Aided Cortical Testing: A Complete Guide

The aided cortical test can be likened to an evoked potentials method for performing a speech test. This guide will provide a complete introduction to aided cortical testing.

Table of contents

• What is aided cortical testing?
• Why should we do aided cortical testing?
• Who should we do aided cortical testing on?
• Which stimuli should be used for aided cortical testing?
• How to set up the equipment for the test
• How to use the Sound Field Analyzer
• Patient preparation
• Interpreting aided cortical waveforms

What is aided cortical testing?

To understand what aided cortical testing involves, it's helpful to firstly take a step back and consider what traditional cortical testing is and involves.

Categorizing auditory evoked potentials

When considering auditory evoked potentials, these can be categorized in several different ways.

We can consider the latency or timing of the evoked potential response and differentiate between different responses accordingly. Short latency responses include cochlear microphonics, electrocochleography, and the auditory brainstem response. The middle latency response occurs at a longer latency, and then we have the very longest of our evoked potential responses.

We can also consider or categorize evoked potential responses according to anatomical region.

The earliest of our responses are generated by the cochlea, auditory nerve, and the auditory brainstem. As we progress further along the auditory pathway, the longer latency responses such as the middle latency response is generated at the thalamus, and those longest of responses are generated by the cortical region, the furthest part of the pathway.

Cortical responses are typically seen as the P1-N1-P2 complex, which appears at around 100 to 300 milliseconds. There are a number of different names used for these tests, and many of these are interchangeable. Some of these tests are standard threshold or detection assessments, but we also have mismatch negativity (MMN) and P300 which look more at discrimination ability.

A standard threshold cortical assessment involves presenting tonal frequency-specific stimuli via insert earphones in order to establish threshold information with the goal of acquiring an audiogram. This is often preferable to ABR assessment as the patient must be awake rather than asleep, which is easier to achieve in adults and older children. Further advantage of cortical assessment over ABR is that it provides information regarding the full extent of the audiological pathway, beyond just the brainstem.

It is also now possible to perform aided cortical assessment, which involves presenting the stimuli via a loudspeaker instead of the insert earphone transducers.  Whilst facing the loudspeaker, the patient has their hearing device or devices in-situ and switched on.

Because this is an aided test, speech sounds are used as the stimuli instead of tonal sounds. This is important because hearing aids are designed to listen to speech sounds. There can be variability in how hearing aids process tonal sounds. Standing waves can also become problematic in a free-field setting.

Ultimately, the goal of any form of aided testing is to know whether the patient is able to hear speech sounds properly with their device or devices in situ.

Aided cortical responses in adults

With aided cortical testing, or indeed any cortical testing, the waveform morphology in adults is generally quite clearly defined and repeatable and consistent across patients. In Figures 1-3, we can see a number of different waveforms, showing that traditional P1-N1-P2 complex.

Aided cortical responses in children

In children, it's a different matter. As you can see from the waveforms below (Figures 4-6), there is a much less clearly defined response morphology, and the literature shows that there is large variability in the response morphology between subjects. This is largely due to the immature cortex in this age group. The cortex does not fully mature until teenage years.

Aided cortical responses in cochlear-implant patients

When testing patients with cochlear implants, a similar morphology can be seen, such as that shown in Figure 7 below.

However, sometimes it can be possible to record an artifact when testing patients with cochlear implants, so care must be taken when interpreting such responses. We can see artifacts in this set of recordings (Figure 8).

These artifacts can look quite similar to cortical responses. Key warning signs that an artifact is present is the slightly triangular or square shape present in the waveform. We can see the first positive inflection appears much earlier in latency than we would expect for a cortical response. Here it is just after 0 milliseconds. It is also likely to appear very quickly from the start of the recording.

It is possible to examine any suspected artifacts by removing the display filter settings. When an artifact is present within the waveform, the peak of the artifact is likely to become flat and square-shaped upon removal of the display filter settings. A true cortical response would not modify in this way: When removing the high-pass filter setting, in particular for a non-artifactual response, there is likely to be little change to the shape of the positive inflections.

When testing patients with cochlear implants, it is important to explore these elements of the waveform to help distinguish between genuine responses and artifacts. Clinicians assessing patients with cochlear implants should proceed with caution when interpreting waveforms as the objective response detector may indicate the presence of a response when in fact the waveform contains an artifactual morphology.

