All understanding of neural mechanisms controlling the larynx ad voice is an important health objective for the treatment and prevention of disorders affecting voice and speech. The present proposal will attempt to improve our understanding of the role of auditory feedback on voice pitch control. Normal adults, children, trained singers and adult stutterers will serve as subjects. Subjects will vocalize and receive their own voice through earphones as a source of feedback. The pitch and spectral content of the subject's voice will be experimentally manipulated to learn which aspects of the acoustical feedback signal are most important in the control of the voice pitch. Each variable, voice pitch and spectral content will be systematically and independently manipulated. Linear systems analysis utilizing sinusoidal modulation of voice pitch will be done in order to develop a transfer function of the system controlling voice pitch. Subjects will perform various vocal tasks to learn under which vocal conditions auditory feedback is most important. By learning how and under what conditions altered auditory feedback changes vocal output, we will learn how normal vocal output depends on auditory feedback. Comparison of the responses of normal adults with children will provide information on development on neural mechanisms related to control of voice pitch. Comparisons of responses of normal adults with trained singers will provide information on the limits of control of voice pitch in well trained singers. Comparisons of responses from normal adults with stutterers will provide information that may be important for the understanding of the etiology or treatment stuttering. We wish to test the hypotheses that (1) normal vocalization relies to some extent on auditory feedback, (2) control of voice pitch depends on feedback pitch of the auditory signal, (3) the magnitude of a pitch change in the subject's voice feedback influences the magnitude of a change in vocal output, (4) the more similar the spectral characteristics of the feedback are to the speaker's own voice, the stronger the effect of feedback will be, (5) under certain demanding vocal tasks, auditory feedback is more important than simpler tasks, (6) different subject groups rely more heavily on feedback for the control of voice of than others and (7) susceptibility to feedback interruption may be related to training, development or stuttering. Experiments on mechanical stimulation of laryngeal structures will be conducted in order to learn the most effective means of activating mechanical sensory receptors that reflexively modify laryngeal muscles. Eventually, knowledge from these experiments will be used to test models of neural dysfunction involving sensation in voice disordered patients.
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