Auditory cortical and brainstem response dynamics in quiet and noise amongst unilaterally deaf adults with and...

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.

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.

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.

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.

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