Mild Hearing Loss is Serious
Business
Harvey Dillon
Sharon Cameron, Teresa Ching, Helen Glyde, Gitte Keidser,
David Hartley, Jorge Mejia
NAL, The Hearing CRC
IHCON, 2010
Slides on the NAL web site:
www.nal.gov.au
What is mild hearing loss?
• Four-frequency average (500, 1000, 2000, 4000 Hz)
hearing loss in better ear between 20 and 40
dB HL
• Self-reported disability or handicap within a
certain range
• SRT in noise loss of between 3 and 6 dB
4FAHL or 3FAHL?
Frequency Scatterplot (Spreadsheet in 30000 audiograms 2010.stw 37v*30132c)
L4FA = 9.5175+0.9136*x
120
100
80
L4FA
60
40
20
0
0
20
40
60
L3FA
80
100
120
<= 0
(0,20]
(20,40]
(40,60]
(60,80]
(80,100]
(100,120]
(120,140]
(140,160]
(160,180]
(180,200]
(200,220]
> 220
How prevalent is mild hearing loss?
How prevalent is mild hearing loss?
• Davis (1995): 16% of adult population
• Wilson (1990): 18% of adult population
• Hartley et al (in press): 34% of people aged > 50 years
Blue Mountains 4FAHL better ear
Histogram (BMHS_audiogram_edited.sta 41v*2956c)
500
400
300
No of obs
200
100
0
-10
0
Hartley et al (in press)
10
20
30
40
50
60
4FA_Better
70
80
90
100
110
120
Population older than 50
Aging population - Australia
50%
40%
30%
20%
10%
0%
2010
2020
2030
Year
2040
2050
Population aging, worldwide
0
Japan
Italy
Greece
Sweden
France
United Kingdom
Canada
Australia
New Zealand
United States of America
Hong Kong (SAR of China)
Korea, Republic of
Singapore
China (exl. SARs and
World
Viet Nam
Indonesia
India
Malaysia
South Africa
Philippines
Papua New Guinea
Percentage > 65 years
5
10
15
20
25
Cluster analysis of mild losses
0
10
20
30
40
50
60
HL in ear with better 4FA
70
80
90
250
500
1000
2000
4000
Frequency (Hz)
6000
8000
Cluster
Cluster
Cluster
Cluster
Cluster
Cluster
Cluster
Cluster
Cluster
Cluster
1
2
3
4
5
6
7
8
9
10
Mild losses for study
Frequency (Hz)
250
500
1000
2000
4000
8000
0
10
Threshold (dB hL)
20
30
40
~ Minimum loss
eligible for
government benefits
50
60
70
Mild loss (4FA=29 dB)
Mild-mod loss (4FA=39 dB)
80
90
100
~ Median loss newly
fitted in Australia
Mild losses for study
Frequency (Hz)
250
500
1000
2000
4000
8000
0
10
Threshold (dB hL)
20
30
40
50
4FA HL
60
Mild
70
Mild-mod 39 dB
80
90
100
9 dB
Moderate 49 dB
Mod-Sev
59 dB
Severe
69 dB
How common is hearing aid use amongst
those with mild hearing loss?
Penetration by hearing loss
Num berowning hearing aids
Penetration 
Num berwith hearingloss
• Penetration as a function of hearing loss
–
–
–
–
Davis (1995)
Wilson et al (1998)
Hartley et al (in Press)
Kochkin
consistent
Aid ownership by hearing loss
Ownership
Population
Percentage of people
Blue Mountains Population >55 years
100
80
60
40
20
0
5
15
25
35
45
55
65
75
85
95
105 115
4FA Hearing threshold (dB HL)
Use
Ownership
Percentage of people
100
80
60
40
20
0
5
Hartley et al (in Press)
15
25
35
45
55
65
75
85
4FA Hearing threshold (dB HL)
95 105 115
What are the characteristics of mild
hearing loss?
