Dead regions in the cochlea: conceptual foundations, diagnosis, and clinical applications.

Regions in the cochlea with no (or very few) functioning inner hair cells and/or neurons are called "dead regions". This paper reviews the anatomical, physiological, and psychophysical foundations for the concept of dead regions. It then considers methods that have been used to diagnose dead regions, focusing particularly on psychophysical tuning curves and the test using threshold-equalizing noise. Problems and limitations of each approach are discussed. Applications of tests for diagnosing dead regions are described. These include: giving the client realistic expectation about the likely benefit of a hearing aid; guidance in the fitting of hearing aids; assessment of candidacy for cochlear implants; assessment of hearing loss for medico-legal applications. Finally, guidelines for implementation of the threshold-equalizing noise test in clinical practice are given.