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The application of cortical auditory evoked potential recordings in infant hearing aid fitting. Maryanne Golding, Harvey Dillon, Suzanne C Purdy*, John Seymour, Wendy Pearce, Lyndal Carter, Richard Katsch, Mridula Sharma* * , Katrina Agung, Kirsty Gardner-Berry. National Acoustic Laboratories

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slide1

The application of cortical auditory evoked potential recordings in infant hearing aid fitting

Maryanne Golding, Harvey Dillon, Suzanne C Purdy*,

John Seymour, Wendy Pearce, Lyndal Carter, Richard Katsch,

Mridula Sharma**, Katrina Agung, Kirsty Gardner-Berry

National Acoustic Laboratories

Cooperative Research Centre for Hearing

*Speech Science, The University of Auckland, New Zealand

** Audiology, Macquarie University

evaluation of aided functioning in infants

Cochlear implant needed

Confirmation of fitting

Fine-tuning needed

Evaluation of aided functioning in infants

Universal new born screening

Early fitting of hearing aids

Need for an evaluation method

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

Objective hearing aid evaluation for:

  • young infants
  • difficult-to-test people
why cortical responses to evaluate hearing aid fitting in infants
Why cortical responses to evaluate hearing aid fitting in infants?
  • Reliably present in awake young infants
  • More likely to correlate well with perception
  • Can be elicited by a range of speech phonemes – close to desired outcomes
  • Stimuli handled reasonably by hearing aids
  • Can be very frequency specific if needed
adult

P2

N1

5.0

P1

2.5

µV

0.0

-2.5

0.0

100.0

200.0

300.0

400.0

500.0

600.0

Adult
infants

15.0

10.0

µV

5.0

0.0

-5.0

-100.0

0.0

100.0

200.0

300.0

400.0

500.0

600.0

ms

Infants

P

N

maturational effects on cortical evoked response morphology
Maturational effects on cortical evoked response morphology

Ponton et al (2000)

  • N=8-16 per grand mean
  • Cz site
  • stimulus = 10 click train, 2 ms ISI @ 65 dB SL
  • rate = 1.3/s
maturation with time in sound

Maturation with time “in sound”

Ponton and Eggermont 2007

auditory system maturity
Auditory system maturity

Ponton and Eggermont (2007):

Latency matures consistent with the time “in sound”

Sharma (2002):

Provided implantation occurs by 4 years of age

grand average n 16 infants

+

MM

OO

OR

UU

EE

AH

SH

SS

-

400.00

600.00

0.00

200.00

ms

Grand Average n = 16 infants
number of infants n 20 with significantly different cortical responses to pairs of stimuli
Number of infants (N=20) with significantly different cortical responses to pairs of stimuli

m vs t m vs g t vs g

Based on MANOVA at Cz, 101 to 500 ms post-onset, in eight bins each 50 ms

why not obligatory cortical responses

high skill level needed to read responses

Why not obligatory cortical responses?
  • variable shape across ages
  • variable shape with auditory experience
  • variable shape from person to person
  • variable shape from time to time (state of person, especially sleepiness)
  • stimulus
  • Inter-stimulus interval

An automated method of response detection and response differentiation

desirable characteristics

Hotellings T2

Desirable characteristics
  • No reliance on a template
  • Able to use information from contributing portions of waveform
  • Able to discount non-contributing portions of waveform
analysis using hotellings t 2 statistic
Analysis using Hotellings t2 statistic
  • Divide each record into 50 ms time bins
  • Average data points within each time bin
  • Use these averages as variables in Hotellings t2 analysis
  • Result is probability of the waveform being random noise

X3

Voltage

Time

X = a1X1 + a2X2 + ........ + a9X9

Test: is there any set of weighting coefficients for which X ≠ 0?

infants hotellings versus experts

adults

Infants: Hotellings versus experts

Normal hearing infants aged 7 to 16 months

loudness growth above threshold
Loudness growth above threshold

Hellman & Meiselman, 1990

cortical responses and functional performance

Cortical responses and functional performance

Do cortical responses tell us about real-life auditory performance?

slide40

Parent’s Evaluation of Aural/oral performance in

Children (PEACH) Questionnaire

  • Parents are asked to describe their baby’s aural/oral
  • skills based on real-life experiences (listening in quiet
  • and in noise and alertness to environmental sound)
  • Scores are assigned based on the number of observed
  • behaviors and how frequently these occur.
  • Final overall score of 0 – 40 can be calculated (and
  • reported as a percentage).
slide41

Functional deficit versus cortical score

* All aided children

rs =0.60; n=24; p = 0.001

* SN only

rs=0.61; n=12; p = 0.02

* MD only

rs=0.82, n=5; p = 0.04

* AN only

rs=0.36; N=7; p = 0.22

slide42

Reducing measurement variability (random electrical signals)  Speeding up measurements Increasing validity of interpretation

capacitive coupling 50 hz
Capacitive Coupling 50 Hz

Passive Electrodes

capacitive coupling 50 hz1
Capacitive Coupling 50 Hz

Active Electrodes

capacitive coupling 50 hz2
Capacitive Coupling 50 Hz

Active Electrodes

Passive Electrodes

finding thresholds with cortical responses

Finding thresholds with cortical responses

What does an absent cortical response mean?

slide48
Cortical auditory evoked responses traditionally used for objective assessment of hearing thresholds in adults
  • In 1965 Hallowell Davis showed good agreement between cortical and pure tone thresholds in children
  • For many years cortical response audiometry has been regarded as the “gold standard” for objective electrophysiological hearing assessment
slide50

From: Rickards, F. et al (1996) Cortical Evoked Response Audiometry in

noise induced hearing loss claims. Aust. J. Otol. 2 (3)

clinical applications of corticals
Clinical applications of corticals
  • For finding thresholds (when awake)
  • Determining whether speech sounds are audible
    • aided or unaided
    • for patients who can’t respond reliably by behavioral testing e.g., infants, multiply disabled people.
clinical implications of corticals

Morphology normal for age

All is well

Morphology abnormal for age

Repeat test

Low residual noise

Re-check fitting;

Consider all options

High residual noise

Draw no conclusion !

Clinical implications of corticals

Significant response is obtained to speech at 65 dB SPL

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

clinical implications of corticals cont

Review HF gain or loss estimate

Review mid-freq gain or loss estimate

Review LF gain or loss estimate

Draw no conclusions from missing response !

Clinical implications of corticals (cont)

No /t/ response

Mixed results (and noise is low)

No /g/ response

No /m/ response

Mixed results (and noise is high)

application for auditory neuropathy an
Application for auditory neuropathy (AN)
  • 15% of babies found to have hearing loss at birth in NSW have AN
  • Management unclear (no device, hearing aid or cochlear implant)
  • Rance showed close relationship between cortical response in older children and benefit from hearing aids
  • Gap detection worse in people with AN
  • Investigating gap detection by cortical responses
ah 2 second duration
/Ah/ 2 second duration

0msG.avg

5msG.avg

10msG.avg

20msG.avg

50msG.avg

5.0

2.5

Offset

0.0

Onset

µV

Gap

-2.5

-5.0

-7.5

-350.0

150.0

650.0

1150.0

1650.0

2150.0

2650.0

ms

summary
Summary

Cortical responses

  • For checking the audibility of speech sounds
  • Indicate the maturity of the auditory system
  • Automatic detection as good as experts
  • Residual noise size critical
  • For checking hearing thresholds when the patient is awake
slide59
Thanks for listening

www.nal.gov.au