The role of auditory feedback during speech production

Access to auditory feedback regarding one's own speech seems particularly important for developing normal speech. When hearing is diminished or eliminated early in life, the quality of an individual's speech can be severely compromised or, at worst, speech will not develop. Auditory feedback appears to be necessary in order to develop internal representations that are used in speech motor control. Feedback remains necessary even after these internal representations have been formed. Postlingually acquired deafness often leads to a deterioration of many aspects of speech production. In addition, various laboratory studies have shown that altering auditory feedback affects speech production.;This evidence suggests that the nervous system organizes speech using "internal models" or representations of the forces and kinematics of vocal tract movements and the feedback regarding the acoustic consequences of those movements. This thesis explores the role of auditory feedback in learning novel relationships between vocal tract movements and their resulting speech sounds.;Subjects were exposed to modified auditory feedback regarding their vocal pitch. Short-term exposure to the altered feedback conditions led to aftereffects in pitch production when feedback was returned to normal. The adaptation suggests that a remapping between produced pitch and expected feedback occurred. In subsequent studies, speakers of Mandarin were asked to say words while receiving false feedback regarding their voice fundamental frequency. Mandarin is a tone language, which means that pitch has phonemic function. After a short period of exposure to frequency altered feedback, Mandarin speakers produced tones outside of their normal pitch range. Exposure to altered feedback while producing one tone also affected productions of another tone. The results suggest that despite the existence of an obligatory underlying phonemic representation, the acoustic-motor representation is malleable.;A final experiment investigated the role auditory feedback plays when the physical characteristics of the vocal tract are altered. The length of participants' teeth was augmented by asking them to wear an acrylic prosthesis. Participants were asked to produce / s / when feedback was available and when it was not. The results demonstrate that the degree to which a new vocal tract configuration is learned is directly related to quality of auditory feedback.;Taken together, these studies have implications for the understanding of speech motor control as well for motor control in general. The results shed light on the conditions in which feedback modifies and how it may be integrated into internal models that are the basis of motor planning and control.