Cochlear Tuning in Early Aging Estimated with Three Methods.

Age-related hearing loss (ARHL) currently affects over 20 million adults in the U.S. and its prevalence is expected to increase as the population ages. However, little is known about the earliest manifestations of ARHL, including its influence on auditory function beyond the threshold of sensation. This work explores the effects of early aging on frequency selectivity (i.e., "tuning"), a critical feature of normal hearing function. Tuning is estimated using both behavioral and physiological measures-fast psychophysical tuning curves (fPTC), distortion product otoacoustic emission level ratio functions (DPOAE LRFs), and stimulus-frequency OAE (SFOAE) phase gradient delay. All three measures were selected because they have high potential for clinical translation but have not been compared directly in the same sample of ears. Results indicate that there may be subtle changes in tuning during early aging, even in ears with clinically normal audiometric thresholds. Additionally, there are notable differences in tuning estimates derived from the three measures. Psychophysical tuning estimates are highly variable and statistically significantly different from OAE-derived tuning estimates, suggesting that behavioral tuning is uniquely influenced by factors not affecting OAE-based tuning. Across all measures, there is considerable individual variability that warrants future investigation. Collectively, this work suggests that age-related auditory decline begins in relatively young ears (<60 years) and in the absence of traditionally defined "hearing loss." These findings suggest the potential benefit of characterizing ARHL beyond threshold and establishing a gold standard for measuring frequency selectivity in humans.