the nal-nl2 prescription method for hearing...
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Harvey Dillon NAL-NL2
Sing Soc Audiol Professionals 1
The NAL-NL2 prescription method for hearing aids
Harvey Dillon, Gitte Keidser, Teresa Ching,
Matt Flax, Scott Brewer
HEARing CRC
National Acoustic Laboratories, Australia
Audiology Online
June 2012
Talk structure
Temporal resolution
Frequency resolution
Intelligibility in noise
OAEsDead
regionsThresholds
NL2 formula
NAL-NL2 derivationIntelligibility
Age
Gender
Experience
Binaural
Language
Speed
NAL NL1
(?)
Amplification rationales
Children
Infants
RECD
nHL eHL
Gain preferences
Outcomes
Loudness NAL-NL1 deficiencies
Severe profound
CR
The Fitting Process
Harvey Dillon NAL-NL2
Sing Soc Audiol Professionals 2
Measure hearing thresholds (dB HL)
Enter into manufacturer software
Adult Child
Measure hearing thresholds (dB HL or dB SPL)
Measure individual RECD (or estimate from age)
Enter into manufacturer software
Verify with real ear measurement
(hearing aid auto adjusted to approximate prescription)
Adjust amplification to better match prescription
(hearing aid auto adjusted to approximate prescription)
Adjust hearing aid in coupler via computer to better match prescribed coupler gain
Prescription goals
Prescribe hearing aids to:Prescribe hearing aids to:
Make speech intelligibleMake speech intelligible Make loudness comfortableMake loudness comfortable
Prescription affected by other things Prescription affected by other things –– localization, localization, –– tonal quality, tonal quality, –– detection of environmental sounds, detection of environmental sounds, –– naturalness. naturalness.
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Sing Soc Audiol Professionals 3
Hearing aids amplify , so ….Hearing aids amplify , so ….
How much amplification?How much amplification?
Gain
50 dB SPL
65 dB SPL
Frequency
80 dB SPL
The lolly shop
Deriving NAL-NL2
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Sing Soc Audiol Professionals 4
The rationale for NAL proceudresThe rationale for NAL proceudres
Maximize calculated speech intelligibility , Maximize calculated speech intelligibility , butbut
Keep total loudness less than or equal to normalKeep total loudness less than or equal to normalKeep total loudness less than or equal to normalKeep total loudness less than or equal to normal
NAL-NL1 (1999) empirical studies
psychoacoustic studies
speech intelligibility models
NAL-NL2
Compare
Deriving optimal gains Deriving optimal gains -- step 1step 1
Speech spectrum & level
Gain-frequency
Loudness model
Normal loudness
Compareresponse
Amplified speech spectrum
Loudness model
Loudness (hearing impaired)
Audiogram
Intelligibility model
Intelligibility achieved
Inverted hearing loss profiles used
Rejection criterion :-30<= G <=60 , where G is the slopesum(H(f))/3 <=100 , where f is in the set {0.5, 1, 2} kHz
The audiograms
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Sing Soc Audiol Professionals 5
The audiograms, continued
Deriving optimal gains Deriving optimal gains -- step 1step 1
Audiogram 1 Speech level 1 Optimal gain frequency response
Audiogram 1 Speech level 2 Optimal gain frequency response
Audiogram 1 Speech level 3 Optimal gain frequency response
Audiogram 2 Speech level 1 Optimal gain frequency response
200 audiograms x 6 speech levels 1200 gain–frequency responses, each at 20 frequencies from 125 Hz to 10 kHz
Overall prescription approachOverall prescription approach
Theoretical predictions
Psychoacoustics
Assumptions, rationale
Final formula
Adjust
Empirical observations
Speech science
Compare
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Sing Soc Audiol Professionals 6
MultiMulti--dimensional equation:dimensional equation:
A neural networkA neural network
H250 H500 H1000 H2000 H8k SPL
G250 G500 G1000 G2000 G8k
The two key ingredientsThe two key ingredients1.1. A loudness modelA loudness model2.2. An intelligibility modelAn intelligibility model
Speech spectrum & level
Loudness model
Normal loudness
CompareGain-frequency response
Amplified speech spectrum
Loudness model
Loudness (hearing impaired)
Audiogram
Intelligibility model
Intelligibility achieved
Calculating loudnessCalculating loudness
Loudness model of Moore and Glasberg (2004)Loudness model of Moore and Glasberg (2004)Allowance for hearing loss
Sumacrossbands
Totalloudness
Calculateloudnessper band
Loudness per band
Filtering intoauditory bands
Excitationlevel
External &middle ear
Free field speech level
Input to cochlea
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Speech intelligibility
Freq
1/3
octa
ve S
PL
30
Importance: 0.001 0.002 0.003 0.002
x x x x
Freq
Audibility: 5 16 17 0... ... ... ...
