Lec 9: BOA and OAE Applications

Clinical Applications of Behavioral Observation Audiometry (BOA) and Otoacoustic Emissions (OAEs) in Pediatrics

Overview of Pediatric Hearing Assessment Techniques

• Developmental Timeline and Testing Gaps:

  • Newborn to 4-5 Months: Electrophysiological assessments like ABR (Auditory Brainstem Response) and ASSR (Auditory Steady-State Response) are primarily used as infants at this age sleep frequently.

  • 5 to 9 Months: This represents a "gap" in formal testing. It becomes difficult to keep infants asleep for electrophysiological tests, yet a large proportion (up to 12 months) are not developmentally ready for Visual Reinforcement Audiometry (VRA).

  • 7-9 Months and Up: VRA can be attempted, but success is hit-or-miss until roughly 12 months.

  • BOA's Role: BOA helps fill the gap between 5 and 9 months by providing Minimum Response Levels (MRLs) rather than true thresholds.

Behavioral Observation Audiometry (BOA) Protocol

• Formal vs. Informal BOA:

  • Formal BOA: Conducted in a controlled environment (e.g., Royal Children’s Hospital) using two clinicians and calibrated stimuli.

  • Informal BOA: Used in challenging clinical situations (e.g., Children’s Surgical Center in Cambodia) using toys or phones to observe any reaction to sound, primarily to rule out profound deafness.

• The Two-Clinician Setup:

  • Tester 1 (Presenter): Positioned behind the infant to avoid visual cues. They present the stimulus for 2-3 seconds, measure intensity using a Sound Level Meter (SLM), and provide social reinforcement if the child turns.

  • Tester 2 (Observer/Distractor): Sits in front of the infant. Their role is to keep the child in a "nice response state" (ready but not over-stimulated) and observe subtle behavioral changes like eyes widening or stilling.

• Stimulus Characteristics:

  • Ascending Technique: Start at the level expected for normal hearing at that age and increase in roughly $10\,dB$ steps.

  • Time Gaps: Maintain long intervals of silence between presentations to allow the room to reset and the child to process the sound.

  • MRL (Minimum Response Level): BOA provides MRLs, which are super-threshold levels, not true hearing thresholds.

Infant Behaviors and Response Categories

• Reflexive Responses:

  • Auro-Palpebral Reflex (APR): A brainstem reflex elicited by loud sounds ($70\text{ to }100\,dBA$), resulting in a reflexive eyelid blink. Facial nerve activity causes this closure.

  • Moro Reflex: Found in babies under 4-6 months. Stimulus (sound or sudden movement) causes the baby to spread arms/legs and bring them back.

  • Startle Reflex: General bodily jump in response to sudden stimuli.

• Arousal Behaviors (Positive):

  • Movement increase, smiling, eyes widening, increased sucking rate, or vocalizations.

• Quieting Behaviors (Negative):

  • Stilling, holding breath, reduced sucking rate, or reduced vocalization.

• Localization Development:

  • 3 Months: Unsteady; moves towards sound in the horizontal plane only.

  • 5 Months: Straight-line localization (horizontal then vertical).

  • 6 Months: Moves head and eyes in an arc-like movement.

  • 8 Months: Fully developed localization; head moves directly to the source.

BOA Instrumentation and Frequency Correspondence

• Noisemakers:

  • Manchester Rattle: Very high frequency, roughly $8,000\,Hz$ when shaken softly.

  • Squeaky Frog/Toy: High-pitched, but lower than the rattle.

  • Shaky Egg: Mid-to-high frequency.

  • Chime Bars: Frequency-specific (e.g., Note B), but difficult to present at very soft levels.

  • Drum: Used for APR; provides a broadband loud stimulus ($70\text{ to }100\,dBA$).

• Live Voice:

  • "Ba Ba Ba": Low frequency, captures energy from nasal murmurs.

  • "Shhh": High frequency, with energy above $4,000\,Hz$.

Expected MRLs for Normal Hearing Infants

• Note: High-frequency improvement is typically faster than low-frequency improvement in infants.

Otoacoustic Emissions (OAEs) in Pediatrics

• TEOEs (Transient Evoked OAEs): Used frequently in newborn screening (Victoria, Australia) because they are fast and provide a "Pass/Refer" result. They can rule out all but a mild hearing loss ($35\,dB$ or better).

• DPOEs (Distortion Product OAEs): Common in clinical diagnostics. They provide frequency-specific information. The main distortion product formula is $2f_1 - f_2$. They are generally present if hearing is $45\,dB$ or better.

