained by the auditory and somatosensory feedback controllers working against each other. No relationship was found between participants’ compensations to the laryngeal and auditory perturbations, suggesting a lack of sensory preference across participants. Further, no relationships were found between auditory acuity and the level of compensation to the auditory perturbation, or auditory acuity and the contribution of auditory feedback to compensations in the laryngeal perturbation experiment. While models of speech motor control suggest that those with better sensory acuity should show greater compensation, our findings do not support this theory. This dissertation helps to elucidate the roles of auditory and somatosensory feedback in vocal motor control and lays the groundwork for future studies of vocal motor control mechanisms in populations with voice disorders

The Neurobiology of Human Vocalization: A Quantitative Meta-Analytic Approach

Vocalization is critical to communication and understanding the neural mechanisms that control voice is a critical scientific and clinical endeavor. Studies have used a variety of neuroimaging techniques to investigate the neural correlates of vocal control using perturbation tasks. These studies have provided substantial evidence that there is a critical role of the Superior Temporal Gyrus (STG) in error detection/correction during vocalization. The STG appears to function as a regulatory region within a complex network of brain areas that control human vocalization. The aims of this study were to 1) Use Activation Likelihood Estimation (ALE) analyses to substantiate the neural regions activation during vocalization; 2) To determine the functional significance of the neural regions activated during vocalization, as characterized by the BrainMap database; 3) To parcellate the bilateral STG by means of Connectivity Based Parcellation (CBP) and functionally characterize any discreate subregions found. Results of the vocalization ALE analysis revealed activation of the bilateral STG, right supplementary motor area, bilateral precentral gyrus, right inferior frontal gyrus, right pallidum, left putamen and right cerebellum (VI), which largely substantiates previous findings of the vocalization network. Results of CBP revealed six distinct subregions of the left and right STG, with major functional characterization in the domains of perception, action, and cognition and in the specific tasks of music production and stimulus monitoring/discrimination

Neural and Behavioral Responses to the Use of Auditory Feedback in Vocal Control

A large body of evidence suggests that the motor system maintains a forward model that predicts the sensory outcome of movements. When sensory feedback does not match the predicted consequences, a compensatory response corrects for the motor error and the forward model is updated to prevent future errors. Like other motor behaviours, vocalization relies on sensory feedback for the maintenance of forward models and to stabilize vocalizations. Experiment 1 used event-related potentials (ERPs) to examine sensory processing of short feedback perturbations during an ongoing utterance. In one session, participants produced a vowel at an FO of their own choosing. In another session, participants matched the FO of a cue voice. An FO perturbation of 0,25, 50,100, or 200 cents was introduced for 100 ms. A mismatch negativity (MMN) was observed. Differences between sessions were only found for 200 cents perturbations. Reduced compensation when speakers experienced the 200 cents perturbations suggests that this larger perturbation was perceived as externally generated. The presence of an MMN, and no earlier (N100) response suggests that the underlying sensory process used to identify and compensate for errors in mid-utterance may differ from feedback monitoring at utterance onset. In Experiment 2, we used a frequency altered feedback (FAF) paradigm to study the role of auditory feedback in the control of vocal pitch (F0). We adapted participants to a one semitone shift and induced a perturbation by briefly removing the altered feedback. This was compared to a control block in which a 1 semitone perturbation was introduced into an unshifted trial, or trials were randomly shifted up 1 semitone, and a perturbation was introduced by removing the feedback alteration. The compensation response to mid-utterance perturbations was identical in all conditions, and was always smaller than the compensation to a shift at utterance onset. These results are explained by a change in the control strategy at utterance onset and midutterance. At utterance onset, auditory feedback is compared to feedback predicted by a forward model to ensure the pitch goal is achieved. However, after utterance onset, the control strategy switches and stabilization is maintained by comparing feedback to previous FO production. Experiment 1 showed a MMN in response to a mid-utterance perturbation, which is distinct from the N100 found in previous studies that examined perturbations at utterance onset. This result suggests that there may be different underlying neurological mechanisms for the detection of perturbations at utterance onset and mid-utterance. Experiment 2 adds support for this idea by showing a difference in the compensation responses to mid-utterance and onset perturbations. We conclude that different mechanisms may be used to detect errors and compensate for these errors at utterance onset versus mid-utterance

Origins of vocal-entangled gesture

Gestures during speaking are typically understood in a representational framework: they represent absent or distal states of affairs by means of pointing, resemblance, or symbolic replacement. However, humans also gesture along with the rhythm of speaking, which is amenable to a non-representational perspective. Such a perspective centers on the phenomenon of vocal-entangled gestures and builds on evidence showing that when an upper limb with a certain mass decelerates/accelerates sufficiently, it yields impulses on the body that cascade in various ways into the respiratory–vocal system. It entails a physical entanglement between body motions, respiration, and vocal activities. It is shown that vocal-entangled gestures are realized in infant vocal–motor babbling before any representational use of gesture develops. Similarly, an overview is given of vocal-entangled processes in non-human animals. They can frequently be found in rats, bats, birds, and a range of other species that developed even earlier in the phylogenetic tree. Thus, the origins of human gesture lie in biomechanics, emerging early in ontogeny and running deep in phylogeny

An Examination of the Factors that Dictate the Relative Weighting of Feedback and Feedforward Input for Speech Motor Control

Speech is arguably the most important form of human communication. Fluent speech production relies on auditory feedback for the planning, execution, and monitoring of speech movements. Auditory feedback is particularly important during the acquisition of speech, however, it has been suggested that over time speakers rely less on auditory feedback as they develop robust sensorimotor representations that allow speech motor commands to be executed in a feedforward manner. The studies reported in this thesis recorded speaker’s vocal and neural responses to altered auditory feedback in order to explore the factors that dictate the relative importance of auditory feedback for speech motor control. More specifically, studies 1 through 3 examined how the role of auditory feedback changes throughout development, while studies 4 and 5 examined the relationship between vocal variability and auditory feedback control, and lastly study 6 looked at how the predictability of auditory feedback errors influences the role of auditory feedback for speech motor control. Results of the first study demonstrated that toddlers use auditory feedback to regulate their speech motor commands, supporting the long held notion that auditory feedback is important during the acquisition of speech. While mapping out the developmental trajectory of vocal and event related potential responses to altered auditory feedback, the second study demonstrated that vocal variability, rather than age, best predicts responses to altered auditory feedback. Importantly, this suggests that the maturation of the speech motor control system is not strictly dependent on age. The third study in this thesis demonstrated that children and adults show similar rates of sensorimotor adaptation, suggesting that once speech is acquired, speakers are proficient at using sensory information to modify the planning of future speech motor commands. However, since adults produced larger compensatory responses, these results also suggested that adults are more proficient at comparing incoming auditory feedback with the feedback predicted by their sensorimotor representations, as a result of possessing more precisely mapped sensorimotor representations. The results of studies four and five demonstrated that vocal variability can be used to predict the size of compensatory responses and sensorimotor adaptation to changes in one’s auditory feedback, respectively. Furthermore, these studies demonstrated that increased variability was related to increased auditory feedback control of speech. Finally, the sixth study in this thesis demonstrated that experimentally induced predictability and variability can be used to induce increases in feedforward and auditory feedback control, respectively. In conclusion, the results reported in this thesis demonstrate that age and vocal variability, both naturally occurring and experimentally induced, are important determinants of the role of auditory feedback in speech motor control