A cochlear dead region is caused by non-functioning inner hair cells and/or neurons. Sometimes neighbouring hair cells, normally tuned for other frequencies, are able to pick up sounds in a dead region. Clinically, this will present as a threshold on a traditional pure tone audiogram. However, this can be very misleading as this may of course not be the real threshold. It is therefore very difficult to diagnose dead regions by a normal hearing test. The threshold equalizing noise (TEN) test was developed to overcome this problem. TEN measures pure tone thresholds in a special masking noise.
If dead regions are present this may have important implications for fitting hearing aids. There may in fact be little or no benefit from hearing aid amplification well inside the dead region (Moore 2009).A dead region at a particular frequency is indicated when:
Some behaviours that could indicate the presence of a dead region
Once a dead region has been identified, the clinician can then:
Read more about the TEN test in the Threshold Equalizing Noise quick guide: http://www.interacoustics.com/support/ac40/ac40-quick-guides/863-threshold-equalizing-noise-ten/file
Read more about dead regions Moore's article: http://www.hearingreview.com/2010/01/testing-for-cochlear-dead-regions-audiometer-implementation-of-the-tenhl-test/