• Clinical Considerations:

  • Middle Ear Status: Requires clear middle ears. If Type B tympanograms are present, OAEs will be absent.

  • Pressurized DPOEs: Used for Type C tympanograms to compensate for negative pressure and attempt to elicit a response.

  • Amplitudes: Infant OAE amplitudes are significantly larger than those in adults, making them easier to record if the child is still.

  • Auditory Neuropathy: Diagnosed when ABR is absent/abnormal but OAEs are present (indicating normal cochlear hair cell function but faulty nerve transmission).

Interpretation and Triage

• Diagnostic Power of Combining Tests:

  • BOA and OAEs are used together for children who cannot perform VRA (e.g., ASD, developmental delay).

  • If BOA MRLs are normal and OAEs are present, clinicians can often rule out significant loss and schedule a distant review.

  • If results are inconsistent or show elevated MRLs/absent OAEs, a sedated ABR at a tertiary center (e.g., Royal Children’s) is the last resort.

• Reporting Phrases:

  • "Minimum response levels obtained via BOA suggest no worse than a [Mild/Moderate] hearing loss."

  • "Absent DPOEs across 1-6 kHz suggest cochlear dysfunction in the high frequencies."

Case Study: Kirby

• Patient Profile: 9 months old.

• Risk Factors: Aminoglycoside antibiotics (10 days), Special Care Nursery (2 weeks).

• Symptoms: Limited babbling, not turning to sound, prefers solitary play.

• Test Results:

  • VRA: Could not be conditioned.

  • Tympanometry: Type A (Normal).

  • OAEs: Absent DPOEs bilaterally (1-6 kHz).

  • BOA: Normal MRLs in the lows ($30\,dBA$ for "ba ba ba"); elevated in the highs ($65\,dBA$ for "shhh" and "rattle").

• Conclusion: Results suggest a potential high-frequency hearing loss. Management involves an ASAP review for further VRA attempts to establish true thresholds.

BOA & Paediatric OAE Applications Notes

Learning Outcomes

• BOA:

  • Recall basic auditory sensitivity across the first months of life

  • Follow the steps to conducting BOA

  • Justify what test stimuli are chosen and how they are presented

  • Interpret BOA test results and recognise what other information is required for interpretation

  • Describe why BOA has limitations as a hearing threshold measurement technique

• OAE applications:

  • Justify when OAEs are of clinical relevance in paediatric populations and what hearing conclusions may result

How you can implement this knowledge into your clinical practice:

• Recognise when BOA might add useful information to the test battery, and use past BOA results to inform future clinical testing and management

• Recognise situations in which OAEs could be useful in a paediatric appointment and interpret OAE results in conjunction with other tests.

Behavioural Observation Audiometry (BOA)

What is BOA?

BOA is:

• A behavioural assessment technique used mainly in infants/young children

• Used when formal threshold testing is not possible

• Used to obtain minimum response levels (MRLs)

• NOT a true threshold test → A suprathreshold assessment only

Why BOA is Needed

Gap Between Electrophysiological Testing and VRA

Electrophysiological assessment

Possible in very young infants.

Problem

Once infants reach:

• ~4–5 months and older

It becomes difficult to:

• Keep them asleep during ABR/ASSR appointments.

VRA

Can usually start from:

• ~7–9 months onward

However:

• Many infants are not developmentally ready for VRA before 12 months.

Therefore:

There is a testing gap approximately between:

• 5–6 months to 8–9 months

BOA helps fill this gap.

Formal vs Informal BOA

Formal BOA

• Usually involves:

  • Two clinicians

  • Structured presentation of sounds

  • Observation of infant responses

• Can involve a formal BOA room setup.

Informal BOA

Examples:

• Playing favourite songs/videos

• Using phone sounds

• Observing spontaneous reactions to sounds

Used especially:

• When children are difficult to test

• When VRA unsuccessful

• In ASD/developmentally delayed children

Importance of BOA

• Rule out profound deafness

• Rule out significant hearing loss

• Provide information about responses to sound

• Help determine urgency of review

• Help reduce parental concern

Infant Responses to Sound

Infants respond differently to sound compared with:

• Older children

• Adults

Infants:

• Often do not respond behaviourally to soft sounds

• Require louder sounds to elicit behavioural responses

• May still have normal hearing despite lack of response to softer sounds

Infant development from 0-9 months

behaviours in response to hearing sound

1. Reflexive

Auro-palpebral Reflex (APR)

