Auditory cortical and brainstem response dynamics in quiet and noise amongst unilaterally deaf adults with and without tinnitus.

Objective: Cortical auditory evoked potentials (CAEPs) and Auditory Brainstem Responses (ABRs) elicited by sounds in quiet and in noise were compared between unilaterally deaf adults with and without associated tinnitus (UD+T and UD-T). CAEP amplitudes were hypothesised to primarily vary with absolute stimulus levels in UD+T listeners rather than signal-to-noise ratio (SNR), whereas ABR amplitudes would reflect both level and SNR regardless of tinnitus status.

Methods: Responses were recorded at 60 and 45 dB nHL with white noise set to give 0 and +10 dB SNR. Participants were 8 UD-T, 13 UD+T listeners, and 13 binaurally hearing controls.

Results: The UD-T group CAEP amplitudes showed an additive effect of stimulus level (p = 0.025) and SNR (p = 0.002) while UD+T and control listeners showed only the effect of SNR (p = 0.004). ABR amplitudes reflected the additive effects of level and SNR in all groups.

Conclusions: The primary determinant of CAEP amplitudes to signals in noise is SNR not stimulus level. This effect was not apparent in UD-T listeners, whose amplitudes were determined by both level and SNR, similarly to the brainstem potentials.

Significance: The findings suggest altered processing of neural noise in unilaterally deaf adult listeners without tinnitus.