Chirp-Evoked Electrocochleography and Speech-in-Noise Performance in Normal-Hearing Individuals With Tinnitus

Both tinnitus and poor hearing-in-noise performance have been proposed as perceptual consequences of cochlear synaptopathy, which can occur in the absence of significant hearing loss. However, to date, no study has investigated chirp-evoked electrocochleography (ECochG) measures or examined the relationship between action potential (AP) amplitude and speech perception in noise (SPIN) performance in normal-hearing individuals with tinnitus.

Twenty participants with nonpulsatile tinnitus lasting at least 3 months were recruited for the tinnitus group. An additional 20 age-matched individuals without tinnitus comprised the control group. All participants underwent chirp-evoked ECochG and SPIN testing in the designated ear. AP amplitude was measured using two approaches: from the AP peak to the baseline (AP1) and from the AP peak to the subsequent trough (AP2). SPIN performance was assessed under multiple listening conditions designed to simulate challenging real-world environments.

While chirp-evoked AP1 amplitudes were significantly greater than those elicited by click stimuli, group differences emerged only for chirp-evoked AP2, with the tinnitus group exhibiting reduced amplitudes. Moreover, a significant correlation between chirp-evoked AP2 amplitude and SPIN performance under the most challenging listening condition was observed in the control group, with larger AP2 amplitudes associated with better SPIN performance.

Although cochlear synaptopathy cannot be definitively verified without histopathological examination, the present findings suggest that combining chirp-evoked ECochG with SPIN testing may provide complementary, noninvasive information about auditory function in individuals with and without tinnitus. Together, these measures may provide insight into peripheral and central mechanisms contributing to tinnitus and speech-in-noise perception.