• Brainstem reflex

• Elicited by loud sound

• Causes reflexive eyelid closure/blink

• Mediated via facial nerve

Examples of stimuli:

• Loud clap

• Dog bark

• Sudden loud sound

Moro Reflex

Occurs in infants:

• < 4–6 months

Triggered by:

• Loud sound

• Sudden movement

• Feeling of falling

Response:

• Arms/legs extend outward

• Then come back inward

Other Reflexive Responses

• General Startle

• Eye-turn

2. Arousal

Positive/additive behaviours:

• Smile

• Increased movement

• Eye widening

• Increased sucking rate

• Vocalisations

3. Quieting

Negative/reduced behaviours:

• Stilling (Reduced movement)

• Holding breath

• Reduced sucking rate

• Reduced vocalisations

Auditory Localisation Development

~ 3 Months

• horizontal plane movement (unsteady)

~ 5 Months

• Straight line localisation

• Horizontal then vertical localisation

~ 6 Months

• Arc-like head and eyes movement toward sound

~ 8 Months

• Localisation should be fully developed

• Direct head and eyes turns to sound source

Hearing sensitivity

As children develop, there are improvements in:

• behavioural thresholds

• thresholds in noise

• frequency discrimination

• temporal discrimination

• localisation

Key elements of auditory processing

Infant Behavioural Responses vs Age

As age increases (by age 12 months):

• Behavioural responses improve

• Gradual improvements in showing their sensitivity to sounds to within ~10 dB of ‘real’ thresholds

• High frequency improvement is faster than low frequency improvement

• Maturation of brain structure and function depends on

  • Experience

  • Interaction with the environment

A newborn with normal hearing may:

• Ignore 20 dB sounds behaviourally

• Need 70–100 dBA sounds to react

Parents may incorrectly think:

• Infant cannot hear

Clinicians may need to counsel parents regarding this.

Expected response lv./MRLs of normal hearing

Stimuli

1. Noisemakers = equipment of known frequency/pitch

2. Live voice

Live Voice Stimuli

“mm”

• Low-frequency stimulus

• Nasal murmur

• Good for low-frequency hearing assessment

“sh”

• Mid/high-frequency stimulus

• Most energy above 4000 Hz

• Good for high-frequency hearing assessment

Noise Makers

Manchester Rattle

• Contains grains

• Soft shake corresponds to ~8000 Hz

• Louder shaking lowers frequency emphasis

Drum

• Low-frequency stimulus

Squeaky Toy/Frog

• Higher-frequency stimulus

• Not as high as rattle

Shaky Egg

• Mid/high-frequency

• Can be tricky

Chime Bars

• Frequency-specific stimuli

BOA set up

Tester 1

• Present sound stimulus

• Observe responses

• Reinforce responses

• Measure sound levels using sound level meter

Tester 2

• Distract infant appropriately

• Maintain response state

• Observe subtle responses — Communicate with tester 1

Presentation Guidelines

• Stimuli should be randomised

• Avoid habituation

• Present stimuli for 2–3 seconds minimum

• Leave long silent gaps between presentations

Positioning

Tester 1:

• Positioned behind infant

• Infant should not see tester in peripheral vision

Air Movement

Infants may respond to:

• Air movement

• Non-auditory cues

Clinician should minimise these cues.

Ascending Technique

Procedure:

1. Start around expected normal-hearing response level for age

2. Present stimulus

3. If no response:

   • Wait for silence

   • Increase intensity

4. First response level = MRL

No strict dB step size:

• ~10 dB increases suggested

Sound Level Meter

Settings:

• FAST

• dBA

Placed near tester 1 for easy access.

Important!!

Auro-palpebral Reflex (APR) Testing

Procedure

• Use drum + drumstick

• Single loud bang

• Aim:

  • ~70–100 dBA (Normal APR range)

Important

Warn caregiver beforehand:

• Avoid caregiver startling

• Prevent invalid infant response interpretation

APR Interpretation

Normal:

• Loud sound elicits blink reflex

APR behaves like reflex result:

• ~15 dB sensation level

Example:

• 90 dB drumbeat → blink

• Suggests at least one ear hears:

  • 75 dB or better

Can help:

• Rule out profound hearing loss

Situations Where BOA is Used

Parent Concerns

Examples:

• Loud wedding exposure

• Concern despite passing newborn screening

Maternal Child Health Referrals

• Failed “Bell test” (Bell test considered invalid/unreliable)

Early referal as Risk Factors for Hearing Loss

• FH/ meningitis

  • Missed electrophysiological assessment window

Children Not Ready for VRA

• Too young

• Developmentally delayed

• ASD

• Cannot condition for VRA

BOA + OAEs

BOA and OAEs complement each other.

