The proposed research seeks to address three basic questions about the role of auditory feedback in speech production. First: Does auditory feedback appear to be used as direct compensatory feedback in a negative feedback control system? The answer to this question will distinguish between two main types of speech production models, i.e., a) models in which auditory feedback can act directly on the immediate control of speech, and b) models in which auditory feedback has a more indirect role in controlling speech. These two types of models make differing predictions about a speaker's response to auditory feedback. The first predicts immediate compensation; the second predicts disruption followed by adaptation. A speech sensorimotor adaptation experiment, based on the paradigm developed in my thesis research, should resolve this issue by examining subjects' immediate responses to altered auditory feedback.

Second: Why does auditory feedback appear to be inhibited by the speech production system? It is hypothesized that the need for inhibition arises because of the delays inherent in the brain's transduction and processing of auditory feedback. A set of MEG experiments are proposed to address this issue. An initial experiment will document more carefully the existence of auditory feedback inhibition as indexed by the amplitude of the M100 response in auditory cortex to self-produced speech, as compared with the responses to a recording of the same speech. The second experiment will consider the hypothesized cause of this inhibition by using the MEG paradigm of the first study to examine the effects of exposure to various manipulations of auditory feedback (including delayed auditory feedback) on the inhibition of auditory feedback.

Third: How does auditory feedback appear to be inhibited? Two hypotheses about this issue are proposed for evaluation: a) auditory feedback is inhibited by a fixed amount; b) auditory feedback is inhibited dynamically, with the level of inhibition a function of the speed of production of the speech movement. The two hypotheses make different predictions about the amount of auditory feedback inhibition that would be observed in the production of fast- versus slow-changing speech movements. An MEG experiment is proposed to distinguish between the two hypotheses, comparing the amount of auditory feedback inhibition (as indexed by M100 amplitude) in the production of fast- and slow- changing speech movements.

Understanding how auditory feedback is used in speech production has been an important research topic for many decades because of its relevance to modeling the control of speech. It also has potential clinical applications to the treatment of speech production disorders such as stuttering and other dysphonias.