HEARLab training Harvey Dillon, Bram Van Dun, Lyndal Carter, Kirsty Gardner-Berry HEARing CRC National Acoustic Laboratories (NAL) With

HEARLab training

Harvey Dillon, Bram Van Dun, Lyndal Carter, Kirsty Gardner-Berry

HEARing CRC

National Acoustic Laboratories (NAL)

www.hearingcrc.org

With thanks to John Seymour, Suzanne Purdy,

Maryanne Golding, Hsiuwen Chang, Barry Clinch, Lars Kirk

3 September 2010 - Version 1 NAL: Dillon, Van Dun, Carter, Gardner-Berry

INTRODUCTIONINTRODUCTION

NAL: Dillon, Van Dun, Carter, Gardner-Berry

The need for a new The need for a new measurement toolmeasurement tool


Evaluation of aided functioning in infantsEvaluation of aided functioning in infants

Universal new born screeningUniversal new born screening

Early fitting of hearing aidsEarly fitting of hearing aids

Need for an evaluation methodNeed for an evaluation method

Confirmation Confirmation of fittingof fitting

Fine-tuning Fine-tuning neededneeded

Cochlear Cochlear implant implant neededneeded


So baby, how does it sound?So baby, how does it sound?

Objective hearing aid Objective hearing aid evaluation for: evaluation for:

• young infantsyoung infants• difficult-to-test difficult-to-test

peoplepeople


Language at 6 m onths after im plantat ionW ilks lambda=.71507, F(2, 28)=5.5785, p=.00914

< 12m 12m +

Im plant age c ategory

40

50

60

70

80

90

100

110

120

PLS

-4 standard scores

Cov ar iate means :MonFit: 10.97917

CA 6P_A C CA 6P_EC

Why the rush?Why the rush?Language ability 6 months after implantationLanguage ability 6 months after implantation


(Computed f or c ov ar iates at their means )

V ertic al bars denote 0.95 c onf idenc e interv als

F itt ing age c ategory

PLS

-4 standard scores

< 6m > = 6m60

70

80

90

100

110

120

< 6m > = 6m

Cov ar iate means :F6A V 3FA : 57.11296

A 6P_A C A 6P_EC

Pre s : N AL Pre s : D SL

Significant effect of age of fitting: p = 0.001*

Early intervention leads to better language development at 6 months after fitting (n=90)


Why use Why use corticalcortical responses? responses?


Why cortical responses to evaluate hearing Why cortical responses to evaluate hearing aid fitting in infants?aid fitting in infants?

• Reliably present in awake young infants Reliably present in awake young infants

• More likely to correlate well with More likely to correlate well with perceptionperception

• Can be elicited by a range of speech Can be elicited by a range of speech phonemes – close to desired outcomesphonemes – close to desired outcomes

• Stimuli handled reasonably by hearing aidsStimuli handled reasonably by hearing aids

• Can be very frequency specific if neededCan be very frequency specific if needed


FUNDAMENTALS FUNDAMENTALS OF OF

CORTICAL CORTICAL RESPONSESRESPONSES


The end of the roadThe end of the road


Auditory cortex orientationAuditory cortex orientation






Hudson, 2009

+

-

+


Cortical responses in adults with Cortical responses in adults with normal hearingnormal hearing


AdultAdult

2.5

5.0

300 400

µV

0 100 200 500 600

0.0

-2.5

P2P2

N1N1P1P1


Adult grand mean waveforms at CzAdult grand mean waveforms at Cz

Tones

Speech


Cortical responses in infants with Cortical responses in infants with normal hearingnormal hearing


InfantsInfants

ms500 600300 400100 200-100 0

µV

0

5

10

-5

PP

NN


/t/ black/g/ blue/m/ green500 Hz red2000Hz pink

Infant CAEPs to various stimuli


Repeated measures ANOVA (N= 20)stimulus (p<.0001), montage (n.s.), stimulus x montage (p=0.0223)

P1 Latency


P1 amplitude P1 amplitude

Repeated measures ANOVA (N= 20)stimulus (p<.0001), montage (p = 0.0006), stimulus x montage (n.s.)


Latency versus ageLatency versus ageFunction = 271-106*log10(12*X) -7.8*(log10(12*X))^2+6.94*(log10(12*X))^3

0.1 0.2 0.5 1 2 5 10 20 50

Age (years)

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

La

ten

cy o

f P1

(m

s)

Sharma et al

NAL data


HEARLAB: TECHNICAL HEARLAB: TECHNICAL OVERVIEWOVERVIEW


Practical implementation of Practical implementation of cortical testing: HEARLabcortical testing: HEARLab

DisclosureDisclosure: NAL will get a royalty for each unit sold.: NAL will get a royalty for each unit sold.