Characteristics of mild loss
•
•
•
•
•
•
•
•
Threshold elevation √
Loss of OHC/OAE
Loss of frequency resolution – TEN, PTC, FRI
Loss of temporal (envelope) resolution
Loss of fine temporal information
Loss of spatial processing
Loss of SRT in noise
Increased disability and handicap
Loss of active process in cochlear:
OHC and OAE
10
5
0
-5
-10
-15
OAE at 2 kHz (dB SPL)
-20
-25
-30
-35
-20
0
20
40
60
HL at 2 kHz (dB)
80
100
120
Loss of frequency resolution
FRI
A
A
FRI (dB)
f
60
50
40
30
20
10
0
-10
-20
-30
0
Ching & Dillon (unpublished data)
f
4 kHz
20
40
60
HTL (dB HL)
80
100
120
Frequency resolution
AFRI ( dB)
60
350 Hz
40
20
0
- 20
0
20
40
60
80
100
120
HTL ( dB HL)
AFRI ( dB)
60
1 k Hz
40
20
0
- 20
0
20
40
60
80
100
120
HTL ( dB HL)
AFRI ( dB)
60
2 kHz
40
20
0
- 20
0
20
40
60
80
100
120
HTL ( dB HL)
AFRI ( dB)
60
4 k Hz
40
20
0
- 20
0
20
40
60
HTL ( dB HL)
80
100
120
Loss of temporal resolution
A
TRI
t
t
6
0
4
k
H
z
TRI(dB)
4
0
2
0
0
-2
0
0
2
0
4
0
6
0
8
0
H
T
L
(d
B
H
L
)
1
0
0 1
2
0
ATRI (dB)
Temporal resolution
60
350 Hz
40
20
0
-20
0
20
40
60
80
100
120
HTL (dB HL)
ATRI (dB)
60
1 kHz
40
20
0
-20
0
20
40
60
80
100
120
HTL (dB HL)
AT RI (dB)
60
2 kHz
40
20
0
-20
0
20
40
60
80
100
120
HTL (dB HL)
AT RI (dB)
60
4 kHz
40
20
0
-20
0
20
40
60
HTL (dB HL)
Ching & Dillon (unpublished data)
80
100
120
Loss of fine temporal information
• 20 synapses per IHC
• Synapse loss or IHC loss  reduced
averaging  temporal jitter
Inspiration:
• Bodian, Lieberman, Moore,
Pichora-Fuller, Spoendlin,
A digression into “normal”
hearing
Spatial Processing Disorder
Noise
Noise
Speech
Noise
Noise
26
Sharon
Cameron
Listening in Spatialised Noise - Sentences
(LiSN-S) Conditions
Same voices
Different voices
Same
direction
Talker Advantage
Low Cue
Spatial
Advantage
Different
directions
High Cue
Cameron & Dillon (2009)
LiSN-S Diagnostic Screen
Spatial Advantage (≡ Spatial Release from Masking)
18
17
16
15
Australia
14
Better
13
12
10
9
Nth America
8
9
8
7
6
11
10
Spatial Advantage (dB)
11
50-60
40-49
30-39
25-29
20-24
18-19
16-17
14-15
12-13
Age Group
Better
Spatial Advantage
Results profile: spatial processing disorder
Spatial processing remediation
Pre vs. Post (n=9)
LiSN-S Score
(Population Standard Deviation Units)
2
1
0
LC SRT -
p = 0.158
Talker Advantage - p = 0.981
-1
HC SRT -
p = 0.0002
Spatial Advantage - p = 0.0002
Total Advantage -
-2
-3
Pre-Training
Post-Training
3M Post-Training
-4
LC SRT
HC SRT
Talker
LiSN-S Condition
Spatial
Total
p = 0.001
Application to people with
hearing loss
Spatial hearing loss in hearing-impaired people:
LiSN-S Prescribed Gain Amplifier
Deficit in SRTn with hearing loss
Low Cue deficit (dB) = 0.0147-0.0631*x
High cue deficit (dB) = 4.0175-0.3029*x
0
-2
-4
-6
-8
R = -0.87
P = 0.000006
-10
Deficit re normal (dB
-12
-14
-16
20
Low Cue deficit (dB)
High cue deficit (dB)
25
30
35
40
45
4FAHL worse ear (dB HL)
Cameron, Glyde & Dillon, unpublished data)
50
55
60
Cause of deficit in SRTn
Talker Adv deficit (dB) = 3.9432-0.0061*x
Spatial Adv deficit (dB) = -3.4051+0.2273*x
0
2
4
6
8
10
