Lec 12: Cortical auditory evoked potentials (CAEP)

Introduction to Auditory Evoked Potentials (AEP)

• Definition: Auditory evoked potentials are electrical activities within the auditory system evoked by an auditory stimulus. These neural responses are time-locked to specific auditory events.

• Timeline and Generators:

  • Auditory Brainstem Response (ABR): Occurs very early, within the first $10\,ms$ after stimulus initiation. Generators are located in the brainstem.

  • Cortical Auditory Evoked Potential (CAEP): A much later response occurring as early as $50\,ms$ and extending into the $100\,ms$ to $200\,ms$ range. Generators are located higher up in the central nervous system, specifically in the auditory cortex.

• Complexity: As the signal moves from the auditory nerve up the brainstem to the cortex, the pathway becomes more complex with increased connections, interconnections, and contributing centers. Unlike the "one train line" of the lower brainstem, the auditory cortex involves significant cognitive and interactive components.

• Amplitude: Cortical responses have a much larger amplitude than ABR responses because the neural regions are larger and the electrodes are placed closer to the generators.

Classification of Potentials: Exogenous vs. Endogenous

• Exogenous Potentials:

  • Primarily determined by the physical characteristics of the stimulus.

  • Recorded regardless of the subject's attention (e.g., ABR can be recorded while the patient is asleep).

• Endogenous Potentials:

  • Highly dependent on the stimulus context (e.g., change in stimulus) and the subject’s internal state (e.g., attention, cognition, alertness).

  • If the patient is asleep, habituated, or not focused, the trace may be poor or absent.

Neural Generators and Waveform Components

• Components: The standard cortical waveform consists of three primary peaks/troughs:

  • P1: The first positive peak.

  • N1: The first negative trough (most significant for visual identification).

  • P2: The second positive peak.

• Identification: Clinicians look for presence versus absence and the general shape. Exact millisecond latency shifts are less critical than in ABR, though latency does increase as stimulus intensity approaches the hearing threshold.

Stimulus Parameters for Cortical Testing

• Stimulus Type: Can use clicks, tone bursts, noise bursts, or speech stimuli (e.g., specific syllables or phonemes).

• Rise and Fall Time: Requires a longer rise and fall time than earlier responses, typically between $10\,ms$ and $20\,ms$.

• Intensity: Higher intensity produces larger amplitudes. Latency remains fairly stable at supra-threshold levels but shifts/increases significantly only as we get close to the actual hearing threshold.

• Inter-Stimulus Interval (ISI):

  • The $N1-P1$ amplitude increases as the ISI increases up to about $5\,seconds$, where it begins to plateau.

  • ABR uses fast rates ($11\,Hz$ to $33\,Hz$), but CAEP requires very slow presentation (intervals of several seconds).

• Sweeps: Over-averaging is counterproductive. While ABR may require thousands of sweeps, CAEP typically only requires $20$ to $30$ per average. Exceeding $50$ sweeps often results in a flattened response due to habituation.

• Tonotopic Organization: Lower frequency sounds are processed in cortical regions closer to the scalp surface, often resulting in cleaner traces compared to high frequencies.

Patient Characteristics and Requirements

• State of Alertness: Sleep is the "enemy" of cortical testing. Recordings performed during REM sleep result in significantly smaller or absent traces. Patients must be awake and attending to something (e.g., watching a silent movie with subtitles or reading a book).

• Age and Maturation:

  • Adults: Show clean, large, mature traces.

  • Infants/Children: Traces are often messier and smaller in amplitude because the auditory cortex and associated pathways are not yet fully mature. Latency decreases and amplitude increases as the brain matures.

• Habituation: The brain naturally tunes out boring, repetitive stimuli. This is a protective mechanism but hinders testing. Clinicians mitigate this by keeping runs short ($10$ to $20$ sweeps) and changing the frequency or ear tested unpredictably.

• Refractoriness: A biological process where neuronal excitability decreases because the brain gets "tired."

Clinical Implementation and Electrode Setup

• Montage:

  • Low Center Forehead (Ground): Similar to ABR.

  • Center of the Coronal Line (Vertex/Cz): The active electrode is placed at the top of the head to be near the auditory cortex.

