CLINICAL MEASURES OF AUDITORY LINEAR/NONLINEAR PROCESSES

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A common finding in clinical audiology is that hearing-impaired listeners with similar configurations and degrees of hearing loss perform differently on measures of speech perception. Consequently, these people may differ in the benefits they receive from amplification. One reason for the lack of homogeneity among hearing-impaired listener is that the audiogram provides only a rough estimate of cochlear pathology. Thus, it is possible that hearing-impaired listeners differ in their underlying cochlear pathology and measures of pure-tone threshold lack the sensitivity to distinguish these individuals. Cochlear pathology alters cochlear transduction processes. Mechano- electric and electro-mechanic transduction processes are modified, either directly through changes in hair cell structure, or indirectly, through structures on which hair cell transduction relies. An objective measure that characterizes these processes will describe the physiologic consequences of cochlear disorders and supply a more accurate description of sensorineural hearing loss then presently available. A clinical measure of cochlear transduction could lead to a new categorization scheme of sensorineural hearing loss based on the underlying pathophysiology. The long term goal of this research is to use such a scheme to determine if the underlying physiologic changes in the cochlea can account for the variation between hearing-impaired listeners on functional measures of hearing, and design new signal processing algorithms for hearing aids. Cochlear transduction processes are inherently nonlinear, therefore, a measure of cochlear transduction must be sensitive to nonlinear processes. Auditory distortion products are indices of nonlinearity and reflect cochlear integrity, but their absence only indicates a change in transduction, not a description of the altered transduction processes. A new nonlinear systems identification procedure developed by Bendat (1990) can be used to characterize cochlear transduction processes across a broad range of frequencies. This technique can be applied to ECochG, AEPs, and OAEs, thus, both mechano-electric and electro-mechanic transduction processes in the cochlea can be described. The special goal of this investigation is to use Bendat's procedure to develop a measure of cochlear transduction, quantify the reliability of the measure, and determine its sensitivity to changes in cochlear physiology due to cochlear damage.