Why should we do aided cortical testing?

So why should we be performing aided cortical testing? What benefit can it bring to the audiological test battery?

When it comes to fitting a hearing aid, there are many steps involved to ensure that the device is well-programmed. This includes performing accurate audiometry, speech testing, maybe speech-in-noise testing as well. Clinicians might perform audible contrast threshold (ACT™) testing. An appropriate device is selected for the patient, their audiogram and their needs. HIT box measurements are useful to help ensure the hearing aid is working properly. And the device should be verified using real ear measurements or RECD measurements.

But how do we know for sure if the device is actually doing its job properly? This is a question that differs for different people and different age groups.

For an older adult, it might be a matter of, does the device allow them to hear the television properly or to hear their grandchildren properly in the playground?

For someone in the workplace, it might be about whether the hearing device is working such that they can listen clearly in meetings or to presentations.

For children, it might be about whether they are able to hear the teacher in the classroom.

And for young infants, it's almost always about whether they can hear well enough to learn and develop their own speech and language.

This is why early intervention is so important. The child will only learn to speak as well as they can hear. So if they don't hear certain sounds, they will struggle to learn to speak themselves.

Outcome measures

To find out if a device is working as desired for that individual, it is possible to use what are called outcome measures. These are methods of measuring how good an outcome the patient is deriving from their device.

The clinician can ask the patient, using self-reporting measures, and get them to provide feedback about their personal experience of using the device in those situations where they need it to work well for them.

Validated questionnaires are also an option, and these exist for different age groups, crossing adults and children.

The input of other people in the patient’s life can also be valuable. For children, this might be their schoolteachers, asking how their school progress is going - are they keeping up with the rest of the class?

It is also possible to do direct speech testing with the patient, and speech-in-noise testing as well, with the hearing aids on to answer the question of: Does the patient hear more speech sounds with their devices on than they did without the devices?

But what if the patient can't do any of these outcome measures?

Maybe they're too young to self-report. Maybe they have additional disabilities or complex needs, such as a developmental delay or cognitive difficulties. Maybe they're too young for their parents or teachers to have any reliable reporting about their progress. This is where aided cortical testing becomes really valuable.

The aided cortical can be likened to an evoked potentials method for performing a speech test. If a cortical response is present to the speech sound delivered to the patient, then there is confidence that they can hear it. This can be done with or without their hearing devices in situ. It is then possible to make that comparison between aided and unaided performance.

Gap in infant hearing assessment

At the neonatal stage, the available audiological tests are limited to those which require no cooperation from the patient:

• ABR
• OAEs
• ASSR testing
• Tympanometry

These tests can easily be performed under natural sleep, however after approximately three months of age it becomes much more challenging to maintain sufficient natural sleep for the testing required.

Once a child has developed the trunk and neck control to be able to sit upright and perform a head turn, visual reinforcement audiometry (VRA) becomes possible. This typically occurs at around 7-9 months of age. VRA involves the child turning in response to a stimulus, upon which they are then rewarded with a visual reinforcer such as a toy or a video on the screen.

And it is at around two and a half to three years of age when a child can progress to a more cooperative task, such as play audiometry, where they perform a more conscious task in response to the heard stimulus.

Therefore, there is a gap between the ages of three to seven months where very limited testing options are available. ABR testing can be performed under sedation, however this carries risks and comes with more complicated practical consideration.

Frequently at this age, for those children who have been issued with hearing aids, the main clinical question is not about their underlying hearing levels, but rather whether and how well their hearing instruments are working for them. As a result, ABR testing is not suitable to answer this question.

Newborn hearing screening programs

At the neonatal stage, newborn hearing screening programs have been implemented in order to provide early intervention for children with hearing loss, and it is well known that early intervention leads to better outcomes for our patients. In many countries such as the US, England and Australia, newborn hearing screening programs work to a target of offering a screening test to 97% of babies within the first month of life.

Following newborn screening, the next step in the clinical pathway is to perform a diagnostic assessment of the child's hearing.

In England, there is a target that 97% of babies should be seen for diagnostics within four weeks of referring on their newborn screening test. The statistics for 2020-21 showed that this outcome was under target but largely influenced by the coronavirus pandemic.

In the US in 2021, 36.646 patients were seen for diagnostics following the newborn screen, and 4.252 were diagnosed with a permanent hearing loss by three months of age.

