On the Interplay between Cochlear Gain Loss and Temporal Envelope Coding Deficits

Sarah Verhulst, Patrycja Piktel, Anoop Jagadeesh, Manfred Mauermann

Hearing impairment is characterized by two components: (i) cochlear gain loss that yields wider auditory filters and elevated hearing thresholds, and (ii) cochlear neuropathy, a noise induced aspect of hearing loss that may impact temporal coding fidelity of supra-threshold sound. This study uses a psychoacoustic amplitude modulation (AM) detection task in quiet and multiple noise backgrounds to test whether these aspects of hearing loss can be isolated in listeners with normal to mildly impaired hearing ability. Psychoacoustic results were correlated to hearing threshold, categorical loudness scaling, distortion product otoacoustic emission (DPOAE) thresholds and envelope-following response (EFR) measures. AM thresholds to noise carriers (4 kHz octave-wide) depended on DPOAE thresholds and associated cochlear compression levels. The amount with which wideband masking noise (1 octave) worsened 4 kHz pure-tone AM thresholds was inversely correlated to DPOAE thresholds in correspondence to a compression loss benefit, while the amounts with which narrowband noise maskers (40 Hz) worsened performance was not. While the latter condition was designed to reduce temporal coding ability within an auditory filter, the correlation with the EFR measures was weak. This study elucidates how psychoacoustic difference measures can be adopted in the differential diagnostics of hearing deficits in listeners with mixed pathologies.