= 0.30
= = = =
0.005 0.032 0.051 0... ... ... ...
Speech Intelligibility IndexSpeech Intelligibility Index
SII =SII = ∑ A∑ Aii IIii
Sum
SII SII ∑ A∑ Ai i IIii
But intelligibility gets worse if we make speech too loud!
Audibility Importance
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Speech intelligibility also depends on … Speech intelligibility also depends on … Level distortion Level distortion
Normal hearing people perform poorer at Normal hearing people perform poorer at high speech levelshigh speech levels
tor
Speech level (dB SPL)Leve
l dis
tort
ion
fact
0
1
730 140
SII = SII = ∑ A∑ Ai i IIi i LLii
Level distortion factor
The transfer function
40
60
80
100
nt
Co
rrec
t
Nonsense syllables
Sentences
0
20
40
0 0.2 0.4 0.6 0.8 1
Speech Intelligibility Index (SII)
Per
cen Nonsense syllables
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1400 - 5600 Hz
corr
ect
60
80
100
MF MS SF SS
Observed and Predicted performance
Sensation level (dB)
Per
cent
0
20
40
12 24 36 12 24 36 12 24 36 12 24 36
Ching, Dillon & Byrne, 1998
SubjectsSubjects
20 adults with 20 adults with normal hearingnormal hearing
55 adults with 55 adults with sensorineural sensorineural
Audiogram
el (
dB
HL)
-20
0
20
hearing losshearing loss–– mild to mild to
profoundprofound–– Experienced Experienced
hearing aid hearing aid usersusers
Frequency (Hz)
Hea
ring
thre
shol
d le
ve
250 500 1000 2000 4000 8000
40
60
80
100
120
Speech perceptionSpeech perception Stimuli: Filtered speechStimuli: Filtered speech
–– CUNY sentencesCUNY sentences–– VCV syllablesVCV syllables
Shaping:Shaping:–– POGO prescriptionPOGO prescription
20
40
60
80
evel (
dB
SP
L)
HP7 HP14 HP28 LP7LP14 LP28 LP56
p pp p Conditions:Conditions:
–– Quiet at high and low Quiet at high and low sensation levelssensation levels
–– Babble Noise Babble Noise Headphones: Headphones:
Sennheiser HD25Sennheiser HD25
0
20
250 500 1000 2000 4000 8000
Frequency (Hz)
Le
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VCV
ect
0 6
0.8
1.0
Audibility and Speech intelligibility Audibility and Speech intelligibility –– H.I. H.I.