In Australia, there's a target that greater than 97% of children referred from the newborn screen should undergo diagnostic audiology assessment by three months of age.

Early intervention does not stop at the point of diagnostics. To ensure the best outcome, it is essential that amplification is provided where warranted, as soon as possible.

In Australia, hearing aid fitting should take place as early as possible, but no later than six months, with a target of over 85 % of children with bilateral permanent childhood hearing impairment to be fitted by six months of age.

In England, hearing aid fitting should be offered within four weeks of confirmation of a permanent childhood hearing impairment.

In the US, the target is to enroll patients in an early intervention program within six months of age. In 2021, this led to 2,750 babies being enrolled, many of whom will have received hearing aids, but this also includes those referred for family support, cochlear implants or medical intervention.

It is clear to see how newborn hearing screening has brought forward not only the diagnosis of hearing loss, but also the fitting of hearing aids to a much earlier point in time. Prior to these screening programs being in place, many hearing losses simply would not have been identified until much later in life when parental concerns or difficulties with speech and language development became apparent.

Aided VRA

At the age of 7 months and over, VRA is typically the behavioral test of choice. It can be used to perform standard audiometry, where frequency-specific hearing thresholds are recorded. However, as a test method, it also has other applications.

VRA can be used to perform speech testing, whereby instead of traditional tones, the child's ability to detect speech sounds is assessed. As this is a test that can be performed via free-field speakers, it is possible to perform VRA with the child's hearing devices in situ in order to assess their aided benefit.

By comparing the results of VRA speech testing with the child wearing their hearing aids to the results of the same test without the hearing aids, it's possible to measure whether the devices are providing clear benefit to the child.

Challenges of aided VRA

Assessing aided benefit via VRA is not without its challenges.

Frequently, at the age at which VRA becomes first possible, the main clinical focus is on repeating unaided audiometry. A period of around six months or longer could have passed since the child's hearing thresholds were initially measured via ABR or ASSR, and so re-establishing thresholds is often prioritized over aided testing in order to confirm whether the hearing levels have remained stable and to assess additional frequencies that may have been tested at that neonatal stage.

This can be further compounded if the patient presents with middle ear effusion, a common presentation in young children, which increases the likelihood of changes to the hearing levels.

Establishing the extent of any fluctuations is important, particularly for a hearing aid wearer who may need adjustments to their amplification settings as a result. If changes to the child's hearing thresholds are noted, whether this is linked to the presence of middle ear dysfunction or not, the importance of establishing whether the underlying sensorineural loss has changed as well, or not, is often deemed the next most important priority.

As a result, performing aided testing is often deemed a much lower priority, and so it can be several assessments, several months later before that opportunity to perform aided testing via VRA arises, particularly if those fluctuations and changes in hearing levels continue over time. This can lead to an even bigger gap between the point of diagnosis or the fitting of those hearing aids and the point at which aided behavioral testing becomes realistically possible.

The end result is that there is a significantly long duration of time for not only clinicians but also for the parents of the child to not have that information or that confirmation as to whether the hearing devices are indeed working effectively.

Establishing aided benefit, or indeed the lack of aided benefit, at an earlier point in time can allow clinicians to adjust the hearing aid in order to provide the best amplification and ensure the best outcomes during what is a highly critical time period in terms of neuroplasticity and speech and language acquisition.

Who should we do aided cortical testing on?

Let’s cover the different target populations below.

Infants aged 3 to 7 months

One of the main groups that can benefit from aided cortical testing is infants and young children. In particular, infants aged 3 to 7 months in order to confirm that their hearing aid fitting has been successful. This group may have been diagnosed following the newborn hearing screening process and had either an ABR or ASSR to identify their hearing thresholds and then move on to the hearing aid fitting process.

However, at this age, they're still too young for behavioral testing such as visual reinforcement audiometry. Furthermore, even when they get to that point of age, it can be some time before aided behavioral testing is done, if at all, because the priority tends to be repeating the hearing test without the hearing aids in.

For this age group, it is really important that we know if their hearing aids are working as intended. It is such a critical speech and language period for these young infants that it's important that we know if the aids are doing the job properly and if not so that we can adjust as necessary.