  • Earlobes or Mastoids: Reference electrodes.

• Impedance: Goal is less than $10\,k\Omega$. Most importantly, impedances across all electrodes should be balanced (similar values). Coronal placement requires parting the hair and using exfoliating paste or conductive gel.

• Equipment Scale: CAEP responses are much larger (measured in microvolts) than ABR (measured in sub-microvolts). Setting the wrong scale on the equipment can lead to false diagnoses of profound deafness if the clinician is looking for a tiny ABR trace on a large cortical scale.

Clinical Application: Cortical Evoked Response Audiometry (CERA/SARA)

• Purpose: To objectively estimate hearing thresholds when behavioral testing is unreliable. It typically gets within $5\,dB$ to $15\,dB$ of actual behavioral thresholds.

• Medico-Legal/WorkCover Context: Frequently used in cases regarding noise-induced hearing loss compensation. In these scenarios, a behavioral audiogram may be exaggerated (non-organic hearing loss). Courts require an objective definitive measure.

• Search Technique: Descend in $20\,dB$ steps; once the response is lost, ascend in $10\,dB$ or $5\,dB$ steps.

• Case Study: Jeffrey (54 years old):

  • History: Transport industry worker claiming noise-induced loss. Behavioral results were inconsistent (speech at a $100\%$ at $50\,dB$ but inconsistent PTA; OAEs present $1-4\,kHz$).

  • SARA Results: Showed thresholds at $20\,dB$ to $40\,dB$, proving no worse than a mild to moderate loss, contradicting his behavioral claim of severe loss.

• Case Study: Ronald (Intellectual Disability):

  • Goal: Confirm if current hearing aids were sufficient as communication skills had declined.

  • Challenge: Could only sit still for $15\,minute$ intervals; distracted with AFLW (Carlton team) on an iPad.

  • Result: Corticals at $1\,kHz$ and $4\,kHz$ matched previous hearing levels, confirming that a change in hearing was not the cause of his decline.

Clinical Application: HearLab (Infant Testing)

• HearLab System: Used for objective cortical testing in awake infants, often in the free field (loudspeakers).

• Speech Phonemes: Specifically utilizes "m", "g", "t", and "s" to cover the speech frequency range.

• Statistical Evaluation: The software uses a $p$-value (typically p < 0.05) to objectively determine if a response is present, rather than relying solely on visual inspection.

• Aided Cortical Testing: Evaluates the efficacy of a hearing aid fitting about six weeks post-fitting. If an infant does not show cortical responses to soft speech phonemes ($55\,dB\,SPL$), the clinician increases the hearing aid gain or considers cochlear implant (CI) referral.

• Case Study: Eleanor (5 weeks old): Showed no response to soft "m" phonemes; hearing aid low-frequency gain was increased, and subsequent visit showed improved access to sounds.

• Case Study: Xu (4.5 months old): Diagnosed with profound loss. Aided HearLab showed no response even after gain adjustments, providing objective evidence for cochlear implant referral.

Other Clinical Applications

• Auditory Processing Disorder (APD): Used to track the maturation of the auditory pathway. APD children often show "younger"/immature cortical responses compared to age-matched controls. Maturation (decreased latency, increased amplitude) can be tracked after training programs.

• P300 (Cognitive Potential):

  • Occurs roughly $300\,ms$ post-stimulus.

  • Requires an "oddball" paradigm: a "standard" stimulus and a "deviant" stimulus. The brain's response to the change is measured.

  • Used in research for Alzheimer's, dementia, aphasia, and traumatic brain injury.

• Emerging Research:

  • Hyperacusis: Investigating larger-than-normal amplitudes to loud tones.

  • Tinnitus: Exploring objective pitch matching and identifying sites of generation.

Troubleshooting Guidelines

• No Response: Check if the stimulus is actually playing and verify electrode connections.

• Small Response: The patient might be dozing off or habituating to the stimulus.

• Noisy Trace: The patient may be tense or jaw-clenching. Re-instruct them to relax and check for tangled electrode leads or mobile phone interference.

Questions & Discussion

• Question: What kind of scenario in clinic might you consider corticals?

