This project will utilize psychophysical techniques to examine basic mechanisms, and relevance to clinical issues, of sensory adaptation to a tactile stimulus. Flutter-vibration stimuli will be used, because it is known that vibrotactile adaptation is largely a central (CNS) process. Seven series of experiments are proposed. In three of these, different aspects of adaptation will be explored in persons with orofacial sensory dysfunctions (patients with temporomandibular disorders, and individuals with nerve damage resulting from mandibular surgery), as well as in normal control subjects. Stimuli will be presented under computer control to the affected region of patients, and to corresponding regions in control subjects. All psychophysical measurements will be made with forced-choice procedures. On the basis of the clinical literature, and current views of cortical dynamics, it is predicted that abnormalities of adaptation will be associated with both clinical conditions. The three aspects of adaptation to be studied are: (1) elevation in absolute vibrotactile threshold; (2) reduction in vibrotactile difference threshold; and (3) the spread of vibrotactile adaptation between locations on the skin. Four additional series of experiments, with normal subjects will provide detailed information about psychophysical mechanisms underlying adaptation. The questions addressed are: (1) What overall patterns of change occur in the perception (loudness and pitch) of vibrotactile stimuli representing a wide range of amplitudes and frequencies, as a result of a given set of adapting conditions?; (2) How do adaptation-induced changes in vibrotactile difference thresholds relate to simultaneously occurring changes in the perceived loudness and pitch of the stimuli?; (3) When a series of short adapting stimuli differing in amplitude are presented, how do their effects combine to regulate vibrotactile adaptation level?; and (4) When two vibrotactile adapting stimuli differing in frequency are presented simultaneously, what principles determine their combined effectiveness? Taken together, the experiments in this project should permit a more unified understanding of vibrotactile adaptation than currently exists.
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