Murat Erinc, Ufuk Derinsu
Marmara University, School of Medicine, Audiology Department
Background: Tinnitus and hyperacusis are widely assumed to be associated with the central gain mechanism, and this mechanism also has control over loudness perception. Although central gain increases with the attempts to compensate hearing loss, reduced input can also be observed in those with clinically normal hearing. This study aimed to evaluate the loudness growth function of tinnitus patients with and without hyperacusis using behavioral and electrophysiological methods.
Methods: The study consists of 3 groups with a total of 60 clinically normal hearing subjects, including the control group (10 men and 10 women; mean age, 39.8; SD, 11.8 years), tinnitus group (10 men and 10 women; mean age, 40.9; SD, 12.2 years) and hyperacusis group (also have tinnitus) (7 men and 13 women; mean age, 38.7; SD, 14.6 years). Loudness discomfort levels (LDLs), categorical loudness scaling (CLS), and auditory cortical evoked potentials (ACEP) were used for the evaluation of loudness growth. N1-P2 component amplitudes and latencies were measured.
Results: LDL results of 500, 1000, 2000, 4000, and 8000 Hz showed a significant difference between the hyperacusis group and the other two groups (p <0.001). In the loudness scale test performed with 500 Hz and 2000 Hz narrow-band noise (NBN) stimulus, a significant difference was observed between the hyperacusis group and the other two groups in the “medium,” “loud,” and “very loud,” categories (p <0.001). In the cortical examination performed with 500 Hz and 2000 Hz NBN stimulus at 40, 60, 80 dB nHL intensities, no significant difference was observed between the groups in the N1, P2 latency and N1-P2 peak-to-peak amplitude.
Conclusion: The hyperacusis group is significantly different between the groups in behavioral tests, but not in electrophysiological tests. In our attempt to determine hyperacusis with objective tests, N1 and P2 response was not seen as a suitable method. However, CLS can also be used in addition to LDLs used in behavioral tests.