  • Response: Closely associated with non-organic presentations where behavioral tests fail, and also used extensively in APD clinics.

• Question: Why not use ASSR instead of SARA for adults with disabilities?

  • Response: SARA/CAEP in adults is more reliable and gets closer to actual behavioral thresholds ($5\,dB$ vs. common elevations in ASSR). ASSR requires the patient to be asleep and quiet, whereas CAEP is better for awake adults.

• Question: Does a report showing non-organic results get used against someone in court?

  • Response: It's less about "slapping their wrist" for being naughty and more about using formulas to determine true entitlement and accurate compensation based on the objective objective SARA numbers.

• Question: Why use speech sounds in infants?

  • Response: It is more relevant to language development and potentially more interesting to the child than pure tones.

Cortical Auditory Evoked Potentials (CAEPs)

Learning Outcomes

• Describe the neural generators and principles to record obligatory CAEP.

• Describe the requirements to prepare patients for CAEP testing.

• Be able to label straightforward traces and analyse/interpret the results .

• Be able to identify stimulus, recording, and subject factors that affect obligatory CAEP interpretation.

• Recommend trouble shooting techniques to improve poor responses.

• Describe different clinical applications of obligatory CAEP in complex audiological cases.

• Be familiar with discriminative CAEPs.

• Apply knowledge of cortical auditory evoked potentials to accurately diagnose hearing disorders and evaluate treatment outcomes in both children and adults.

Overview

• CAEPs are another type of auditory evoked potential used by audiologists.

• They were previously mentioned in relation to:

  • Non-organic hearing loss presentations.

  • Cases where behavioural testing cannot provide reliable thresholds.

  • Auditory Processing Disorder (APD) assessment.

• CAEPs are often considered when:

  • Behavioural testing is unreliable.

  • Objective confirmation of hearing thresholds is required.

  • APD investigations are being conducted.

Auditory Evoked Potentials

Definition

Auditory evoked potentials are:

• Neural activity within the auditory system.

• Evoked by an auditory stimulus.

• Time-locked to an auditory event.

Examples of stimuli:

• Clicks

• Tones

• Speech sounds

General principle:

• Greater stimulus intensity produces larger responses.

Position of CAEPs Along the Auditory Pathway

ABR vs CAEP

Auditory Brainstem Response (ABR)

• Occurs within approximately the first 10 ms after stimulus onset.

• Generated by the brainstem.

Cortical Responses

• Generated much higher in the auditory pathway.

• Begin around 50 ms after stimulus onset.

• Later components occur around:

  • 100 ms

  • 200 ms

As neural activity is recorded from higher levels of the auditory system:

• Complexity increases

• Different cortical regions and systems interact with each other

• Attention and cognition begin to influence responses.

Characteristics of CAEPs

Larger Amplitude

Compared with ABRs:

• CAEPs have much larger amplitudes.

• Electrodes are physically closer to the neural generators.

• Responses are easier to see above the noise floor.

Cognitive Influence

As responses originate from higher auditory centres:

• Cognition contributes.

• Attention contributes.

• State of arousal contributes.

These factors are much less important for ABRs.

Exogenous vs Endogenous Potentials

Exogenous Potentials

• A product of the stimulus characteristic

• Can be recorded regardless of whether the patient attends to the stimulus.

• Example:

  • ABR

Endogenous Potentials

• Less dependent on stimulus characteristics

• Highly dependent on:

  • Stimulus context

  • Changes in the stimulus

  • Patient state

  • Attention

Responses may be reduced if the patient is:

• Sleeping

• Not paying attention

• Habituated to the stimulus

CAEPs have important endogenous influences.

Generators of CAEPs

The cortical response is generated by many regions within the brain.

Key point:

• There are numerous contributors.

• Not expected to memorise all anatomical names

• The important concept is that many brain regions influence the recorded waveform

Adult CAEP: onset response

P1-N1-P2 complex

Components

The classic waveform consists of:

P1

• First positive peak.

N1

• First negative peak.

P2

• Second positive peak.

Naming

• P = positive peak.

• N = negative peak.

The waveform is therefore:

P1 → N1 → P2

Clinical Focus

Unlike ABR:

• Precise latency measurement is less important.

