Master of Science (MSc)
Faculty of Science
Jeffrey A. Jones
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.
Haweo, Colin S., "Neural and Behavioral Responses to the Use of Auditory Feedback in Vocal Control" (2009). Theses and Dissertations (Comprehensive). 913.