Calculated SII
Pro
po
rtio
n c
orr
e
LP7: QLP7: NLP14: QLP14: NLP28: QLP28: NLP56: QLP56: NHP28: QHP28: NHP14: QHP14: NHP7: QHP7: N0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
Deficit = SDeficit = Sansiiansii -- SIISIIeffeff
40
60
80
100
nt
Co
rre
ct
Deficit = 0.6 - 0.4
= 0.2
0
20
40
0 0.2 0.4 0.6 0.8 1
Speech Intelligibility Index (SII)
Per
cen
SIIeff SIIansi
VCV deficit vs CUNY deficitVCV deficit vs CUNY deficit
0.05
0.10
0.15
0.20
0.25
SIIe
ff
R=0.77
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30
VCV SIIansi-SIIeff
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
CU
NY
SIIa
nsi-S
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Intelligibility and audibilityIntelligibility and audibility
1
30Sensation level (dB)
m
p
BKB, VCV and CUNY
BKB VCV CUNY
Q
Optimizer results: 3 data sets
Q&N
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Desensitisation for hearing lossDesensitisation for hearing loss
0 40.50.60.70.80.9
1
ve a
ud
ibili
ty 020406080
00.10.20.30.4
0 20 40 60
Sensation level (dB)
Effe
cti 80
100120
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120
Hearing threshold (dB HL)
m p
aram
eter
Psychoacoustics
Why measure only pure tone thresholds?Why measure only pure tone thresholds?
Other measurementsOther measurements
Outer hair cell function Outer hair cell function –– clickclick--evoked otoacoustic emissionsevoked otoacoustic emissions
Frequency resolution Frequency resolution –– psychophysical tuning curvespsychophysical tuning curves–– cochlear dead regions cochlear dead regions –– TEN testTEN test
Cognitive abilityCognitive ability AgeAge
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Healthy PTC Healthy PTC –– no dead regionno dead region
Psychophysical tuning curve
SP
L)
90
100
110 A29
Masker
Masker Frequency (Hz)
Mas
ker
Leve
l (dB
S
500 1000 1500 200050
60
70
80
90
Signal
Poor PTC: Dead region at 4 kHzPoor PTC: Dead region at 4 kHzPsychophysical tuning curve
SP
L)
110
120
Masker Frequency (Hz)
Mas
ker
Leve
l (dB
1000 2000 3000 4000 500080
90
100
Dead regionsDead regions
NAL-NL1 only allows for hearing loss desensitization on average
RIP
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OffOff--frequency listening: TEN testfrequency listening: TEN test
e vi
brat
ion
Frequency or position
Basi
lar
mem
bran
e
Based on Moore (2004)
Threshold Equalizing Noise (TEN)
TEN and PTC (non) agreementTEN and PTC (non) agreement
2 kHz2 kHz TEN: AliveTEN: Alive TEN: DeadTEN: Dead
PTC: PTC: 6060 11
TEN
uncertain
1Tip in placeTip in place
PTC:PTC:Tip shiftedTip shifted
44 33
PTC uncertain 1
2
2
1
1
Psychoacoustic correlations Psychoacoustic correlations –– 4 kHz4 kHzMatrix Plot (Prof and Psy 11 March 09.sta 659v*75c)
HL
PTC Q10
OAE strength
TEN elevation
Cognition
Age
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Psychoacoustic correlations Psychoacoustic correlations –– 2 kHz2 kHzMatrix Plot (Prof and Psy 11 March 09.sta 659v*75c)
HL2k
PTC2k_Q10
C2kC2k
El2k
Cognition
AgeLim
Can we better predict Can we better predict intelligibility if we use intelligibility if we use psychoacoustic results?psychoacoustic results?psychoacoustic results?psychoacoustic results?