Thank you:Thank you: The HEARLab development team – The HEARLab development team – Teck Loi, Barry Clinch, Isabella Tan, Ben Rudzyn, Teck Loi, Barry Clinch, Isabella Tan, Ben Rudzyn, Lyndal Carter, Dan Zhou, Scott Brewer Lyndal Carter, Dan Zhou, Scott Brewer





In combination with:

Ambu Blue Sensor Ndisposable electrodes

2. Differential Amplification

• Two electrodes detect the “response (signal)” to varying degrees plus “noise”, with reference to a third electrode,

• By inverting the electrical activity at one of the two main sites, and finding the difference between them, some noise cancellation occurs and thesignal size is increased,

• This improves the signal-to-noise ratio (SNR) to some degree.


2. Differential amplification

Inverting

Non-inverting+

-

Ground


From: Hall, J.W. (1992) Handbook of Auditory Evoked Potentials

(Excerpts from Figure 5-13)

Electrode input: + - Ground

Pre-amp Active Reference GroundNon-inverting Inverting Reference

3. Averaging

Averaging is the single most powerful technique for improving SNR

For repeated auditory stimulation, the neurons of the auditory system will be activated in the same sequence, at the same point in time,

We can say then that this neuronal activity is “time-locked” to the presentation of the stimulus.


3. Averaging


• Repeated stimulation with the same sound is required to view the auditory response (i.e., to have an adequate signal-to-noise ratio),

• The number of stimulations required depends on the size (i.e., amplitude) of the response.

3. Averaging


4. Filters

• A device which permits some frequencies through and not others, • High Pass (low freq) filters reject lower energy and Low Pass (high freq) reject energy above.

The most appropriate filters are those which preserve thefrequency region of the response and exclude others


4. Filters


• Choice of stimulus depends on our clinical objective and from where in the auditory system we are recording.

• Responses from the early parts of the auditory system are best generated using very brief stimuli such as a “click”. Responses from late in the auditory system can be generated using tones, speech sounds or clicks.

• Stimuli may be delivered by headphone, insert earphone,bone conduction or loud speaker.

5. Stimuli


0 5 10 15 20 25 30-1

0

1G

Am

pli

tud

e

Time (ms)

0 5 10 15 20 25 30-1

0

1M

Am

pli

tud

e

Time (ms)

0 5 10 15 20 25 30-1

0

1T

Am

pli

tud

e

Time (ms)

Three speech sounds: /m/ /g/ /t/

0

10

20

30

40

50

60

70

125

200

315

500

800

1250

2000

3150

5000

8000

Frequency (Hz)

1/3

oct

ave

spec

tra

(dB

SPL)

/m/

/g/

/t/

5. Stimuli


Automatic detection of cortical Automatic detection of cortical responsesresponses


Why automated method?Why automated method?

• variable shape across agesvariable shape across ages• variable shape with auditory experiencevariable shape with auditory experience• variable shape from person to personvariable shape from person to person• variable shape from time to time (state of person, especially sleepiness)variable shape from time to time (state of person, especially sleepiness)• variable shape with stimulusvariable shape with stimulus• Variable shape with inter-stimulus intervalVariable shape with inter-stimulus interval

high skill level needed to read responsesNAL: Dillon, Van Dun, Carter, Gardner-Berry

Desirable characteristicsDesirable characteristics

• No reliance on a templateNo reliance on a template

• Able to use information from Able to use information from contributing portions of waveformcontributing portions of waveform

• Able to discount non-contributing Able to discount non-contributing portions of waveform portions of waveform

Hotellings T2


• Each response* is divided into 50 ms time bins (50 – 500 ms)Each response* is divided into 50 ms time bins (50 – 500 ms)

• The data points are averaged within each time bin to form 9 variablesThe data points are averaged within each time bin to form 9 variables

Time

Vo

ltag

eResponse detection (Hotelling’s T2)

Stimonset


Calculates the probability that a mean value ofany linear combination of the 9 variables wassignificantly different from zero.

