In recent years, psychophysicists have demonstrated that the temporal processing capabilities of listeners with sensorineural hearing loss are impaired in terms of temporal summation, temporal resolution and temporal masking. Although the temporal changes have been documented psychophysically in humans, little is known about the underlying neural and anatomical pathologies. Therefore, the goal of this project is to determine what changes occur in the temporal response patterns of single auditory nerve fibers during conditions of noise-induced temporary or permanent threshold shift, and to relate the changes in neural performance to the underlying cochlear pathologies. The effects of noise-induced hearing loss on temporal processing will be evaluated psychophysically in chinchillas by measuring gap detection thresholds, threshold-duration functions for tones and forward masking functions using an iso-response technique. These measures will provide a behavioral index of changes in temporal resolution, temporal summation and short-term adaptation. Single unit measurements in the auditory nerve will be carried out that parallel or compliment the psychophysical studies, i.e., test stimuli similar to those used in the psychophysical experiments will be used to study the response of populations of single auditory nerve fibers in normal and noise-exposed animals. Some of the neural measures of interest include phase locking to tones and noise gaps, comparison of the onset and steady-state discharge rates to tone bursts to estimate neural adaptation and the recovery of neural sensitivity following a "masking" stimulus; these neural measures can be related to other neural measures such as tuning, threshold and spontaneous activity, as well as to the psychophysical performance changes noted above. Cochleas from the noise-exposed animals will be processed to determine if the temporal processing changes are related to specific cochlear pathologies or patterns of hair cell loss. The results are potentially important for understanding the basic mechanisms undelying temporal processing in hearing. It may be possible for more sophisticated hearing aids of the future to compensate for these changes in temporal processing.