Together they can:

• Rule out significant hearing loss

• Eliminate all but mild loss in some cases

Referral for Sedated ABR

Consider when:

• BOA abnormal/inconsistent

• OAEs abnormal/inconsistent

• VRA unsuccessful

• Thresholds still required

BOA Interpretation

BOA can:

• Rule out hearing loss greater than MRLs obtained (in at least one ear)

• Suggest elevated hearing levels

• Suggest possible frequency configuration

  • Elevated responses for one frequency range, when responses at other frequency ranges were at expected levels → hearing loss in a particular frequency range

BOA cannot:

• Provide true thresholds

• Reliably comment on hearing in separate ears

  • Correct localisation to stimuli on each side is possible even if unilateral loss

  • ability to localise can give a bit more confidence that hearing is similar between ears

BOA Management Principles

Children are rarely discharged based only on BOA.

Usually:

• Additional testing needed

• Follow-up/review needed

Informal BOA

informally observe response to sound

Useful when:

• Child running around

• Cannot sit for VRA

• Difficult to condition

Common Informal BOA Method

Play favourite sound/video:

• Very soft volume

• Observe reaction

Examples:

• Favourite YouTube videos

• Cocomelon

Clinical Value

Can:

• Reduce clinician / parental concern

• Determine urgency of review

• Support referrals to other developmental pathways

Paediatric OAEs

Used in:

• Newborn hearing screening

• Infant diagnostic batteries

• Difficult-to-test children

• Complementary assessment tool

TEOAEs vs DPOAEs

TEOAEs

• Faster

• Often used in screening

• Can provide quick pass/refer result

DPOAEs

• More frequency-specific

• Provide detailed frequency information

OAEs in Newborns

Advantages:

• Babies quiet/still

• Easier to test

• Large OAE amplitudes in newborns

Important Limitation

A newborn can:

• Pass newborn screening

• Have present OAEs and ABR

• Still have mild sensorineural hearing loss

Screening primarily targets:

• Moderate or greater hearing loss

OAEs in Infant Diagnostic Test Batteries

• Reliably recordable

• OAE amplitude in normally hearing newborns is greater

• Confirm the ABR, tympanometry and other frequency-specific test results (i.e. ASSR)

• Presence of OAEs in the absence of an ABR (or grossly abnormal ABR) is suggestive of auditory neuropathy

OAEs in Difficult-to-Test Children

• Obtain a non-behavioural assessment of cochlear function in children who are unable to complete behavioural testing

• A broad understanding of a child’s likely hearing ability → determine the urgency of review timeframes

  • TEOAEs Present → rule out worse than mild hearing loss (>35 dB)

  • DPOAEs Present → rule out worse than moderate hearing loss (>45 dB at tested frequencies)

• Run tymps prior to OAE testing

  • Type B → OAEs expected absent / not useful

  • Type C → Pressurised DPOAEs

• Tricky for very active children as they need to be still and silent

  • watch the OAE screen as it records

  • watch their favourite TV show on mute

OAE Interpretation

Signal-to-Noise Ratio (SNR)

Criterion:

• ≥6 dB difference required

Noise Floor

High noise floor:

• Invalid test

• Responses may be hidden under noise

Possible causes:

• Child movement

• Environmental noise

Kirby Case Study

History

9-month-old Kirby:

• Aminoglycoside antibiotics ×10 days

• Special care nursery ×2 weeks

• Limited babbling

• Not turning to sounds

• Appears to ignore sounds

Red Flags

• Aminoglycoside exposure

• Limited babbling

• Not turning/responding to sounds

• SCN admission

Testing

VRA

Attempted but:

• Child would not condition

Tympanometry

Results:

• Type A bilaterally

DPOAEs

Results:

• Absent bilaterally 1–6 kHz

Interpretation:

• Suggest possible hearing loss

• Cannot diagnose hearing loss using absent OAEs alone

BOA Findings

Responses

• Head turns present

• Age-appropriate localisation

Interpretation

Low frequencies:

• Within expected levels

High frequencies:

• Elevated MRLs

Suggestive of:

• Possible mild high-frequency hearing loss

Reporting Language

Recommended wording:

• “Suggests”

• “Potential”

• “Elevated hearing levels”

Avoid:

• Definitive diagnosis

• Defining conductive vs sensorineural loss at this stage

Management

• Review ASAP

• Continue attempting VRA

• Obtain true thresholds over multiple sessions if needed