Click-evoked otoacoustic emissions and the influence of high-frequency hearing losses in humans

Click-evoked otoacoustic emissions (cEOAEs) are thought to reflect the presence of highly tuned mechanisms involved in sound processing inside the cochlea. When the sensitivity and tuning of the inner ear are impaired in some frequency range, the spectral components of cEOAEs in the same frequency range are expected to be altered if the previous premise is correct. Although clinical experience does not contradict such an interpretation, fundamental aspects of cEOAE generation and propagation in the cochlea are not clear enough to preclude possible additional influences of remote cochlear places on cEOAE. In order to analyze this possibility, ultra-high-frequency hearing thresholds between 8 and 16 kHz were assessed in 43 human subjects that had clinically normal hearing thresholds in the frequency range of cEOAEs. The magnitude of their cEOAEs was found to be correlated to their average ultra-high-frequency hearing threshold, especially when ears presenting spontaneous otoacoustic emissions were not taken into account ($\text{p=0.002,}$ $r^2\text{=0.29}$ ). Age and ultra-high-frequency hearing thresholds were correlated ($\text{p<0.01,}$ $r^2\text{=0.40}$ ); thus it is not possible to exclude that aging was the primary cause of the observed trend. The contribution of ultra-high-frequency hearing status to cEOAE magnitude, perhaps in relation to age, seems to explain a significant part of the variance of “normative” emission data and may be of interest for early detection of high-frequency hearing impairments.