Mechanisms of Online Control of Speech
Speech is central to human communication. One of the features of speech we control to make distinguishable speech is formants, which are the spectral frequencies in our speech that we vary to make different vowel sounds. It is well-understood that the control of speech features, including formants, depends heavily on feedback information. However, the exact mechanisms of feedback control of formants are not fully understood. The body of this dissertation investigates the feedback control of formants in different scenarios to explore its relationship with other speech control mechanisms. We first investigated the relationship of feedback control and the adaptation of feedforward control of formants and found that they have distinct mechanisms. We then explored the neural substrate of feedback processing for formants as compared to pitch using MEG, which allowed us to investigate network activity changes with a high temporal resolution. We found similar neural regions involved in feedback processing for both pitch and formants, though we observed opposite lateralization for pitch and formants across different frequency bands. Finally, we explored the interaction between auditory and somatosensory feedback information in the control of formants by attenuating oral somatosensory feedback using lidocaine while perturbing auditory feedback. We found a direction-dependent interaction between the two feedback modalities, specifically where we observed an increase in compensation responses to downward auditory feedback perturbations but a decrease in compensation responses to upward auditory feedback perturbations when the oral somatosensory feedback was attenuated.