The threshold equalizing noise (TEN) test consists of measuring pure tone thresholds with a special masking noise TEN.The TEN test was developed to provide clinicians with a quick and easy way to identify cochlear dead regions.
A dead cochlear region is defined as a region of the cochlea where there are no functioning inner hair cells and/or neurons (Moore, 2001). When a pure-tone signal “falls” into a dead region, it can be heard by neighbouring hair cells, if the intensity of the signal is loud enough. This is because the pure tone produces sufficient basilar-membrane vibrations in neighbouring areas of the cochlea, where there are surviving IHCs and neurons. This phenomenon is defined as “Off Frequency Listening”. Clinically, this will be presented as a threshold on the traditional pure tone audiogram, but it may not be the real threshold. It is not possible to use traditional pure tone audiometry to determine if there is a dead region present; the TEN test was developed for this very purpose.
Characteristics that could indicate the presence of a dead region (Moore, 2009):
The TEN test is performed ipsilaterally, meaning that the tone and the noise are presented in the same ear. It can only be conducted with TDH39, DD45 and Insert earphones.
If operating the audiometer from the PC the TEN noise will be available in channel 2 if licensed. To enable the TEN noise press TEN (a). Ensure it is presented to the same ear as in channel 1 (b). The decibel step size can be changed to 2dB (c).
A dead region at a particular frequency is indicated when a masked threshold is at least 10dB or more above the level of the TEN and the masked threshold is at least 10dB above the non-masked threshold.
The example below shows an example of a positive TEN test, with a masked threshold indicating a dead region.
If dead regions are present, this may have important implications for fitting hearing aids and for predicting the likely benefit of hearing aids. When a patient has a dead region, there may be little or no benefit from hearing aid amplification for frequencies well inside the dead region (Moore, 2009).
Identifying a cochlear dead region can:
Moore, B. C. J. (2001). "Dead regions in the cochlea: Diagnosis, perceptual consequences, and implications for the fitting of hearing aids," Trends Amplif. 5, 1–34.
Moore, B. C. J. (2009). “Audiometer Implementation of the TEN (HL) Test for Diagnosing Cochlear Dead Regions”.