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 recognition performance may increase for material presented to the aided ear. Conversely, performance may decline for material presented to the unaided ear. Improved performance for the normally aided ear beyond that observed at the initial fitting of the hearing aid has been described as the acclimatization effect. The decline in speech recognition for material presented to the unaided ear has been described as the late onset auditory deprivation effect. For both the acclimatization and deprivation effects, the observed changes in performance are not considered to be a consequence of a change in the functional status of the cochlea. Rather, the benefits and decrements in speech recognition performance presumably reflect functional changes or reorganization in the central auditory pathway. In nonhuman species, changes in central auditory function can be examined by physiological recordings directly from various structures along the auditory pathway. However, these techniques are invasive and inappropriate for studying possible changes in central function for the human auditory system. The purpose of this review is to describe noninvasive "imaging" techniques appropriate for use with human subjects and the ways they could be applied to objectively identify physiological changes that might be associated with either acclimatization or late onset deprivation effects. Currently, few of these techniques have been applied to the study of acclimatization and late onset auditory deprivation. Possible application of these techniques to assess the differential performance changes for material presented to the normally aided and normally unaided ear will be discussed.