The roles of auditory and somatosensory feedback in vocal motor control
Smith, Dante Joseph
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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.
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