Aided cortical testing - considerations for unilateral and asymmetrical hearing losses

This video will explore some of the considerations and tactics for performing the aided cortical test on patients with unilateral and asymmetrical hearing losses.

You can read the full transcript below.

Bilateral hearing loss

When performing the aided cortical test on a patient with a bilateral hearing loss, fitted with hearing aids on both ears, the test is relatively straightforward.

This sound field assessment provides information as to how well the patient is able to access speech sounds when using both of their hearing aids together, as they would in the real world.

Asymmetrical or unilateral loss

However, when considering those patients with an asymmetrical or unilateral loss, matters become slightly more complicated and require some additional considerations.

How you approach the test for this patient group will depend on the configuration of their hearing loss and how they are aided.

Dead ear on one side and aidable loss on the other

If the patient has a dead ear, or almost no usable hearing on one ear and therefore hasn't been fitted with a device on that side, but has an aidable loss on the other ear which has been fitted with a hearing aid, then it is simple enough to perform the aided cortical test in the same way as you would for a patient with two hearing aids.

No adjustments are required.

In this instance, you would perform the test in the aided right or left condition depending on which ear has the device fitted and simply make it clear in the notes or comments as to the status of the opposite ear.

Dead ear on one side and normal hearing on the other

If the patient has normal hearing in the unaided ear, then it is important to consider if there is value to be obtained from performing the aided cortical test.

This is where we should remember what the clinical question is, and which answers we are seeking from potentially performing this test.

If, as is the case for most young infants and children, the clinical question is about whether the child is able to access speech sounds in the real world, then we can be confident that their normally hearing ear will support this.

The provision of a hearing aid in the other ear in such a scenario is typically designed to provide localization cues and help in managing background noise.

It is important to have realistic expectations regarding the efficacy of a unilaterally fitted hearing aid.

Depending on the extent of the loss, this device may not be supplying the majority of speech and language information that the child will access.

As a result, many clinicians opt not to perform aided cortical testing on these cases as the usefulness of the information obtained may be minimal.

Bilateral asymmetrical loss

If the patient has a bilateral hearing loss, but this is asymmetrical, then we need to consider the extent of the loss.

If the better ear has not been aided, perhaps because the hearing loss is very mild, then performing the aided cortical test in their real-world scenario, with the hearing aid in situ on the poorer ear, can help to confirm whether the patient is accessing speech sounds as they would be hearing on a day-to-day basis in the real world.

If the results are not satisfactory, then this may point towards aiding the better ear.

If there is a need to perform the aided cortical test in order to assess the aided benefit provided by one single device at a time, then there are some different options as to how to do this.

Essentially, the goal is to remove the opposite device or ear from being able to detect the stimuli delivered and from contributing to the response generated.

One option is to occlude the non-test ear through the use of a foam earplug or their own earmold using something to block the sound hole.

Another possibility is to simply remove the patient's better ear hearing aid from their ear for the duration of the test.

However, this increases the risk that sound may be detected by this ear, depending on the extent of the loss.

Using additional ear defenders over the non-test ear, whether it has been occluded or not, can help reduce the likelihood of the stimuli being detected.

Another option, which many clinicians have queried, is the possibility of using a separate audiometer with which to deliver masking noise via a transducer to the non-test ear.

However, there are a number of practicalities which make this challenging.

Firstly, the patient groups who typically undergo aided cortical testing may not tolerate an additional transducer with an additional amount of noise being presented.

Secondly, traditional narrowband masking noise is unlikely to be broad enough to cover the frequency range of the speech stimuli being presented.

White noise or speech noise are more likely to have a sufficient bandwidth.

However, it is important to ensure these have been calibrated on the audiometer used and to understand how they may have been calibrated and any associated offset values.

Thirdly, there are no current guidelines or recommendations as to how to calculate the level of masking noise required to effectively mask a speech stimulus delivered via the sound field.

There are risks to using the incorrect level of masking noise.

Not enough masking noise may not effectively prevent the non-test ear from being able to detect the stimulus and contribute to the generation of a response.

Too much masking noise may lead to cross-hearing, whereby the device on the test ear is able to detect the masking noise, and this can lead to the stimulus being masked by the test ear as well and may prevent a response from being generated.

As a result, until such guidelines are developed, it is currently recommended to not use masking noise during the aided cortical test.