POSSIBLE APPLICATION OF FUNCTIONAL IMAGING OF THE HUMAN AUDITORY-SYSTEM IN THE STUDY OF ACCLIMATIZATION AND LATE-ONSET DEPRIVATION

After some period of experience with a single hearing aid, speech reco gnition performance may increase for material presented to the aided e ar. Conversely, performance may decline for material presented to the unaided ear. Improved performance for the normally aided ear beyond th at observed at the initial fitting of the hearing aid has been describ ed as the acclimatization effect. The decline in speech recognition fo r material presented to the unaided ear has been described as the late onset auditory deprivation effect. For both the acclimatization and d eprivation effects, the observed changes in performance are not consid ered to be a consequence of a change in the functional status of the c ochlea, Rather, the benefits and decrements in speech recognition perf ormance presumably reflect functional changes or reorganization in the central auditory pathway. In nonhuman species, changes in central aud itory function can be examined by physiological recordings directly fr om various structures along the auditory pathway. However, these techn iques are invasive and inappropriate for studying possible changes in central function for the human auditory system. The purpose of this re view is to describe noninvasive ''imaging'' techniques appropriate for use with human subjects and the ways they could be applied to objecti vely identify physiological changes that might be associated with eith er acclimatization or late onset deprivation effects. Currently, few o f these techniques have been applied to the study of acclimatization a nd late onset auditory deprivation. Possible application of these tech niques to assess the differential performance changes for material pre sented to the normally aided and normally unaided ear will be discusse d.