• Clinicians are mainly interested in:

  • Presence vs absence of a response.

Amplitude is much larger than ABR.

Terminology

CAEPs may be referred to by several names.

• Cortical Event-Related Potential (CERP)

• Auditory Late potential (ALP)

• Slow Vertex Potential (SVP)

• P1-N1-P2

• N1-P2

Stimulus Factors Affecting CAEPs

Stimulus Type

Any transient onset stimulus may be used:

• Clicks

• Tone bursts

• Noise bursts

• Speech syllables

Longer rise/fall times are required compared with ABR:

• Approximately 10–20 ms rise time.

Responses are broadly similar across different stimulus types.

Other Possible Stimuli

The stimulus can also be:

• A gap in a tone

• A gap in noise

• An omission within a stimulus train

• A change within a continuous sound

Choice depends on the clinical application.

Clinical Context for Threshold Estimation

A major clinical use is:

Objective Threshold Estimation

Particularly when behavioural thresholds cannot be trusted.

Common situations:

• Medico-legal cases

• WorkCover cases

• Non-organic hearing loss presentations

Purpose:

• Produce an objective audiogram.

• Confirm true hearing status.

The courts often require objective evidence because behavioural audiograms may be exaggerated.

Inter-Stimulus Interval (ISI)

Effect on Response

As ISI increases:

• N1P1 amplitude increases.

• Response improves up to approximately 5 seconds.

• Improvement then plateaus.

Recommended ISI

Approximately:

• 4–5 seconds

Comparison with ABR

ABR uses much faster rates:

• Paediatric ABR ≈ 33 Hz

• Adult ABR ≈ 11 Hz

CAEP testing is therefore much slower.

Test Duration

Obtaining a full objective audiogram using CAEPs can take:

• Approximately 3 hours

Reasons:

• Slow presentation rates.

• Need for multiple frequencies.

• Need for replication.

Tonotopic Organisation

Frequency Effects

Lower-frequency sounds:

• Produce greater spread of activity (basilar membrane)

• Are processed closer to the scalp (auditory cortex)

→ Produce larger amplitude responses

Higher-frequency sounds:

• Produce responses that are generally more difficult to record.

Responses can still be obtained at high frequencies, but lower frequencies are usually easier to interpret.

Intensity Effects

Latency

Louder stimuli:

• Produce shorter latencies.

Unlike ABR:

• Relationship is not strongly linear.

• Latency remains relatively stable at high levels.

• Latency increases noticeably only near threshold.

Amplitude

Louder stimuli:

• Produce larger amplitudes.

Softer stimuli:

• Produce smaller amplitudes.

Sweeps and Averaging

Important Difference from ABR

ABR:

• More sweeps generally improve waveform quality.

CAEP:

• Over-averaging is counterproductive

Why?

• Habituation occurs.

• Attention decreases.

• Neural responsiveness reduces.

Recommended Number

• Stimuli above about 20 dBSL usually produce a clear response after 10

  • still need to replicate responses

Patient Factors Affecting CAEPs

Attention

Attention is critical.

Poor attention can reduce response quality.

Relaxation

Patients should:

• Sit still.

• Relax.

• Avoid muscle tension.

Jaw tension can create artefact.

Sleep

Unlike ABR:

• Sleep is a major problem.

Patients should remain:

• Awake

• Alert

Strategies:

• Bright room

• Movie without sound

• Reading material

• Games

Avoid:

• Dim lighting

• Situations that encourage sleep.

Maturation (Age Effects)

Latency

With increasing age:

• Latency decreases.

Amplitude

With increasing age:

• Amplitude increases.

Children

Responses are:

• Smaller

• Less mature

• More variable

Adults

Responses are:

• Larger

• Cleaner

• Easier to interpret

This developmental effect makes CAEPs useful for:

• Monitoring auditory development.

• Monitoring outcomes following intervention.

Habituation

Definition

Reduction in neuronal responsiveness following repeated stimulation.

The brain naturally learns to ignore repetitive, unimportant stimuli.

Consequences

• Reduced amplitude.

• Poorer recordings.