Young children that cannot do behavioral testing

The aided cortical test is also suitable for any young child who, for whatever reason, cannot or is not doing behavioral testing. It may be that there is some kind of developmental delay, they could have some disabilities or complex needs, or they may simply not be very reliable at the behavioral test being asked of them.

The aided cortical test provides an easy way to see whether the hearing aids are providing the sounds that the patient needs in order to develop their speech and language.

Children with ANSD

Another group of children who are of particular interest for the aided cortical test are those who've been identified as having auditory neuropathy spectrum disorder (ANSD). These children, again in that 3 to 7+ month age spectrum, may have had their ABR and the ANSD identified at that process but aren't yet ready to perform behavioral testing.

It is known that it is not possible to obtain reliable hearing levels from the ABR results in cases of ANSD and this often results in these children not having hearing aids fitted until behavioral testing is undertaken. There can be fluctuations and variability in the reliability of testing for these children, so often they are not fitted with hearing aids until they are much older.

It is possible to use the aided cortical test in the unaided condition, and the evidence shows that if responses are seen to soft sounds on the aided cortical test, there's likely no worse than a mild hearing loss present in these cases with ANSD (Pearce et al., 2007).

This information can therefore be used to inform whether hearing aid fitting is appropriate and at what levels might be suitable for programming of the hearing aids. Previously, this would have had to wait for behavioral testing, which is often unreliable in this group.

Therefore, earlier intervention is possible with this group of patients in order to support their speech and language development. Often, these children end up being referred for cochlear implantation, so the results of aided cortical testing can inform that process as well.

Infants and young children with a severe to profound hearing loss

Within the infant and young children group, it's important to also highlight those who've been diagnosed with a severe to profound hearing loss. This is a very important group who often end up being referred for consideration of cochlear implantation, but for this they must try hearing aids first.

This group can often be very difficult to condition for behavioral testing because of the raised hearing thresholds present. Aided cortical testing can be used to show whether there's any benefit being derived from the hearing aids, which can then feed into the cochlear-implant-decision-making process.

Cochlear implant users

The aided cortical test can also be used for cochlear implant users. Most of these patients will perform some form of aided testing with their implants in situ, but if this isn't possible for whatever reason, aided cortical testing is an option.

There are some limitations around the likelihood of artifact being present in the aided cortical response, which can contaminate the response. So it's important that clinicians proceed with caution and an awareness of what this artifact might look like and how to be mindful of when it might be present.

Older children that cannot do behavioral testing

Another group of patients who may be suitable for aided cortical testing are older children. Any child who is not performing reliable behavioral testing, for whatever reason, may be suitable for aided cortical testing. This may be due to a genuine difficulty in performing the behavioral test due to some complex needs, developmental delay, disabilities.

Older children with non-organic hearing losses

There is also another group of patients in this older-children group that it is important to be aware of, which are those who present with non-organic hearing losses.

A non-organic hearing loss is where there's a hearing loss presented on the audiogram, and often this is a very reliable hearing loss, but there is an indication in the results or in how the patient is behaving to suggest that the pure tone audiogram thresholds aren't true results.

Sometimes, this group are known as malingerers. They may have normal hearing and be presenting with an untrue hearing loss. They may have a hearing loss which they are then exaggerating. This may be a presentation seen when there are other personal problems in the patient’s life, either at home or at school.

Often, the pure tone audiogram presents with a hearing loss but there might be present otoacoustic emissions, normal speech testing, or the patient’s ability to manage normal conversation in the clinic with the audiologist doesn't match up with the audiometric thresholds.

Adults that cannot do behavioral testing

Adults can also benefit from the aided cortical test. For any patient with complex needs who isn't or cannot perform traditional behavioral testing, the aided cortical test can be a valuable tool in the audiological test battery to help understand some more information about how the patient is managing with or without their hearing aids.

Adult cochlear implant candidates

The aided cortical test can be a valuable test for adult cochlear implant candidates. As is the case for infants, a trial of hearing aids is required before moving on through the cochlear implant candidacy process. Part of that process involves assessing whether the patient is deriving benefit from their hearing aids. The aided cortical test can help provide that alternative information or even simply a cross-check for any behavioral testing that may have been obtained.

Just as in the younger children group, CI users can partake in aided cortical testing with those same limitations around the potential of artifact to be present in the response and the need to proceed with caution when interpreting the waveforms.

