Abstract
Recent physiological studies in animals showed that noise-induced sensorineural hearing loss (SNHL) increased the amplitude of envelope coding in single auditory-nerve fibers. The present study investigated whether SNHL in human listeners was associated with enhanced temporal envelope coding, whether this enhancement affected pitch discrimination performance, and whether loss of compression following SNHL was a potential factor in envelope coding enhancement. Envelope processing was assessed in normal-hearing (NH) and hearing-impaired (HI) listeners in a behavioral amplitude-modulation detection task. Fundamental frequency difference limens (F0DLs) were obtained in the same listeners for complex tones with varying harmonic resolvability. Basilar-membrane input/output functions were measured to assess individual compression ratios. For NH listeners, F0DLs decreased with increasing harmonic resolvability. For the unresolved conditions, all five HI listeners performed as good as or better than NH listeners with matching musical experience. Two HI listeners showed lower amplitude-modulation detection thresholds than NH listeners for low modulation rates, and one of these listeners also showed a loss of cochlear compression. Overall, these findings suggest that some HI listeners may benefit from an enhancement of temporal envelope coding in pitch discrimination of unresolved complex tones, and that this enhancement may be also ascribed to a reduction of cochlear compression following SNHL.
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