Background: Pure-tone audiometry and otoacoustic emissions (OAEs) are the standard clinical hearing tests to evaluate hearing thresholds and outer-hair-cell (OHC) damage, respectively. However, these tests are insensitive to supra-threshold hearing deficits or auditory-nerve fiber loss [i.e., cochlear synaptopathy (CS)]. Since this pathology can hide behind a normal audiogram and OAEs, CS is known as "hidden hearing loss". Hitherto, animal studies and simulations using computational model of the auditory periphery have shown that supra-threshold auditory evoked potentials (AEPs) and speech intelligibility in background noise (SPIN) are promising measurements to assess CS in humans. Despite the recent progress in diagnostic CS markers, the relation between SPIN and AEPs has not yet been thoroughly investigated. This study incorporates CS-sensitive EEG markers into an auditory profile that was applied to a large group of aging participants to quantify age-related CS and its relation to speech recognition.

Method and results: A total of 69 Flemish subjects were tested with the test battery including questionnaires, pure tone audiometry (PTA) at conventional and extended high frequencies (EHFs), distortion product OAE (DPOAE), SPIN and AEP measurements [e.g., auditory brainstem response (ABRs) and envelope following responses (EFRs)]. Participants were divided into three groups: (i) young normal-hearing adults (18-25 years), (ii) normal hearing adults who complain of tinnitus or reduced speech intelligibility in noise (18-60 years), but have a normal audiogram and (iii) hearing impaired adults (18-60 years). We explored the effect of age, hearing sensitivity and self-reported hearing/tinnitus complaints on potential biomarkers of CS (e.g., EFR magnitude, ABR wave-I and V amplitudes) and speech reception thresholds, and studied their relation to metrics which are sensitive to OHC-loss (e.g., hearing thresholds and DPOAEs). We found that the EFR reductions observed in the older groups is consistent with age-related CS, but that it remains challenging to parse out the role of extended high- frequency hearing loss and CS to predict speech-recognition declines. We conclude that early markers of SNHL (EFRs or extended high frequency thresholds) are crucial for a timely diagnosis of speech intelligibility problems with age.

Funding: Work supported by ERC STG 678120 and ERC POC 899858.