When not to do aided cortical testing

Sometimes there may be other tests that are more suitable, such as the ABR, ASSR or threshold cortical depending on what the clinical question is.

Whether one is attempting to establish threshold frequency-specific information or looking for an alternative to speech testing, that will help you to decide which type of test would be most suitable in any given scenario.

Which stimuli should be used for aided cortical testing?

An important consideration when it comes to performing aided cortical testing is around the stimuli used for the test.

The Aided Cortical module on the Interacoustics Eclipse contains a new set of stimuli, which were developed by the University of Manchester and the Interacoustics Research Unit. These are highly frequency specific, with no overlap between them.

They have also been calibrated with reference to the ISTS signal, meaning that each stimulus is presented at the level that corresponds to its frequency band within the ISTS, which is how natural speech works, with the higher frequencies presented at a quieter level than the lower frequencies (Figure 9).

These stimuli were not developed from natural speech, but rather were created synthetically. This allows for the excellent frequency specificity of these stimuli. Such a narrow frequency specificity cannot be obtained from natural speech tokens which stimulate a much wider frequency spectrum and run the risk of measuring cortical responses to stimulation of areas of the basilar membrane that don't correspond with the peak frequency region of the stimulus.

The method of calibration for these stimuli aligns them with the ISTS, which means we are presenting sounds to the patient as they would hear them in the real world. This means we are performing an accurate assessment which is representative of how the patient hears speech via their hearing devices.

There are other stimuli available within the aided cortical module. For a deep dive into the differences between these stimuli, please read more here: Which stimuli should be used for aided cortical testing?

’Ladies in the Van study’

The following video is an interview with Dr. Anisa Visram, the lead author of the well-known ‘Ladies in the Van’ study which used the ManU-IRU stimuli with the Eclipse device to perform cortical testing on a group of infant hearing aid users (Visram et al., 2023).

How to set up the equipment for the test

This following video demonstrates how to set up the equipment for the Eclipse Aided Cortical module. You can read the full transcript below.

Transcript

When doing aided cortical testing, it is important that testing is done in a proper environment. Factors such as ventilation and computer fans can mask the noise presented from the free field speaker. It is recommended to perform the test in a quiet environment.

The aided cortical test is primarily performed on infants, small children, and patients with complex needs. The patient should be awake and engaged during testing. Use quiet toys, interesting objects, or silent videos to keep your patient engaged while the test is running. Any screens used should be placed above the free field speaker to ensure the patient is facing toward the source of the stimuli.

Place the patient where the initial calibration was performed, which should be 1.5 m away from the free field speaker. The patient should stay in the same place during testing. When testing infants, either seat them in an appropriate chair or on the lap of their adult. If the position of the patient is changed, the sound field analysis should be repeated to compensate for the change in test environment.

How to use the Sound Field Analyzer

This following video demonstrates how to use the Sound Field Analyzer in the Eclipse Aided Cortical module. You can read the full transcript below.

Transcript

Changes in the test room can affect the stimulus intensity of the aided cortical test. The sound field analyzer compensates for this, ensuring the patient always receives the correct stimulus intensity. We recommend running the sound field analyzer before each aided cortical test you perform.

To use the sound field analyzer, first open the Aided Cortical module. Place the ambient microphone where the patient will sit. The microphone should be level with the patient's ear. Click ‘Sound field analysis’ in the menu on the left. Press ‘Analyze sound field’ in the software.

The speaker will now play a pink noise signal, and the software will measure the intensity of each stimulus compared to the calibrated target. Let the noise signal run for a few seconds, then press ‘Analyze sound field’ again to stop the noise presentation.

If results do not match the calibrated target as seen here, you can press ‘adjust to target’. This will adjust the stimuli to match the calibrated levels. Press ‘OK’ to save your sound field analysis. The adjusted value is also shown on the report.

If you want to use a saved sound field analysis, click the dropdown menu and choose the saved sound field analysis. Adjust to that target and press okay to save. This feature is useful when the equipment is frequently moved between different locations.

Patient preparation

When undertaking an aided cortical assessment, it's important to perform the appropriate patient preparation steps and to ensure the patient is in the optimum state throughout testing.

There are a number of steps to follow to prepare the patient for testing, which will help to maintain the appropriate patient state and support the recording of accurate results for the aided cortical test.

