Sarineh Keshishzadeh1, Heleen Van Der Biest2, Sarah Verhulst1
1Dept. of Information Technology, Ghent University, 9000 Ghent, Belgium
2Dept. of Rehabilitation Sciences–Audiology, Ghent University, 9000 Ghent, Belgium
Even though age-induced cochlear synaptopathy (CS) has been demonstrated in rodent and human temporal bones, it remains challenging to determine whether this pathology causes speech intelligibility declines. Difficulties in studying the causality of this relationship in humans relate to the necessity to use indirect and non-invasive (often EEG-based) markers of CS. To study the relationship between speech intelligibility and CS in the ageing population, we adopted low- and high-pass filtered speech conditions (Flemish Matrix test in quiet and noise), alongside an extended hearing screening battery that comprised distortion-product otoacoustic emissions, auditory brainstem responses (ABRs), envelope-following responses (EFRs) and extended high-frequency thresholds (EHFTs).
A total of 69 Flemish subjects participated in this study and were divided into two groups: (i) a young control group with normal audiograms (18-25 years) and (ii) Older adults with a normal audiogram, some with complaints of tinnitus or self-reported speech intelligibility problems (45-60 years). We compared our results to a German cohort of 45 listeners that included older participants as well to study how hearing sensitivity, EHFTs and potential biomarkers of CS (EFRs and ABRs) changed as a function of age. The EFR reductions observed in the older group is consistent with age-related CS, and EFR markers were more sensitive to detect individual differences than were ABR markers. At the same time, it remains challenging to determine whether EHF hearing or CS is more important in predicting individual speech intelligibility declines. Based on the model simulations, our EFR marker was only marginally sensitive to outer hair cells deficits, and hence we believe that CS plays an important functional role even though both EHFTs and EFRs were affected by the aging process. We conclude that early markers of sensorineural hearing loss (EFRs or EHFTs) are crucial for a timely diagnosis of speech intelligibility problems with age.
Acknowledgements: This work was supported by the European Research Council (ERC) under the Horizon 2020 Research and Innovation Programme (grant agreement No 678120 RobSpear and No 899858 CochSyn).