Hotelling’s T2 is :

At least equal to, if not more able, than the “composite” examiner to differentiate a CAEP from random noise at sensation levels of 10 dB or more

Response detection (Hotelling’s T2)


Effect of sensation level, hearing Effect of sensation level, hearing loss, and unrelated EEG or muscle loss, and unrelated EEG or muscle

noisenoise


Residual noise levels (for 100 epochs)Residual noise levels (for 100 epochs)

0.60.8

1.01.2

1.41.6

1.82.0

2.22.4

2.6

Residual noise level (uV)

0

10

20

30

40

50

60

70

80

90

100

No

of

ob

s

0 5

Awake adults

2.22.4

2.62.8

3.03.2

3.43.6

3.84.0

4.24.4

4.64.8

Residual noise level

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

No

of

ob

s

Awake infants But also

larger responses


Growth of amplitude with SLGrowth of amplitude with SL

10 20 30

Sensation level (dB)

0

2

4

6

8

10

12

14

16

18

N1 to P

2 amplitude (uV

)

Normal hearing infants

Normal hearing adults

Hearing impaired adultsHearing impaired infants


Conclusions: Detecting cortical Conclusions: Detecting cortical response presenceresponse presence

• Large responses are more easily detectedLarge responses are more easily detected

• Response amplitude grows with sensation levelResponse amplitude grows with sensation level

• Response amplitude at low SL is larger for Response amplitude at low SL is larger for people with sensorineural hearing loss that for people with sensorineural hearing loss that for people with normal hearingpeople with normal hearing

• Responses are more easily detected when Responses are more easily detected when residual noise is low (<3.4 residual noise is low (<3.4 µV for infants; < 1.5 µV for infants; < 1.5 µV for adults)µV for adults)


CLINICAL USE OF CLINICAL USE OF HEARLABHEARLAB


Equipment configuration andEquipment configuration andtest environmenttest environment


Equipment configurationEquipment configuration


Equipment configurationEquipment configuration


CAEP room set-up at the CAEP room set-up at the National Acoustic LaboratoriesNational Acoustic Laboratories

Free Field Speaker

Baby sits on parent’s lap in the centre of the room or in a high chair.


CalibrationCalibration

Calibrate each time major changes occur in test environment.

For details refer to HEARLab manual, Section 4.1


Ambient noise measurementAmbient noise measurement

In general the ambient noise level should not exceed 35 dB A.

For details refer to HEARLab manual, Section 5.3.3


Test environment


(highlights from HEARLab manual, Appendix A: ‘Practical aspects of CAEP testing with infants’)

• Make the test environment ‘child friendly’.

• Provide a chair that is big enough for both parent and child.

• Use washable covers/towels on the chair.

• Have a separate container on hand to collect items that require cleaning.

• Avoid fluorescent lighting, cell phones.

• Do not place mains-powered devices close to the child.

• Place floor markers indicating the position of equipment after calibration.

Before the appointmentBefore the appointment


Before the appointment



• Provide parents with information. This will save time during the assessment.

• Ask about the child’s sleeping routines. They should be awake during testing.

• Dress the child with layers of clothing that can be easily removed.

Preparation for testingPreparation for testing


From: Hall, J.W. (1992) Handbook of Auditory Evoked Potentials


Electrode equipmentElectrode equipment


Keeping electrodes on the baby Keeping electrodes on the baby using a headbandusing a headband


Preparation for testing



• Have all equipment ready before the child arrives.

• Change hearing aid batteries and check operation.

• Ask parents to switch off mobile phones.

• Connect to the child and don’t physically ‘stand over’ the child while doing skin prep.

• Prepare the skin firmly but not too hard with cotton bud and medical gel.

• Alcohol wipes is not needed and not recommended for delicate infant skins.

• A headband can be very helpful for keeping electrodes in place.

• Avoid contact of electrode cables with child as (s)he may pull them away.

Conducting a measurementConducting a measurement


HEARLab


Two options:

ACA: “Aided Cortical Assessment”

• Free field • Speech sounds• Can be tested aided or unaided• Focused on infants

CTE: “Cortical Threshold Evaluation”

• With insert phones• Tone-bursts• Only unaided• Focused on adults

Starting up HEARLab


Double click icon

First screen that pops up:

More detailed informationin HEARLab manual,

Chapter 3.

Adding a new client



Searching for a client


New assessment


Configuring ACA


Configuring ACA


New run


Impedance check


Acquisition of data


Acquisition of data

Acquisition of data

Ongoing EEG

Most recent epoch

Cumulative averages

p-value automatic detection



Acquisition of data

p-value automatic detection

Residual noise level

The indicator lights should be GREEN

p-values must be < 0.05for detection of cortical

! This means that in 5% of the casesa false detection is possible !


Result window


Result windowWere responses detected?

Averaged responses

Statistical analysishistory

Distraction techniques



• Do not obstruct the line of sight to the loudspeaker when testing free field.

• Only use noiseless toys, appropriate to the age, and which are easily cleanable.

• Try to keep children awake, but not too active.

• DVDs on a screen! Bubbles! Following slides will show a lot of distraction items.

• Eating and drinking is possible, including breast feeding.

