Tinnitus and Speech-in-Noise Performance in Normal Hearing

A new study has found that normal-hearing adults with tinnitus show reduced action potential amplitudes in a specific electrocochleography test. This measure also correlated with speech-in-noise performance in people without tinnitus, suggesting a shared peripheral mechanism may underlie both issues.

Connecting Tinnitus and Hearing in Noise

For years, researchers have suspected a common thread between tinnitus and difficulty understanding speech in noisy environments. The leading candidate is cochlear synaptopathy, often called “hidden hearing loss.” This condition involves damage to the synapses connecting inner hair cells to the auditory nerve, which can occur without affecting the thresholds on a standard audiogram. This study, led by Tzu-Yuan Wang and colleagues, directly investigated this link by measuring peripheral nerve function and real-world listening performance in one test session.

How the Study Measured Nerve Function and Listening

The researchers recruited 20 adults with chronic, nonpulsatile tinnitus and 20 age-matched controls without tinnitus. All participants had clinically normal hearing.

The core test was chirp-evoked electrocochleography (ECochG). Unlike a standard click stimulus, a chirp sound is designed to synchronize the response from hair cells along the entire cochlea, potentially providing a more complete picture of cochlear health. The team measured the action potential (AP)—the electrical response of the auditory nerve—in two ways: from the peak to the baseline (AP1) and from the peak to the subsequent trough (AP2).

Participants also completed a speech-in-noise (SPIN) test under multiple conditions that simulated challenging real-world listening, such as speech with competing talkers or background babble.

A Specific Neural Deficit in Tinnitus

The results revealed a clear, specific difference. While chirp stimuli produced larger AP1 responses than clicks in all participants, the key finding was in the AP2 measure. The tinnitus group exhibited significantly reduced chirp-evoked AP2 amplitudes compared to the control group. This suggests a possible deficiency in synchronized neural firing in the auditory nerve of individuals with tinnitus, despite their normal pure-tone hearing.

Perhaps more telling was the relationship found in the control group. Here, researchers observed a significant correlation between AP2 amplitude and SPIN performance, but only under the most difficult listening condition. Individuals with larger AP2 amplitudes performed better at understanding speech in intense noise. This link was not found in the tinnitus group, a nuance the authors suggest may point to additional central processing factors at play once tinnitus is present.

What AP2 Might Represent

The AP2 amplitude, measured from peak to trough, is thought to reflect the synchrony and strength of the neural response from a broad population of auditory nerve fibers. A reduced amplitude could indicate fewer fibers firing or less coordinated firing—the hallmarks of synaptopathy. The fact that this measure also predicted noise-handling ability in controls strengthens the argument that it is capturing a functionally important aspect of peripheral hearing health.

Practical Implications for Assessment and Understanding

This research has direct implications for how hearing issues are evaluated. It proposes a dual-assessment model combining an objective physiological test (chirp-evoked ECochG) with a subjective perceptual test (challenging SPIN). Together, these could offer a more complete profile than either test alone, particularly for patients with complaints that seem disproportionate to their audiogram.

For clinicians and patients, the study reinforces that “normal hearing” on an audiogram does not guarantee perfect auditory function. Complaints of tinnitus and struggling in noisy restaurants may have a genuine biological basis in the peripheral auditory system. This validation can be an important step in a patient’s journey, moving the discussion toward management and coping strategies. For instance, approaches like sound therapy or cognitive behavioral techniques can be tailored with this understanding in mind.

The findings also add a piece to the larger puzzle of auditory processing. They align with research showing how hearing loss alters brain connectivity, suggesting problems may start in the cochlea and cascade upward. Furthermore, it highlights the ongoing search for objective biomarkers for auditory disorders, a pursuit also seen in work on biomarkers for tinnitus.

A Step Toward Better Auditory Profiles

The study by Wang et al. moves the field forward by providing a method to investigate cochlear synaptopathy in living humans. As the authors note, histopathological confirmation is impossible in living patients, so these noninvasive measures are essential. The reduced AP2 amplitude in the tinnitus group and its functional correlation in controls offer compelling, if indirect, evidence for synaptopathy as a contributor to these common auditory complaints.

This work suggests future hearing health assessments may routinely include measures of neural heath, not just hair cell sensitivity. For the millions with tinnitus and hearing-in-noise difficulties, it brings clearer diagnostic insight and a stronger scientific foundation for future treatments.

Source: Wang TY, Chen YF, Chen CK, Chang CT. Chirp-Evoked Electrocochleography and Speech-in-Noise Performance in Normal-Hearing Individuals With Tinnitus. J Speech Lang Hear Res. 2026.