Deficit (VCV & CUNY), HL, Q10, OAE, TEN, Cog, & Age: 5600 Hz low passes-SIIeff (VCV Avg(QH QL N) LP5600)
SIIdes-SIIeff (CUNY Avg(QH QL N) LP5600)
L56HL
Q10 LP56
COAE L56
EL LP56
Cogni tion
AgeLim
Harvey Dillon NAL-NL2
Sing Soc Audiol Professionals 16
Yes, a little Yes, a little –– speech speech deficit increases as deficit increases as frequency selectivity gets frequency selectivity gets broaderbroader
But not once we But not once we fully build HL into fully build HL into the SII prediction the SII prediction
Correlations
HL 500 PTC5_Q10
OAE 500
TEN 500
Cognit Age
HL 500 -- -0.70 0.04 0.56 -0.38 0.26PTC5_Q10 -0.70 -- -0.06 -0.48 0.33 -0.17OAE 500 0.04 -0.06 -- -0.10 -0.05 -0.05TEN 500 0.56 -0.48 -0.10 -- -0.35 0.04Cognition -0.38 0.33 -0.05 -0.35 -- -0.45A 0 26 0 17 0 05 0 04 0 45
500 HzHL 1k PTC1k
_Q10OAE 1k
TEN 1k
Cognit Age
HL 1k -- -0.63 -0.36 0.46 -0.38 0.30PTC1k_Q10 -0.63 -- 0.30 -0.10 0.23 -0.17OAE 1k -0.36 0.30 -- -0.18 0.20 -0.20TEN 1k 0.46 -0.10 -0.18 -- -0.13 0.10Cognition -0.38 0.23 0.20 -0.13 -- -0.45Age 0 30 -0 17 -0 20 0 10 -0 45 --
1 kHz
Age 0.26 -0.17 -0.05 0.04 -0.45 -- Age 0.30 0.17 0.20 0.10 0.45
HL 4k PTC4k_Q10
OAE 4k
TEN 4k
Cognit Age
HL 4k -- -0.84 -0.60 0.58 -0.43 0.41PTC4k_Q10 -0.84 -- 0.50 -0.49 0.33 -0.23OAE 4k -0.60 0.50 -- -0.31 0.44 -0.40TEN 4k 0.58 -0.49 -0.31 -- -0.45 0.38Cognition -0.43 0.33 0.44 -0.45 -- -0.45Age 0.41 -0.23 -0.40 0.38 -0.45 --
4 kHz2 kHz
HL 2k PTC2k_Q10
OAE 2k
TEN 2k
Cognit Age
HL 2k -- -0.79 -0.65 0.53 -0.40 0.35PTC2k_Q10 -0.79 -- 0.49 -0.47 0.36 -0.25OAE 2k -0.65 0.49 -- -0.36 0.35 -0.36TEN 2k 0.53 -0.47 -0.36 -- -0.38 0.15Cognition -0.40 0.36 0.35 -0.38 -- -0.42Age 0.35 -0.25 -0.36 0.15 -0.42 --
CorrelationsCorrelations
PTCAge
HL
Cognit
OAE
TEN
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Multiple regressionMultiple regression
PTC
including HL causes:including HL causes:
correlations between age and PTC / OAE / TEN to disappearcorrelations between age and PTC / OAE / TEN to disappear
correlations between cognition and PTC / OAE / TEN to disappearcorrelations between cognition and PTC / OAE / TEN to disappear
Age OAE
TEN
Cognition
HL
Likely intermediate effectsLikely intermediate effects
? PTC
OAE
Cognition
Mechanical
Age
Cardio-vascular
IHC
Noise
OAE
TEN
HL
OHC
Stria
Why are hearing thresholds so useful?Why are hearing thresholds so useful?
H i Speech
Frequency selectivity
Temporalresolution
Hearing thresholds
Speech Perceptionproficiency
Central auditory processing
OtherAge
Cognitive ability
Harvey Dillon NAL-NL2
Sing Soc Audiol Professionals 18
Factors affecting prescription
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Gain; 187 adults, medium input level
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Source: Keidser et al., 2008
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Sing Soc Audiol Professionals 19
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Adjustments to prescription to allow for experience
68
1012
men
t NewExperienced
-8-6-4-20246
0 20 40 60 80 100 120
Hearing threshold (dB HL)
Gai
n a
dju
stm
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Adjustments to prescription to allow for experience
68
1012
men
t
New
Experienced
Experienced
-8-6-4-20246
0 20 40 60 80 100 120
Hearing threshold (dB HL)
Gai
n a
dju
stm Experienced -
New
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Gain preference over time
N = 11
Source: Keidser et al. (submitted)
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Sing Soc Audiol Professionals 20
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
0.5
1
1.5
atio
n f
rom
ef
erre
d a
t 65
d
B
Smeds et al. 2006
Zakis et al. 2007
Gain; adults, low and high input levels
-2
-1.5
-1
-0.5
0
Pre
ferr
ed g
ain
dev
iN
AL
-NL
1 re
gai
n p
r ed
B S
PL
in
d
50 80
Input level in dB SPL
Output level
Adults, NL2Children, NL2
NAL-NL1
Desired gain
Gain and compression; adults vs children
Input level
Adults, NL2
Age dependent gain
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Adults – congenital or acquired?