• If the child is quiet, the distractor can move out of sight.

Keeping the baby awake!Keeping the baby awake!


Tools for keeping baby quiet, alert, awakeTools for keeping baby quiet, alert, awake


(More) tools for keeping baby quiet, alert, awake(More) tools for keeping baby quiet, alert, awake


(Yet more) tools for keeping baby quiet, alert, awake(Yet more) tools for keeping baby quiet, alert, awake


Yes!!


Head support

Cortical threshold estimation

- is very similar to ACA

- has not been verified clinically with infants yet


Finishing upFinishing up


Finishing up


• Results can be printed.

• Follow infection guidelines to wash or dispose of used equipment.

INTERPRETATION OF INTERPRETATION OF THE RESULTSTHE RESULTS

&& CLINICAL CLINICAL

APPLICATIONSAPPLICATIONS


Estimating hearing thresholds in Estimating hearing thresholds in non-responsive adultsnon-responsive adults

Elderly infirm – stroke, dementiaElderly infirm – stroke, dementia

Workers’ compensationWorkers’ compensation


Good agreement between CAEP and Good agreement between CAEP and audiometric thresholds in awake adultsaudiometric thresholds in awake adults

Tsui, Wong & Wong 2002 NAL: Dillon, Van Dun, Carter, Gardner-Berry

Cortical threshold vs behavioural Cortical threshold vs behavioural threshold - adultsthreshold - adults

0 20 40 60 80 100 120

Behav io ra l thresho ld (dB HL)

0

20

40

60

80

100

120

Co

rtical th

resh

old

(dB

HL

)

r2 = 0.77; r = 0.88, p < 0.0001; y = 9.7 + 0 .914*x


outliers in about 7% of threshold estimates!(reported byseveral studies)

Cortical thresholds minus Behavioral thresholds

68% +5 dB

84%+10 dB

91%+15 dB


Conclusions: Estimating behavioural Conclusions: Estimating behavioural thresholds in hearing-impaired adults thresholds in hearing-impaired adults

• Cortical thresholds overestimate behavioural Cortical thresholds overestimate behavioural thresholds by 2.4 dB, on averagethresholds by 2.4 dB, on average

• Standard deviation of cortical – behavioural threshold Standard deviation of cortical – behavioural threshold differences is 6.3 dBdifferences is 6.3 dB

• About 7% overestimates hearing thresholds severely About 7% overestimates hearing thresholds severely (by 20 dB or more).(by 20 dB or more).

• Applications: hearing compensation, clients unable to Applications: hearing compensation, clients unable to respondrespond


Cortical potentials to assess Cortical potentials to assess speech audibility for infantsspeech audibility for infants


Clinical implications of corticalsClinical implications of corticals

Significant Significant response is response is obtained to obtained to speech at 65 speech at 65 dB SPLdB SPL

No significant No significant response is response is obtained to obtained to speech at 65 speech at 65 dB SPL or to dB SPL or to speech at 75 speech at 75 dB SPLdB SPL

Morphology Morphology normal for agenormal for age

Morphology Morphology abnormal for abnormal for

ageage

Low residual Low residual noisenoise

High residual High residual noisenoise

All is wellAll is well

Repeat testRepeat test

Re-check fitting;Re-check fitting;

Consider all optionsConsider all options

Draw no conclusion !Draw no conclusion !


Noisy results - chewingNoisy results - chewing


Clinical implications of corticals (cont)Clinical implications of corticals (cont)

No /t/ No /t/ responseresponse

Draw no conclusions from Draw no conclusions from missing response !missing response !

Mixed results Mixed results (and noise is (and noise is

low)low)

No /g/ No /g/ responseresponse

No /m/ No /m/ responseresponse

Review HF gain Review HF gain or loss estimateor loss estimate

Review mid-freq Review mid-freq gain or loss gain or loss

estimateestimate

Mixed results Mixed results (and noise is (and noise is

high)high)

Review LF gain or loss Review LF gain or loss estimateestimate


Hearing loss at birth ….. for parentsHearing loss at birth ….. for parents

Parental denial

Working towards a solution

Pessimism and

hopelessness

Unaided testing at

conversational levels

Aided testing at

conversational levels


Detection of corticals in infants

However, some caution is recommended.

For speech sounds exceeding 10 dB Sensation Level

23% of evoked corticals are NOT present / detected

This means that any audiological decisions should not be made based on cortical measurements alone!


