Abstract
The goal of this study was to describe the contribution of outer hair cells (OHCs) and the auditory nerve (AN) to speech understanding in quiet and in the presence of background noise. Fifty-three human subjects with hearing ranging from normal to moderate sensorineural hearing loss were assayed for both speech in quiet (Word Recognition) and speech in noise (QuickSIN test) performance. Their scores were correlated with OHC function as assessed via distortion product otoacoustic emissions, and AN function as measured by amplitude, latency, and threshold of the VIIIth cranial nerve Compound Action Potential (CAP) recorded during electrocochleography (ECochG). Speech and ECochG stimuli were presented at equivalent sensation levels in order to control for the degree of hearing sensitivity across patients. The results indicated that (1) OHC dysfunction was evident in the lower range of normal audiometric thresholds, which demonstrates that OHC damage can produce “Hidden Hearing Loss,” (2) AN dysfunction was evident beginning at mild levels of hearing loss, (3) when controlled for normal OHC function, persons exhibiting either high or low ECochG amplitudes exhibited no statistically significant differences in neither speech in quiet nor speech in noise performance, (4) speech in noise performance was correlated with OHC function, (5) hearing impaired subjects with OHC dysfunction exhibited better speech in quiet performance at or near threshold when stimuli were presented at equivalent sensation levels. These results show that OHC dysfunction contributes to hidden hearing loss, OHC function is required for optimum speech in noise performance, and those persons with sensorineural hearing loss exhibit better word discrimination in quiet at or near their audiometric thresholds than normal listeners.
Highlights
It is clear that the audiogram, which is the standard metric of audition in humans, is inadequate in identifying otopathologies that contribute to hearing impairment (Moore, 2002; Makary et al, 2011; Liberman et al, 2016)
auditory nerve (AN) fiber density has been correlated to the wave I amplitude of the auditory brainstem response (ABR) in animal studies where outer hair cells (OHCs) integrity has been preserved (Kujawa and Liberman, 2009; Lin et al, 2011), suggesting that wave I amplitude may be used as a tool to measure AN density
This paper attempted to determine whether ECochG Compound Action Potential (CAP) amplitude, which is synonymous with wave I of the ABR, correlated with SIN
Summary
It is clear that the audiogram, which is the standard metric of audition in humans, is inadequate in identifying otopathologies that contribute to hearing impairment (Moore, 2002; Makary et al, 2011; Liberman et al, 2016) In part, this is because of an incomplete understanding of the cellular basis of decoding complex stimuli, such as speech comprehension in the presence of background noise, and defining the functional roles of cochlear cell types involved in audition may lead to better. OHC function has been described as both a cochlear amplifier (Davis, 1983), where OHCs amplify the passive motion of the basilar membrane (BM), and as a bank of frequency-specific filters that fine tune the acoustic signal (Goldstein et al, 1971; Ruggero, 1994) While these models are correct from a theoretical perspective, translating these functions to a clinical perspective is essential in our understanding of how OHC function contributes to audition. Whether OHCs function as cochlear amplifiers that amplify signals at threshold and/or a series of band-width filters to aid speech recognition in the presence of background noise is unknown
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