Minimising Habituation

Use:

• Short runs (~10 sweeps)

• Longer ISIs

• Unpredictable stimuli

Strategies:

• Alternate ears

• Alternate frequencies

• Vary presentation order

This prevents the brain from predicting upcoming stimuli.

Refractoriness

Definition:

• Decrease in neuronal excitability due to fatigue.

Effect:

• Reduced response amplitude.

Different from habituation, which is related to repeated stimulation and reduced attention.

Effects of Sedation, Alcohol and Medication

Responses may be affected by:

• Sedation

• Sleeping tablets

• Alcohol

Particularly relevant in:

• WorkCover

• Medico-legal

• Non-organic hearing loss investigations

Patients may attempt to influence results.

Sleep and sedation substantially reduce CAEP responses.

Optimising Waveforms

Stimulus Factors

Use:

• Louder stimuli

• Lower frequencies

• Longer ISIs

Patient Factors

Ensure:

• Awake

• Alert

• Eyes open

• Relaxed jaw

• No sedation

• Minimal habituation

Older patients generally produce cleaner responses.

Electrode Placement

Montage

Electrodes are placed:

• Low forehead

• Vertex (top of head; coronal line)

• Earlobes or mastoids

Practical Challenge

Hair makes obtaining low impedance difficult.

Strategies:

• Part the hair

• Use exfoliating paste

• Use impedance gel

Patients are often advised they will need to wash their hair afterwards.

Impedance

Target:

• Less than 10 kΩ

Compared with ABR:

• ABR target is usually <5 kΩ.

Most important principle:

• Electrode impedances should be balanced.

Balanced moderate impedances are preferable to one very high impedance electrode.

Patient Instructions

We're measuring your brain's electrical activity in response to sounds played through

your ears. The test is automatic, so you don't need to do anything. Testing takes a

while, so feel free to read a magazine or use this iPad to pass the time.

Patients should be told:

• They will hear sounds.

• They do not need to respond.

• The test is automatic.

• The test may take a long time.

Provide activities to maintain alertness:

• Books

• Movies with subtitles

• Nintendo Switch

• Colouring activities

• iPads

The goal is to keep the patient:

• Quiet

• Comfortable

• Awake

• Engaged

Clinical Applications

Main Applications

1. Cortical Evoked Response Audiometry (CERA)

Technique to objectively estimate hearing thresholds

Used for:

• Objective audiograms

• Non-organic hearing loss

• Medico-legal assessment

• Patients unable to complete behavioural testing

2. HearLab

Used for:

• Infants

• Hearing aid verification

• Cochlear implant candidacy assessment

3. Auditory Processing Disorder Assessment

Used to:

• Assess maturation of auditory pathways.

• Monitor changes following intervention.

Other applications were mentioned but described as more specialised.

CERA Threshold Search

Features:

• Excellent frequency specificity (250-8000 Hz)

• Good validity

  • Threshold estimates often within 5–15 dB of behavioural threshold

Typical procedure:

• Descend in 20 dB steps.

• Ascend in 10 dB steps if response is lost.

• Replicate responses.

Indicators of threshold:

• Response becomes smaller.

• Latency increases.

• Response eventually disappears.

Scale Differences: ABR vs CAEP

Important clinical warning:

CAEP amplitudes are much larger than ABR amplitudes.

If the wrong display scale is used:

• An ABR may appear flat.

• Normal hearing may be misinterpreted as profound hearing loss.

Checking the display scale is one of the first troubleshooting steps.

Troubleshooting

No Response

Check:

• Stimulus presentation

• Electrode placement

Small Response

Consider:

• Patient attention

• Drowsiness

• Habituation

Noisy Response

Consider:

• Muscle tension

• Jaw movement

• Chewing gum

• Poor electrode impedance

• Tangled leads

• Mobile phone interference

Reinstruct and relax the patient if necessary.

Cortical Auditory Evoked Potentials (CAEPs / “SARA”) – Detailed Lecture Notes

Based strictly on the provided lecture transcript only.

1. Adult Clinical Application: Non-Organic / Unreliable Behavioural Audiograms

Case 1: Jeffrey (54 years old)

History

• Referred by a medical panel for SARA testing.

• Had a hearing test previously.

