Psychoacoustic analyses of cochlear mechanisms in tinnitus patients with normal auditory thresholds

Abstract

Objective: Tinnitus is often related to auditory dysfunction. We hypothesised that, among individuals with normal auditory thresholds, the mechanism of frequency selectivity might differ between subjects with and without tinnitus. Our objective was to identify any differences between normal-hearing individuals with tinnitus and those without in terms of psychophysical tuning curves (PTCs) and threshold-equalising noise (TEN) test results. Design: We determined PTCs and performed the TEN test. Study sample: We evaluated 57 individuals, 16 with bilateral tinnitus (tinnitus-group) and 41 without tinnitus (control-group). Results: We found significant differences between tinnitus and control groups regarding the following: 2 kHz PTCs obtained in noise at 6 and 8 kHz; 4 kHz PTCs obtained in noise at 2 and 8 kHz; and 6 and 8 kHz PTCs obtained in noise at 2 and 3 kHz. The TEN test revealed differences between groups in terms of auditory thresholds, which were significantly higher in the tinnitus group. In addition, none of the individuals in the tinnitus group were found to have dead regions in the cochlea. Conclusions: Despite having normal auditory thresholds, individuals with tinnitus have auditory patterns that differ significantly from those seen in individuals without tinnitus, such differences being suggestive of cochlear impairment.