CASE STUDIESCASE STUDIES


Case 1

• Age at aided cortical testing– Visit 1

6 weeks old (Initial hearing aid fitting day)

– Visit 23 months old

No cortical responses, and the results helped the parents accept

the need for cochlear implants


Tone-burst ABR (Estimated levels in dB nHL)

500 Hz 1000 Hz 2000 Hz 4000 Hz

Right >95 >95 >95 >95

Left >95 >95 >95 >95

Estimated Audiogram (dB HL) at Visit 1

500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 85 90 95 95

Left 85 90 95 95


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 90 100 105 105

Left 90 100 105 105


Visit 1

Increase gain at all frequencies

P < 0.05 ? …. No


Visit 2


• The infant received bilateral cochlear implants at 5 months of age.

• Email from the baby’s parents ~ “Thank you so much for the information

you gave us on the previous testing as it helped us with our decision to proceed with the implants.”


Case 2


13 weeks old – Visit 2

17 weeks old– Visit 3

21 weeks old

• Hearing aid fitting at 8 weeks of age

No cortical responses, even after hearing aids have been increased in gain for the third time and the parents don’t want a

cochlear implant for their baby



500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 90 80 80 85

Left 85 75 75 95


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 100 90 90 95

Left 95 85 85 95


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 100 100 100 100

Left 100 100 100 100


Visit 1



Visit 2

Right aidedLeft aided



Visit 3


• The parents still believe that their baby boy can be oral by using hearing aids.

• They are hoping to see that their baby can benefit from more powerful hearing aids.

• The baby’s hearing aids were changed from Siemens Explorer 500 P to Phonak Una SP after Visit 3.


Case 3


4.5 months old

– Visit 25.5 months old


Corticals provided reassurance about the baby hearing well


Tone-burst ABR (Estimated levels in dB nHL)

500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 40 DNT 60 70

Left 40 DNT 70 80


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 30 40 55 65

Left 30 45 65 75


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 40 45 55 65

Left 40 50 65 75NAL: Dillon, Van Dun, Carter, Gardner-Berry

Visit 1

Increase low- and mid-frequency gain


Visit 2


Email from mother:

“We feel very relieved, as our faith has been restored in the hearing aids as a result of what we discovered from the results.”


Case 4


8 months old – Visit 2

9 months old

• Hearing aids have been increased in gain two weeks before the second visit.


Too few significant cortical responses, and the aid gain was

increased, resulting in more cortical responses



500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 45 50 55 55

Left 45 55 65 55


500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 55 50 55 55

Left 55 55 65 55


Visit 1 Visit 2


Case 5

• Age at testing: 4.5 years

• Multiple disabilities

• A reliable behavioural audiogram has not yet been obtained.

A case where cortical testing was not possible


• She was moving all the time.


At her quietest state, but this only lasted for a few seconds.


• Cortical testing at 8 months of age, nine days after the initial hearing aid fitting

A case where the unaided /m/ was present but the aided /m/

was absent.


Case 6

Estimated Audiogram

500 Hz 1000 Hz 2000 Hz 4000 Hz

Right 40 35 40 45

Left 40 35 40 45


AidedUnaided


Hearing Aid Coupler Gain at 65 dB SPL Input

250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz

<0 0 7 15 20

* Both hearing aids are set the same.


Auditory neuropathyAuditory neuropathy


WP ASA 2004

250 500 750 1000 1500 2000 3000 4000 6000 8000

0

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110

HE

AR

ING

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LS

FREQUENCY (Hz)

ABR

28/8/03 - NR

ABR ABR (CM only)(CM only)



WP ASA 2004

250 500 750 1000 1500 2000 3000 4000 6000 8000

0

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FREQUENCY (Hz)

ABR

28/8/03 - NR

CAEP

14/10/03

m g t m g t




WP ASA 2004

250 500 750 1000 1500 2000 3000 4000 6000 8000

0

10

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HE

AR

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FREQUENCY (Hz)

ABR

28/8/03 - NR

15/3/04 - NR

CAEP

14/10/03

30/3/04

ECochG 15/3/04

ECochG ECochGECochG ECochGECochG ECochGECochG

m g t m g t



(abnormal potentials only)


WP ASA 2004

250 500 750 1000 1500 2000 3000 4000 6000 8000

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HE

AR

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FREQUENCY (Hz)

ABR

28/8/03 - NR

15/3/04 - NR

CAEP

14/10/03

30/3/04

ECochG 15/3/04

VROA

29/4/04

m g t m g t

ECochG ECochGECochG ECochGECochG ECochGECochG



(abnormal potentials only)


The HEARing CRC Member Organisations

This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program


Documents

HEARLab training Harvey Dillon, Bram Van Dun, Lyndal Carter, Kirsty Gardner-Berry HEARing CRC National Acoustic Laboratories (NAL) With