Dead Region - Gives Valuable Information

Evaluation for the dead region is becoming a hot topic in the field of audiology. Have you heard of TEN test ? TEN stands for Threshold-Equalizing-Noise test, and the application of this test is getting more recognized as it is already available in some audiometers such as Affinity2.0 & Equinox2.0 PC-based Interacoustics audiometer. Previously, this test has been conducter via audiometer connected to compact disc player. The main function of this test is to identify the dead region in cochlea.

Wait a minute - What is Dead Region ?

Dead region consists of non-functioning Inner Hair Cells (IHC) or neuron, causing 'holes in hearing' . Well, IHC plays important role in stimulating the auditory nerve and so their loss may lead to abnormally large vibration of basilar membrane. Even so, the vibration can't be detected by the neurons connected to the particular region! So if a high frequency tone presented to the dead high-frequency region, the vibration will not trigger neural response over that region. Anyway, there is chance for 'off-place listening' when the vibration is sufficient enough to stimulate basilar membrane region near apical region (lower frequency region). Then, the high tone is heard as a lower frequency sound.

Note the difference, in Outer Hair Cell (OHC) damage alone, vibration of basilar membrane for a low-level sound will be reduced, anyway the intesity of vibration is restored with louder sound.

TELLSIGN - any hearing loss of above 70 dBHL is often associated with dead region, but of course normal puretone audiogram can't confirm this condition.


Figure shows dead region or 'holes in hearing' in cochlea derived from a young man who was exposed to gunshot before dying.

Source :http//://www.hearingreview.com/issues/articles/2010-01_01.asp


What is the sense in TEN ?

The test involves detecting threshold of a puretone in presence of background noise. For those who are interested, please refer to http//://www.hearingreview.com/issues/articles/2010-01_01.asp

The idea of this test is the signal threshold will be higher than normal in cases with dead region, in presence of noise. The masked threshold will be at least 10 dB above the absolute threshold 10 dB above the nominal noise level.

How will this be helpful for me?

Identifying the dead region could help us in making some important decision, especially when it come to the mode of amplification. For instance, a patient with dead high-frequency region, could possibly benefit from hearing aids with frequency transposition function and does not unnecessarily requires high-frequency (>1700 Hz) amplification which may lead to problems such as distortion and acoustic feeedback.

Patients with dead low-frequency region do not need emphasis on low-frequency amplification (< 0.5 k Hz), as this can further reduce the speech inteligibility.

If your patient is a candidate for Hybrid, TEN test might be helpful in determining the edge frequency of dead region, to assist in deciding the depth of electrode insertion.


In summary, understanding the physiology of hearing loss thoroughly will help us in implementing the most suitable amplification and rehabilitation management for our patients. It also prevent unnecessary hassles to both professional and patients.