-4
-2
0
evia
tio
n
(dB
)
-14
-12
-10
-8
-6
Pre
ferr
ed g
ain
de
fro
m N
AL
-RP
LFA HFA
Congenital(N=15)Acquired(N=28)
Harvey Dillon NAL-NL2
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The maximum C
Compression
Limiting compression for severe/profound hearing loss(Fast compression)
Source: Keidser et al., 2007
NAL-NL2 prescribes
creating sound valueTM
0
50
100
H 2
4
6
log2�
�
����� ������������f
125
�
�
�����
1.0
1.5
2.0
2.5
3.0
Ca
NAL NL2 prescribes different compression for slow and fast compressors for those with high degrees of hearing loss
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Compression ratio preferences: severe and profound hearing loss
0.8
0.9
1.0
1.1
LF b
and
1:1
45 50 55 60 65 70 75 80 85 90
Average HTL in LF band (dB HL)
0.2
0.3
0.4
0.5
0.6
0.7
Ave
rage
1/C
R in
L
Source: Keidser, Dillon, Dyrlund, Carter, and Hartley (2007)
1.8:1
3:1
Gain preference by aid configuration (N = 187)
Bilateral loudness correction
Bilateral loudness correction too large – supported by newer
data (e.g. Whilby, 2006; Epstein & Florentine, 2009)
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New bilateral loudness correction
3
4
5
6
7
riat
ion
(d
B)
0
1
2
3
0 20 40 60 80 100 120
Input level (dB)
Gai
n v
a
National Acoustic Laboratories, Sydney, Australia Keidser and Dillon
Effect of language
Gain at each frequency depends on importance of each frequency
Low frequencies more important in tonal Low frequencies more important in tonal languages
Two versions of NAL-NL2Tonal languages
Non-tonal languages
15
20
25
30
35
40
tion gain in dB
NAL‐NL1
Male, exp, non‐tonal
Male, exp, tonal
Tonal versus non-tonal language
0
5
10
15
100 1000 10000
Insert
Frequency in Hz
Harvey Dillon NAL-NL2
Sing Soc Audiol Professionals 23
RECD in infants (own mold; HA2)
15
20
25
30
35
CD
_4
k
0.60.8
2.04.0
6.08.0
20.040.0
60.080.0
200.0400.0
Age (months)
-5
0
5
10
15
RE
C
• New features in NAL-NL2– Different gain-frequency response shape and
higher compression ratios
– Different compression ratios for fast and slow compressors (severe/profound hearing loss)
Summary
– Gender dependent gain
– Age dependent gain
– Gain adaptation for new hearing aid users
– Language dependent gain (tonal vs non-tonal)
Examples of prescriptions
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Example audiogram: moderate sloping
303540
n (
dB
)
250125 500 1k 2k 4k 8k
0
20
Frequency (Hz)
HL)
50 dB
05
10152025
100 1000 10000
Frequency (Hz)
Inse
rtio
n G
ain
40
60
80
100
120
Hea
ring
thre
shol
d (d
B
65 dB
80 dB
303540
n (
dB
)
250125 500 1k 2k 4k 8k
0
20
Frequency (Hz)
HL) 50 dB
Example audiogram: flat 60
05
10152025
100 1000 10000
Frequency (Hz)
Inse
rtio
n G
ain
40
60
80
100
120
Hea
ring
thre
shol
d (d
B
65 dB
80 dB
303540
n (
dB
)
250125 500 1k 2k 4k 8k
0
20
Frequency (Hz)
HL)
50 dB
Example audiogram: steeply sloping
05
10152025
100 1000 10000
Frequency (Hz)
Inse
rtio
n G
ain
40
60
80
100
120
Hea
ring
thre
shol
d (d
B
65 dB
80 dB
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Sing Soc Audiol Professionals 25
25
30
35
n (
dB
)
250125 500 1k 2k 4k 8k
0
20
Frequency (Hz)
HL)
50 dB
Example audiogram: extreme ski-slope
