Our ability to evaluate the role played by reflex pathways in the control of either normal or abnormal speech movements is limited by lack of knowledge of basic physiological properties of oral motor reflexes and the difficulty of designing experiments that would allow a quantitative assessment of inputs arising over these pathways. Recently, through a collaborative effort involving investigators from the disciplines of speech physiology and neurophysiology, noninvasive methods have been developed to assess the reflex effects of low-level cutaneous, auditory, and stretch stimuli on the jaw-closing muscles of humans. Reflex responses are measured, not only as changes in jaw-closing muscle activity, but as fluctuations in jaw-closing force. Precisely specified stimuli are delivered to the oral system while well-controlled background conditions are maintained. Using these methods, experiments in the present proposal have been designed (1) to describe the effects on the jaw-closing muscles of humans of low-level cutaneous, auditory, and stretch stimuli presented singly and in close temporal proximity, (2) to compare properties of reflexes elicited under static conditions to characteristics of the individual's neuromotor output during speech, and (3) to determine if the amplitude of oral motor reflexes is significantly modulated prior to speech production. These investigations will have significant implications for understanding the organization of oral motor systems in normal human subjects. They may also contribute to our understanding of the concept of """"""""reflex"""""""" and to the question of whether reflexes should be viewed as a potentially important factor indisordered speech production.
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