Psychophysical-Tuning Curves and TEN Test in Normal-Hearing Individuals with Tinnitus

Introduction: Studies have shown that individuals with tinnitus show worse speech-in-noise test results than do individuals without tinnitus. An overall reduction in OAE levels has also been reported in the former group of individuals, confirming the presence of outer hair cell dysfunction. Recently, some studies reported inner hair cell dysfunction and dysfunction of the adjacent neurons in such individuals. The possibility that tinnitus is related to cochlear changes, specifically impaired hair cell function, led us to hypothesize that among individuals with normal auditory thresholds, the mechanism of frequency selectivity might differ between subjects with and without tinnitus.

Objective: 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-equalizing noise (TEN) test results.

Methods: We determined PTCs and performed the TEN test. We evaluated 57 individuals, 16 with bilateral tinnitus, and 41 without tinnitus.

Results: PTCs results show a pattern difference between the two groups, characterized by statistical differences at the tails of the curves regarding the following: 2 kHz and 3 kHz PTCs obtained in noise at 6 kHz and 8 kHz; 4 kHz PTCs obtained in noise at 2 kHz and 8 kHz; and 6 kHz and 8 kHz PTCs obtained in noise at 2 kHz and 3 kHz. TEN test revealed differences between groups in terms of auditory thresholds, which were significantly higher in the tinnitus group.

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.