Behavioral Estimates of the Contribution of Inner and Outer Hair Cell Dysfunction to Individualized Audiometric Loss
Differentiating the relative importance of the various contributors to the audiometric loss (HLTOTAL) of a given hearing impaired listener and frequency region is becoming critical as more specific treatments are being developed. The aim of the present study was to assess the relative contribution of inner (IHC) and outer hair cell (OHC) dysfunction (HLIHC and HLOHC, respectively) to the audiometric loss of patients with mild to moderate cochlear hearing loss. It was assumed that HLTOTAL = HLOHC + HLIHC (all in decibels) and that HLOHC may be estimated as the reduction in maximum cochlear gain. It is argued that the latter may be safely estimated from compression threshold shifts of cochlear input/output (I/O) curves relative to normal hearing references. I/O curves were inferred behaviorally using forward masking for 26 test frequencies in 18 hearing impaired listeners. Data suggested that the audiometric loss for six of these 26 test frequencies was consistent with pure OHC dysfunction, one was probably consistent with pure IHC dysfunction, 13 were indicative of mixed IHC and OHC dysfunction, and five were uncertain (one more was excluded from the analysis). HLOHC and HLIHC contributed on average 60 and 40 %, respectively, to the audiometric loss, but variability was large across cases. Indeed, in some cases, HLIHC was up to 63 % of HLTOTAL, even for moderate losses. The repeatability of the results is assessed using Monte Carlo simulations and potential sources of bias are discussed.
Keywordshearing loss cochlear nonlinearity temporal masking curves forward masking basilar membrane hearing aid Monte Carlo simulations
We thank Santiago Santa Cruz for his help with subject recruitment. We are grateful to the associate editor, Barbara Shinn-Cunningham, and three anonymous reviewers for their excellent suggestions on earlier versions of this manuscript. Work supported by The Oticon Foundation and by the Spanish Ministry of Innovation and Science (grants BFU2006-07536 and BFU2009-07909). Portions of this work were presented at the 33 rd Midwinter Meeting of the Association for Research in Otolaryngology, 6–10 February 2010, Anaheim, CA, USA, and at the 159th Meeting of the Acoustical Society of America, 19–23 April 2010, Baltimore, MD, USA.
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