Associations between extended high-frequency thresholds and middle ear muscle reflex growth functions in adults with normal audiograms

Objectives: – Understanding the relationship between extended high-frequency (EHF) hearing and middle ear muscle reflex (MEMR) function may clarify how variations in cochlear health affect auditory reflexes, providing insight into subclinical auditory deficits and potential early markers of hearing loss. In this study, the authors examined whether elevated EHF thresholds are associated with reduced MEMR growth in adults with clinically normal audiograms. The authors hypothesized that individuals with higher EHF thresholds would exhibit shallower MEMR growth functions despite normal thresholds in the conventional frequency range. Design: – Eighty-three young adults (aged 18 to 34 years; 166 ears) completed audiometric testing, lifetime noise exposure assessment using the Noise Exposure Structured Interview, tympanometry, and ipsilateral MEMR measurements. MEMR thresholds and growth functions were measured using a broadband noise elicitor and modeled using both linear and segmented regression approaches. Linear mixed-effects models examined associations between standard and EHF hearing thresholds and MEMR outcomes, controlling for covariates. Results: – Age, but not lifetime noise exposure, was significantly associated with elevated EHF thresholds (p < 0.001). Neither standard frequency nor EHF thresholds were significantly related to MEMR thresholds. However, poorer EHF sensitivity was associated with significantly shallower MEMR growth functions, indicating reduced reflex strength in ears with EHF loss despite a clinically normal audiogram. Segmented regression revealed clear MEMR growth function breakpoints in both groups, with the EHF loss group showing a lower breakpoint and overall shallower growth. No significant effects of noise exposure were observed for MEMR threshold and slope. Conclusions: – In young adults with clinically normal audiograms, elevated EHF thresholds were associated with shallower MEMR growth, while MEMR thresholds were relatively insensitive to variation in EHF hearing. As MEMR has been used to infer cochlear synaptopathy, these findings indicate that subclinical differences indexed by EHF hearing are significantly associated with MEMR growth characteristics. This pattern suggests that MEMR changes may not uniquely reflect synaptopathy but may also arise from basal cochlear influences.