1. Skin preparation and electrode placement

When undertaking skin preparation and electrode placement, the process is identical to ABR, ASSR or threshold cortical assessment. Use electrode gel and some gauze or cotton wool to clean the skin.

As the electrode is a two-channel system, four electrodes will be required for testing. There are many different types available, however it's important to consider the size of these electrodes, particularly if testing on young infants.

The vertex electrode is placed on the high forehead or true CZ. The ground electrode can go on the low forehead or the cheek, and the two reference electrodes should be placed on the mastoid prominence behind each ear.

Aim for all electrode impedances to be below 5 kiloohms. They should also be balanced across the four electrodes with no more than a 1 kiloohm difference between each electrode.

2. Check the hearing aids

If performing the test in the aided condition, it is vital to check the hearing aids before testing. If the patient, parents or carers report any problems or issues with the devices, it is important to troubleshoot this before running the aided cortical test. Use a hearing instrument test box measurement to check for any faults or problems.

Ear molds, domes or other earpieces should be checked for appropriateness of fit, blockages, or any necessary repairs. When testing infants, new ear molds are needed very regularly, so it can be worth trying to arrange for new impressions to be made ahead of the aided cortical appointment to ensure a good fit on the day of testing.

Also, consider when the hearing aids were last verified. RECDs should be performed regularly for infants, so consider performing an up-to-date verification measurement with the patient's most recent ear molds to ensure the best delivery of sound to the ear.

Lastly, something that may appear to be obvious but can easily be overlooked, is that it is crucial to ensure the devices are switched on, fitted in the ears correctly, and have either new batteries in place or a full charge before starting the aided cortical test.

3. Instruct the parents, carers or the patient

When testing a young child, it's important to give the parents or carers some instructions so that they understand how to help during the test. Discuss with the parent where the child would be seated best. On their own? Using a highchair? Using a small children's chair? Or on the parent's lap?

It's important to explain the nature of the test to the parents or the patient themselves in the case of an older child or adult. They should have realistic expectations as to the likely length of the test, as well as an understanding of what the patient needs to do during the test and what the goal or intention of the test is.

4. Maintain the optimum patient state

Maintaining the optimum patient state is crucial for a successful aided cortical test. Let’s cover ways to do this below.

Engagement toys

For young children and infants, a wide range of engagement toys is absolutely essential. The very youngest of infants require regular changes of toys. The goal is to keep the child seated calmly for the duration of the test without falling asleep or growing too excitable or agitated.

Cartoons or videos

Favorite cartoons or videos on a smartphone or tablet device can be useful. Some clinics have acquired projectors in order to create a cinematic effect within the clinic room whereby they project sensory or children's cartoons onto a wall or projector screen.

Age-appropriate engagement

Any form of engagement should be age-appropriate. For older children or adults this could be reading a book or watching a silent film or TV show with the subtitles on to keep them interested.

Second tester

It is recommended to have a second tester to play and engage with infants and young children so that the first tester can concentrate on the testing process.

Adapt to the situation

Be prepared that what works for a period of time may stop being as successful so you may need to change the engagement activity regularly and frequently.

As the patient has electrodes and cables attached to them, we want to keep their hands busy to stop them pulling on the cables and detaching the electrodes. Remember it is okay to pause the test midway through if the child grows too active or upset.

Monitor the patient’s EEG

In the Eclipse software, it is possible to see the individual patient's EEG and use this to guide the engagement activity. When the EEG lines turn red, this means the sweeps are being rejected. So if there is consistent red, it can be worth pausing the test and trying to alter the engagement activity or have a break for a cuddle or some snacks and reset before continuing on with testing.

Video example

The following video demonstrates the aided cortical test in action on a 6-month-old infant hearing aid wearer.

Interpreting aided cortical waveforms

It is well documented in the literature that infant cortical morphology is highly variable between subjects, as referenced by the BSA Recommended Procedure for Cortical Auditory Evoked Potential Testing (2022). This can make it challenging to accurately detect the presence of a response with confidence.

The BSA Recommended Procedure highlights the value of using objective response detection algorithms for the interpretation of such waveforms. Carter et al. (2010) explored the clinical utility of automatic response detection and found that there was a likely increase in clinicians’ confidence when reviewing cortical responses.

In auditory evoked potentials, detection algorithms have been well established for some time. Fsp evolved into Fmp (which are both well established in ABR testing), and the latest evolution to these algorithms is called Fmpi™.