• Fitted with hearing aids 6 months earlier at another clinic.

• Reports hearing aids are annoying because he hears “too much”.

• No ENT concerns.

• Constant bilateral buzzing/ringing tinnitus for 2 years.

  • Annoying but not affecting sleep.

• Worked in the transport industry.

  • Significant occupational noise exposure.

  • No hearing protection provided.

• Seeking compensation related to workplace noise exposure.

• Occasionally experiences lightheadedness when standing.

• Otherwise generally well.

Behavioural Audiogram Findings

Inconsistency 1: Speech Results vs Audiogram

Observed:

• Speech scores close to 100% at 50 dB.

• Speech scores also close to normal at 30 dB.

Interpretation:

• If speech recognition is close to 100% at 30 dB:

  • Estimated hearing thresholds around 1–2 kHz should be approximately normal.

• This is inconsistent with an audiogram suggesting severe hearing loss.

Inconsistency 2: Acoustic Reflexes

Why were reflexes considered reassuring?

• Reflexes present around 80 dB.

• Based on minimum sensation level calculations:

  • Patient should at least be hearing around 65 dB.

Therefore:

• Reflex findings do not support the severe behavioural hearing loss shown on the audiogram.

Why Was Bone Conduction Not Performed?

Reason:

• Air-conduction responses were not reliable.

• If AC responses are unreliable:

  • Bone conduction will not provide useful additional information.

• Better use of clinical time:

  • Use alternative techniques.

  • Perform objective tests.

Clinical reasoning:

Inconsistency 3: Multiple Different Thresholds at Same Frequency

Example:

• Right AC threshold at 1 kHz varied depending on technique:

  • 80 dB

  • 60 dB

  • 35 dB

Interpretation:

• A reliable audiogram should not show this degree of variation.

• Therefore:

  • Audiogram is unreliable.

  • Bone conduction would not be helpful.

Inconsistency 4: OAEs

Findings:

• OAEs present from 1–4 kHz.

Interpretation:

• OAEs suggest hearing is no worse than mild–moderate loss.

• This conflicts with severe behavioural thresholds.

2. SARA Testing Interpretation

General Principles

Reading the Trace

Clinician labels:

• Frequency tested.

• Presentation level.

Example:

• At 1 kHz:

  • Response obtained at 40 dB.

  • Response obtained at 20 dB.

  • Slight latency increase at lower level.

Interpretation:

• Increased latency near threshold is expected.

• Presence of repeatable waveform indicates response.

Estimated Hearing Status from SARA

Approximate findings:

• Around 20–30 dB at 1–2 kHz.

• Around 40–50 dB at 4 kHz.

Interpretation:

• Mild to moderate hearing loss.

Important fact:

• CAEP/SARA thresholds are generally within 5–15 dB of true behavioural threshold.

Therefore:

• Much closer to true hearing levels than many other objective tests.

Identifying a Response

Key Features

Look for:

1. Expected latency region.

2. P1

3. N1

4. P2

5. Repeatability between traces.

Important teaching point:

• Negativity (N1 region) often aligns most clearly.

• Peaks may not align perfectly.

• Repeatable negativity is often easier to identify.

Using Louder Responses as Templates

A stronger response at a higher level:

• Helps identify weaker responses near threshold.

Clinical caution:

3. Latency Behaviour in Cortical Responses

Relationship Between Level and Latency

Unlike some other tests:

• Latency remains relatively stable at louder levels.

• Latency only increases when approaching threshold.

Therefore:

• Similar latency across several loud levels.

• Delayed latency near threshold.

Clinical value:

• Helps determine when threshold is being approached.

4. Reporting Non-Organic Presentations

Example wording:

Behavioural responses:

• Moderate to severe bilateral hearing loss.

However:

• Variable responses obtained.

• Ascending technique.

• Speech testing.

• Objective tests.

All suggest behavioural responses are suprathreshold.

Reporting SARA Results

Example reporting style:

For thresholds obtained at 20 dB:

• Report as ≤20 dB.

Reason:

• Testing not performed below 20 dB.

• True threshold may actually be better.

Conservative interpretation:

5. Hearing Aid Implications

Why Were the Hearing Aids Too Loud?