0
5
10
15
20
100 1000 10000
Frequency (Hz)
Inse
rtio
n G
ain
40
60
80
100
120
Hea
ring
thre
shol
d (d
B
65 dB
80 dB
25
30
35
n (
dB
)
250125 500 1k 2k 4k 8k
0
20
Frequency (Hz)
HL) 50 dB
Example audiogram: reverse sloping
0
5
10
15
20
100 1000 10000
Frequency (Hz)
Inse
rtio
n G
ain
40
60
80
100
120
Hea
ring
thre
shol
d (d
B
65 dB
80 dB
Figure 5. Specific loudness for A-1 through A-4 based on a 65 dB international long-term average speech spectrum input in quiet. Overall loudness is shown to the right of the prescriptive method in the legends (NH designates normal hearing).
Johnson & Dillon, JAAA, 2011
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Figure 5. Specific loudness for A-1 through A-4 based on a 65 dB international long-term average speech spectrum input in quiet. Overall loudness is shown to the right of the prescriptive method in the legends (NH designates normal hearing).
Johnson & Dillon, JAAA, 2011
Figure 7. Overall loudness of each prescriptive method averaged across the five sensorineural hearing losses (A-1 through A-5) based on a 65 dB international long-term average speech spectrum input in quiet.
Johnson & Dillon, JAAA, 2011
Figure 8. Average Speech Intelligibility Index (SII) value for speech in quiet across the five sensorineural hearing losses for each prescriptive method using both the ANSI S3.5-1997 and the National Acoustic Laboratories SII methods. Also shown is the SII transformed value into a predicted speech recognition score (% correct) for the Connected Speech Test (Cox et al, 1987) using the transfer function of Humes (2002).
Johnson & Dillon, JAAA, 2011
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We measure several times,
T Ching, NAL, CRC HEAR
NAL & DSL groups have
equal language outcomes
Relationships between variables in NAL-NL2
REDD
N
BWC
WBCT
REUG
Bi-uni Gender
Age
ExperienceRECD
MLE
Aid type
I/O
Vent Tube
UCT
CR
Comp speed
Language DepthRECD
AC
BC'
ABG
BC
REIG REAG
RESR
CG
MLE
SSPL2cc
Limitingtype
SSPLES
ESCD
Blue = User i/p
Grey = internal variable
Red = effect of saturation
Dash-dot = alternatives
Green = stored data
AC'
ESG
Transducer
Taking the pressure off prescription ……
The trainable hearing aid
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Sing Soc Audiol Professionals 28
Trainable Aid
Aid user adjusts settings...
Dillon et al (2006)
Zakis et al (2007)
Trainable Aid
Process repeats for other sounds
Trainable Aid
After training...
...preferred settings are automatically applied
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Training gain, CR, CT.
15
20
25
30
n (
dB
) CRGain
0
5
10
30 40 50 60 70 80 90
Input level (dB SPL)
Gai
n
CT
“A challenge for the profession is to devise fitting procedures that are scientifically defensible and the challenge for thethe challenge for the individual audiologist is to choose the best procedures from whatever are available”
Denis Byrne, 1998
Acknowledgements
creating sound valueTM
This research was financially supported by the HEARing CRC established and supported under the Australian Government’s Cooperative Research Centres Program
www.hearingcrc.org
www.nal.gov.au