Robert V. Shannon
Fan-Gang Zeng
House Ear Inst., 2100 W. Third St., Los Angeles, CA 90057
Psychophysical results in gap detection, forward masking, temporal integration, and modulation detection have been obtained in electrically stimulated listeners (both cochlear implant and brain-stem implant) as a function of stimulus intensity. The results indicate that temporal processing is similar in normal-hearing and implant listeners when the intensity scale is normalized. Recent loudness balancing and intensity discrimination experiments have demonstrated that loudness is coded by dual mechanisms depending on stimulus frequency. The loudness of low-frequency (<300 Hz) electrical stimuli is a power-law function of electrical amplitude and the mechanism is inferred to reside in the cochlear nucleus. In contrast, loudness of high-frequency stimuli is an exponential function of electrical amplitude with a more peripheral mechanism. By comparing temporal processing at low and high frequencies the processing order of loudness and timing information in the auditory system can be inferred. [Supported by NIH/NIDCD.]