Likely explanation:

• Previous clinic accepted exaggerated behavioural thresholds.

• Hearing aids fitted according to exaggerated loss.

Result:

• Excessive amplification.

• Hearing aids perceived as too loud.

Clinical Consequences

Failure to detect non-organic presentation may result in:

• Inappropriate hearing aid fitting.

• Discomfort.

• Potentially unsafe amplification.

Important Clinical Point

Patients with non-organic presentations often:

• Still have genuine hearing loss.

• Exaggeration may occur on top of real hearing loss.

Lecturer's comment:

• Sometimes patients are desperate for help.

• Exaggeration may be partly subconscious.

• Not always deliberate deception.

6. Adult Clinical Application: Intellectual Disability Case

History

Patient:

• Long-term hearing aid user through Hearing Australia.

• Previously diagnosed with moderate-severe hearing loss.

• Intellectual disability.

• Recent decline in:

  • Responsiveness

  • Attention

  • Communication

Question:

• Has hearing deteriorated?

Problem:

• Reliable behavioural audiogram could not be obtained.

Testing Challenges

Patient:

• Could only sit still for ~15 minutes.

Management:

• Used AFLW football videos on an iPad to maintain cooperation.

Testing priority:

• Answer the referral question efficiently.

Results

Only obtained:

• 1 kHz

• 4 kHz

• One ear

This limited information was enough.

Hearing Australia later confirmed:

• No significant hearing change.

Clinical conclusion:

• Hearing was not the cause of the patient's deterioration.

Why Not ASSR?

Lecturer explanation:

• ASSR:

  • Smaller amplitude.

  • More elevated relative to behavioural threshold.

  • Requires quietness/sleep.

For this adult:

• Cortical responses provided a better estimate of hearing status.

7. HearLab in Infants

Purpose

HearLab:

• Objective cortical testing in awake young infants.

• Uses speech stimuli.

• Conducted in free field.

Correlates well with:

• Infant perception of sound.

Main Uses

1. Hearing Assessment

• Assess access to speech sounds.

• Can help re-estimate audiogram.

2. Hearing Aid Verification

• Usually ~6 weeks after fitting.

• Determines whether amplification is adequate.

3. Cochlear Implant Assessment

• Determine whether hearing aids provide sufficient speech access.

• Supports referral decisions.

4. Auditory Neuropathy

• Helpful before fitting.

• More detail taught later in course.

8. HearLab Speech Stimuli

Speech sounds:

• /m/

• /g/

• Other speech phonemes spanning frequency range.

Characteristics:

• /m/ = lower frequency

• Higher-frequency phonemes represent upper frequency region.

Statistical Detection

Software evaluates:

• Repeatability.

• Consistency.

• Shape matching.

• Statistical significance.

Criterion:

• p < 0.05

If achieved:

• Response considered present.

Software is more objective than visual interpretation alone.

Why Use Speech Stimuli?

Reason:

• Goal is speech and language development.

More clinically meaningful than:

• Pure tones alone.

Question:

9. Infant Case: Eleanor

Background

• 5 weeks old.

• Recently fitted with hearing aids.

• HearLab performed at Visit 1 and Visit 2.

Visit 1 Interpretation

Findings:

• Poor access to low-frequency sounds.

• Poor access to soft mid-frequency speech sounds.

Management:

• Increase low-frequency gain.

• Increase mid-frequency gain.

Visit 2

Results:

• More responses present.

• Better access to soft speech sounds.

Outcome:

• Improved hearing aid performance.

Parent feedback:

• Felt relieved.

• Confidence in hearing aids restored.

10. Infant Case: Zu

History

• Profound SNHL diagnosed at 3 months.

• Bilateral hearing aids fitted at 4 months.

• HearLab performed at 4.5 months.

Visit 1

Results:

• No clear responses.

• No access to speech sounds despite hearing aids.

Management:

• Hearing aids adjusted.

Visit 2

Results:

• Still inadequate speech access.

Interpretation:

• Hearing aids unable to provide required amplification.

Management:

• Refer for cochlear implantation.

Importance of HearLab

Provides objective evidence that:

• Hearing aids are insufficient.

