Threshold Equalizing Noise (TEN) Test

Table of contents

• What is the TEN test?
• What is a cochlear dead region?
• When to perform the TEN test?
• TEN test procedure
• What to do in case of a dead region

What is the Threshold Equalizing Noise (TEN) test?

Developed by Brian Moore, the Threshold Equalizing Noise (TEN) test is a quick and effective method for detecting off-frequency listening in the cochlea, which may indicate the presence of cochlear dead regions. The test works by measuring pure tone thresholds in the presence of a specially designed masking noise known as TEN.

It is important not to confuse this method with traditional audiometric masking. In the TEN test, both the masking noise and the pure tone are presented to the same ear to detect off-frequency listening, whereas in conventional audiometric masking, narrowband noise is applied to the non-test ear to prevent cross hearing.

What is a cochlear dead region?

A cochlear dead region is an area of the cochlea where there are no functioning inner hair cells and/or auditory neurons (Moore, 2001). When a pure-tone signal is presented to such a region, it may still be perceived if the level is high enough, due to stimulation of adjacent, functioning regions.

This occurs because the pure tone generates sufficient basilar membrane vibration that these neighboring areas of the cochlea, where sufficient inner hair cells and neurons remain, are stimulated. This phenomenon is known as off-frequency listening.

In patients exhibiting off-frequency listening, the threshold recorded on a traditional pure-tone audiogram may not reflect the true threshold of the test frequency presented to the ear. Instead, it may represent the response of adjacent, healthier regions.

As a result, conventional pure tone audiometry cannot reliably determine absolute thresholds in the these patients. In such cases, the TEN test confirms that off-frequency listening is present, and that the threshold recorded on the audiogram is likely due to a cochlear dead region.

When to perform the TEN test?

The presence of cochlear dead regions tends to increase with the severity of hearing loss as measured by pure tone audiometry. Another indicator is the presence of distortion when listening to speech. Moore (2010) recommends considering the TEN test when any of the following audiometric characteristics are observed:

• >90 dB hearing loss at high frequencies.
• 75 to 80 dB hearing loss at low frequencies.
• Steeply sloping hearing loss of 50 dB per octave.
• >50 dB hearing loss at low frequencies, with less hearing loss at high frequencies.
• 40 to 50 dB hearing loss at low frequencies, with near-normal hearing at the medium and high frequencies.

TEN test procedure

Below, we’ll cover the TEN test procedure step-by-step.

1. Pure tone audiometry

The first step in performing a TEN test is to measure an audiogram using traditional pure tone audiometry. If you suspect a dead region, follow up with the TEN test.

2. Set up your audiometer

Set up your audiometer to perform the test (see Table 1 for available options from Interacoustics). The TEN test is performed ipsilaterally, meaning that the tone and the noise are presented in the same ear. You can only conduct it with TDH39, DD45, and insert earphones.

Table 1: Audiometers from Interacoustics that can perform the TEN test.

The test is set to start with the stimulus for channels 1 and 2 directed to the same ear. The tone is presented in channel 1 and TEN is presented in channel 2, with the stimulus in channel 2 reversed (Rev) to have a continuous masking signal during the masking stage of the test.

3. Select the level of the TEN

You can do this using the rules below (Moore, 2009):

Table 2: Selecting the level of the TEN.

4. Threshold search for suspected dead regions

For frequencies with suspected dead regions, conduct a threshold search using the traditional method for air conduction without TEN noise present using a 2-dB step size instead of the traditional 5 dB.

5. Apply the TEN noise

Next, apply the TEN noise to the test ear and reestablish the tonal threshold in the presence of this noise.

6. Diagnosis

Determine if off-frequency listening (and thus a dead region) is present. According to Moore (2009), a dead region at a particular frequency is indicated when the masked threshold is at least 10 dB above both the level of the TEN noise and the non-masked (pure tone) threshold.

It is important to note that failing to meet one or both criteria does not necessarily imply the absence of a dead region, it simply means that a dead region has not been detected by the TEN test.

The example below shows an example of a positive TEN test, with masked thresholds indicating dead regions (Figure 1).

For example, when looking at Figure 1, we can see a threshold of 80 dB HL at 750 kHz when measured in the presence of TEN. The non-masked threshold at this frequency is 55 dB HL. Going back to Moore’s (2009) rules, the TEN level at 750 kHz was 70 dB HL, indicating a dead region as being present because:

• The masked threshold of 80 dB HL is 25 dB HL above the non-masked threshold of 55 dB HL.
• The masked threshold of 80 dB HL is 10 dB HL above the level of the TEN noise.

What do I do if I record off-frequency listening and suspect a dead region?

Dead regions can significantly affect speech perception and reduce the benefit of hearing aids, especially when they are extensive. In such cases, avoid amplification at the affected frequencies, and adjust hearing aid settings to target adjacent, functioning regions.

Published literature suggests applying amplification at 1.7x the edge frequency for high-frequency dead regions (Moore, 2001) and 0.56x the edge frequency for low-frequency dead regions (Vinay et al., 2008).

Techniques such as frequency lowering or transposition may be helpful, particularly for high-frequency dead regions, but more research is needed. It is important to counsel patients about the implications of off-frequency listening and how it may impact their listening experience.

While dead regions are more commonly found in the high frequencies, they can also occur in the low frequencies. In summary, identifying dead regions can support clinical decision-making in several ways:

• It informs the selection of appropriate hearing aid technology.
• It helps counsel patients and manage expectations on hearing aid benefit.
• It can guide cochlear implant candidacy decisions, especially when dead regions are extensive, and may also assist in determining optimal electrode insertion depth.

References

Moore B. C. (2001). Dead regions in the cochlea: diagnosis, perceptual consequences, and implications for the fitting of hearing aids. Trends in amplification, 5(1), 1–34.

Moore, B. C. J. (2010). Testing for cochlear dead regions: Audiometer implementation of the TEN(HL) test. The Hearing Review.

Vinay, Baer, T., & Moore, B. C. (2008). Speech recognition in noise as a function of highpass-filter cutoff frequency for people with and without low-frequency cochlear dead regions. The Journal of the Acoustical Society of America, 123(2), 606–609.