Auditory reflexes are drawing attention as potential indicators of hidden hearing problems, such as cochlear synaptopathy, in which the synapses between hair cells and the auditory nerve are damaged but the standard audiogram remains normal. The middle-ear muscle reflex (MEMR) is considered a marker of such damage, while the medial olivocochlear reflex (MOCR) is linked to speech intelligibility in noise. However, measurements are affected by age, audiometric thresholds, and co-activation of both reflexes. This work stands somewhat apart: its closest neighbors in the archive study cochlear biomechanics, phase sensitivity of hearing, brain reorganization in Alzheimer's disease, the role of vowels in shaping the head's acoustic field, age-related brain changes, predicting nerve stimulation efficacy from EEG, unsupervised learning for brain signals, and recognition of unfamiliar sounds. None of these works directly addresses the middle-ear and olivocochlear reflex arcs, so this study fills a gap in understanding how age and hearing loss affect these reflexes.
The researchers recruited three groups: 20 young people with normal hearing (21–35 years), 14 middle-aged people with normal hearing (46–62 years), and 17 middle-aged people with hearing loss (47–65 years). Normal hearing was defined as thresholds no higher than 20 dB HL at all standard frequencies. To assess cochlear status, they measured distortion-product otoacoustic emissions (DPOAE), which reflect outer hair cell function, and the envelope-following response (EFR), considered a marker of synaptopathy. The middle-ear reflex was measured in two ways: the traditional clinical method with a 226 Hz tone and a broadband method with 94 µs clicks at 90 dB peSPL. The olivocochlear reflex was assessed by the change in click-evoked otoacoustic emissions (CEOAE) during presentation of a noise elicitor at 60 and 75 dB SPL. To detect contamination from the middle-ear reflex, they analyzed the first 2 ms of the click response, where the mechanical muscle reaction should appear.
Middle-ear reflex: thresholds did not differ between groups, but amplitude at 90 dB SPL was significantly lower in older people with normal hearing compared with young people (g = 0.61, p = .038). After adjusting for DPOAE, this difference disappeared, and adjustment for extended high-frequency thresholds (EHF) reduced it even further. This points to a link between reflex amplitude and subclinical cochlear damage, not age as such. Olivocochlear reflex: at low frequencies there was no age effect, but there was a difference between older people with normal hearing and those with hearing loss (g = 0.80, p = .015), which vanished after adjusting for DPOAE. At high frequencies, the age effect was significant (g = 0.60, p = .016) and persisted after adjustments for DPOAE and EFR, but disappeared after adjusting for high-frequency audiometric thresholds. Contamination from the middle-ear reflex: at an elicitor level of 75 dB SPL, 66.7% of young people and 50% of older people with normal hearing showed MEMR activation during MOCR measurement. The difference in click response over the first 2 ms was significantly larger at 75 dB (M = 0.051, SD = 0.0871) than at 60 dB (M = 0.003, SD = 0.0110; t(15) = -2.37, p = .031, d = -0.59). This marker correlated strongly with separately measured MEMR amplitude at 75 dB (r = .92, p < .001).
The work shows that middle-ear reflex amplitude is sensitive to subclinical cochlear damage that is invisible on a standard audiogram but shows up in extended high frequencies and DPOAE. This supports the idea of using MEMR as a marker of hidden hearing loss, although the link to synaptopathy via EFR was not confirmed. The olivocochlear reflex turned out to be resistant to subclinical cochlear changes but sensitive to audiometric thresholds, which matters for interpreting its role in speech perception in noise. The main methodological achievement: a simple way to detect MOCR contamination from MEMR using the first 2 ms of the response, which improves the reliability of future studies. Unlike neighboring works focused on individual links of the auditory system (cochlear biomechanics, phase sensitivity, brain signals), this study connects peripheral reflexes to age-related and pathological changes using multilevel correction for sensorineural markers.
The topic could move toward more frequency-specific elicitors for the middle-ear reflex to link it to damage in specific cochlear regions. For the olivocochlear reflex, it would be promising to study how the response depends on elicitor level in people with sloping high-frequency hearing loss. It is also necessary to develop objective criteria for excluding MEMR contamination during MOCR measurement, possibly with automatic analysis of the first milliseconds of the response.
The results will affect clinical audiology, where the middle-ear reflex is used for diagnosis, and research on hidden hearing loss, where clean olivocochlear reflex measurements are crucial.
Conduct measurements with frequency-specific MEMR elicitors and compare them with EFR at the same frequency. Investigate the growth of MOCR function at different elicitor levels in people with hearing loss to determine optimal parameters without MEMR contamination.
The work is directly related to the problem of hidden hearing loss (cochlear synaptopathy), which is not detected by standard audiometry. The lack of correlation between MEMR and EFR raises the question of how much these markers reflect the same pathophysiological process. Also unresolved is the problem of separating the contributions of afferent and efferent pathways to reflex responses, which is critical for diagnosing retrocochlear lesions.
The middle-ear reflex fires not only in response to external loud sounds but also to your own vocalizations: when a person speaks or sings, the muscle tenses to protect the cochlea from excessive stimulation.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.