Helps families:

• Make informed cochlear implant decisions.

11. Auditory Processing Disorder (APD)

Clinical Use

Not used for threshold estimation.

Instead:

• Present suprathreshold stimuli.

• Examine maturation of auditory pathways.

Research Findings

Compared:

• APD children

• Age-matched controls

Findings:

• APD group had:

  • Later latency.

  • Smaller amplitude.

  • Responses resembling younger auditory systems.

Interpretation:

• Auditory pathways appear less mature.

Typical APD Protocol

Often:

• 500 Hz

• 4 kHz

Presented around:

• 80–85 dB

May repeat after auditory training.

Improvement indicators:

• Reduced latency.

• Increased amplitude.

Limitation

Need:

• Better normative data.

Currently:

• Used as one component of an assessment battery.

• Not a standalone diagnostic tool.

12. P300

What Is It?

Measure of:

• Attention

• Recognition of change

Occurs:

• ~300 ms after stimulus.

Indicates:

• High-level cognitive processing.

• Broad brain involvement.

Stimuli

Can use:

• Auditory

• Visual

• Other sensory stimuli

Not limited to hearing.

Method

Two stimulus categories:

Standard Stimulus

• Frequent/common stimulus.

Deviant Stimulus

• Rare/different stimulus.

Brain response to deviant stimulus:

• Much larger.

Responses are compared:

• Standard vs deviant.

Difference reveals P300.

Requirements

P300 only occurs if:

• Brain recognises the difference.

Examples:

• Different frequencies.

• Different colours.

• Different flashing patterns.

Attention is required.
If attention is elsewhere:

• P300 may not occur.

Applications

More common in:

• Neuropsychology

Used for:

• Cognitive dysfunction

• Alzheimer's disease

• Dementia

• Aphasia

• Cognitive tracking over time

Also used in research:

• Auditory perceptual skills.

13. Final Summary of Clinical Applications

Established Clinical Uses

1. Adult hearing threshold estimation.

2. Infant hearing threshold estimation.

3. Aided hearing threshold estimation.

4. Hearing aid verification.

5. Cochlear implant candidacy support.

Emerging Applications

1. Auditory Processing Disorder.

2. Cognitive tracking.

3. Neuropsychological assessment.

4. Traumatic brain injury.

Research Applications

Hyperacusis

Observed:

• Larger amplitude responses to loud sounds.

Potential use:

• Understanding mechanisms.

• Evaluating management effectiveness.

Tinnitus

Research exploring:

• Objective pitch matching.

• Site of generation.

Kahoot Exam Pearls

Cortical Response Timing

• Much later than ABR.

• Approximately 50–200 ms response window.

Inter-Stimulus Interval (ISI)

• Increasing ISI increases N1-P2 amplitude.

• Effect plateaus around 5 ms.

• Aim for approximately 5 ms ISI.

Patient Preparation

Recommended:

• Keep patient alert.

Not recommended:

• Dimly lit room.

(Unlike ABR, where sleepiness is desirable.)

Tonotopic Organisation

• Lower frequencies are processed closer to the scalp.

• Therefore produce larger cortical responses.

Over-Averaging

Problem:

• Causes habituation.

Result:

• Can be counterproductive in cortical recordings.

HearLab

Purpose

Objective cortical testing in awake infants.

Used to:

• Estimate hearing.

• Verify hearing aid fittings.

• Assess cochlear implant candidacy.

• Evaluate auditory neuropathy cases.

Procedure

Child is:

• Seated approximately 1.5 m from the loudspeaker.

• Kept awake and engaged.

Possible distractors:

• Toys

• Cartoons (without sound)

• Tablets

• Sensory toys

Avoid:

• Noisy toys

• Videos with sound.

Speech Stimuli Used in HearLab

Speech sounds:

• /m/

• /g/

• /t/

These broadly represent different frequency regions of speech.

Purpose:

• Determine whether amplified speech sounds are reaching the auditory cortex.

Emerging and Research Applications

Mentioned areas include:

• Hyperacusis research

  • Larger cortical responses to louder tones.

• Tinnitus research

  • Objective pitch matching.

  • Investigating site of generation.

Currently these remain primarily research applications.