Fsp and Fmp essentially calculate a signal-to-noise ratio based on the statistical variance of the measured average overall waveform in relation to the estimated residual noise of the waveform. Fsp estimated the residual noise based on just one single point of data on the waveform.

Fmp extended this to making use of multiple points of data on the waveform (5 to be precise). Fmpi also calculates a signal-to-noise ratio, but now all of the measured data points on the waveform are included in the calculation. In the case of an aided cortical measurement, this comes to 250 data points.

Furthermore, the individual listener’s brain activity (EEG) is taken into consideration with Fmpi, which doesn’t happen in Fsp or Fmp where a conservative estimation of the EEG is used. The end result is that, with Fmpi, the detection of a cortical response can be established with fewer numbers of sweeps, and thus less time, than Fsp or Fmpi in the majority of patients.

The default setting with the Eclipse Aided Cortical module is for Fmpi response detection to be set at 95%. However, 99% can also be selected should you prefer. In Figure 10, we can see a response confidence Fmpi value of over 99% has been achieved within 66 sweeps.

Related course

On February 13, 2025, Amanda Goodhew will host an eWorkshop on aided cortical testing. This eWorkshop will explore advanced topics relating to aided cortical testing, with a particular focus on the pediatric application of the test. This course will consider how to use the objective tools available to aid interpretation of aided cortical waveforms.

Case studies will be used to demonstrate how to formulate the most suitable testing strategy for each individual patient. Complex testing scenarios, such as cochlear implant patients, will be discussed with suggestions for alterations to test technique and strategy to support obtaining accurate results.

Learning objectives:

• Explain how to interpret aided cortical waveforms
• Determine an appropriate testing strategy for aided cortical testing based on the patient’s expected audibility
• Describe the options available for managing complex aided cortical testing

When? February 13, 10.00-11.30 / 16.00-17.30 CET (identical sessions to cater for time zone differences).

• Register for session 1
• Register for session 2

References

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Visram AS, Stone MA, Purdy SC, Bell SL, Brooks J, Bruce IA, Chesnaye MA, Dillon H, Harte JM, Hudson CL, Laugesen S, Morgan RE, O'Driscoll M, Roberts SA, Roughley AJ, Simpson D, Munro KJ. Aided Cortical Auditory Evoked Potentials in Infants With Frequency-Specific Synthetic Speech Stimuli: Sensitivity, Repeatability, and Feasibility. Ear Hear. 2023 Sep-Oct 01;44(5):1157-1172. doi: 10.1097/AUD.0000000000001352. Epub 2023 Apr 5. PMID: 37019441; PMCID: PMC10426785.

Dillon, H. et al. (2006). Automated detection of cortical auditory evoked potentials. [Abstract] The Australian and New Zealand Journal of Audiology, 28 (Suppl.), 20.

Golding, M. et al. (2006). Obligatory Cortical Auditory Evoked Potentials (CAEPs) in infants — a five year review. National Acoustic Laboratories Research & Development Annual Report 2005/2006. Chatswood, NSW, Australia: Australian Hearing, 15 - 19.

Golding, M. et al (2007). The relationship between obligatory cortical auditory evoked potentials (CAEPs) and functional measures in young infants. Journal American Academy Audiology, 18, 117-125.

Golding, M. et al (2006). The effect of stimulus duration and interstimulus interval on cortical responses in infants. Australian and New Zealand Journal of Audiology, 28, 122-136.

Stone, M. A., Visram, A., Harte, J. M., & Munro, K. J. (2019). A Set of Time-and-Frequency-Localized Short-Duration Speech-Like Stimuli for Assessing Hearing-Aid Performance via Cortical Auditory-Evoked Potentials. Trends in Hearing, 23, 233121651988556.

Dillon, H. (2023a). Phoneme levels for use in evoked cortical response measurement [Internal report].

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Carter L, Golding M, Dillon H, Seymour J. The detection of infant cortical auditory evoked potentials (CAEPs) using statistical and visual detection techniques. J Am Acad Audiol. 2010 May;21(5):347-56. doi: 10.3766/jaaa.21.5.6. PMID: 20569668.

British Society of Audiology (2022) Recommended Procedure Cortical Auditory Evoked  Potential (CAEP) Testing.