Deficit re normal (dB
12
14
20
R = -0.86
P = 0.00001
Talker Adv deficit (dB)
Spatial Adv deficit (dB)
25
30
Cameron, Glyde & Dillon, unpublished data)
35
40
45
4FAHL worse ear
50
55
60
Talker advantage deficit versus age
Talker Adv deficit (dB) = 1.6806+0.0407*x
0
1
2
3
4
5
Talker Adv deficit (dB
6
7
8
0
10
20
Cameron, Glyde & Dillon, unpublished data)
30
40
50
Age
60
70
80
90
Binaural processing
Executive
control
CAPD
SO / IC / A1
x
x
ILD
ITD
ILD
ITD
R
L
~
Sensorineural
hearing loss
CN
CN
Loss of SNR in understanding speech
“Basic” loss of 0.6 dB per 10 dB of loss
+
Loss of Spatial release from masking of
2.3 dB per 10 dB of loss
+
Loss of Talker cue release from masking of
0.5 dB per 10 years of age
Loss of SRT in noise
Commonly 1.5 dB increase in SNR per 10 dB of hearing loss
SNR = -4 dB
1 dB / 10 dB
6
4
2
0
-2
-4
-6
-8
SRTn
-10
-12
-14
-16
-18
-20
Version 1
Version 2
-22
1.8 dB / 10 dB
Carter, Zhou & Dillon, unpublished data)
-24
-10
0
10
20
30
40
50
Test ear 4FA (500 to 4k Hz)
60
70
80
Should mild hearing loss interfere with
speech perception?
Speech and noise levels
90
Speech level (dBA)
80
70
60
SNR
50
40
30
30
40
50
60
70
80
Background noise level (dBA)
Source: Pearsons, Bennett and Fidell (1977)
90
Calculation of SII
1/3 oct level at TM
(dB SPL)
Noise = 60 dBA
Speech = 64 dBA
SIInh=0.65
SIIhi=0.46
100
80
60
40
20
100
1000
Frequency (Hz)
10000
Effective audibility
Effective audibility
1
20
40
0.8
60
0.6
0.4
80
0.2
100
0
0
10
20
30
40
50
Sensation level (dB)
60
70
Transfer function
Percent correct
SII  Percent correct
100
90
80
70
60
50
40
30
20
10
0
Connected
Speech
Test
0
0.2
0.4
0.6
SII
0.8
1
Mild losses for study
Frequency (Hz)
250
500
1000
2000
4000
8000
0
Threshold (dB hL)
10
20
30
40
50
60
70
80
Mild loss (4FA=29 dB)
Mild-mod loss (4FA=39 dB)
Predicted speech intelligibility
Normal hear
1
Mild unaided
SII
0.8
Mild-mod
unaided
0.6
0.4
0.2
Greatest problems in
noisy places !!
0
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
40
Mild unaided
Mild-mod unaided
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Predicted variation of SRTn with
hearing loss
Modified SII model predicts only 0.4 dB loss per
10 dB of hearing loss
0
Speech
level
SRT (dB)
-1
50
60
70
80
-2
-3
-4
-5
0
20
40
60
4FA hearing threshold (dB HL)
80
Modification of SII
• Assume normal hearers get 6 dB
advantage from spatial separation of
speech and noise
• Assume hearing impaired listeners lose
spatial advantage at a rate of 1.3 dB per
10 dB of loss (above SII predictions)
 total loss of SNR is 1.7 dB per 10 dB of
loss
Calculation of intelligibility
Speech
spectrum
Noise
spectrum
Sensation
Level
Effective
audibility
SII
(Information
received)
Max
Threshold
Importance
function
Percent
correct
current
Do hearing aids help people with mild
^
hearing loss?
Benefit of hearing aids
Predict increase in speech intelligibility
with
the modified Speech Intelligibility Index
1/3 oct level at TM
(dB SPL)
Calculation of aided benefit
100
100
80
80
60
60
40
40
20
20
100
1000
10000
100
Frequency (Hz)
Speech = 58 dBA
10000
Frequency (Hz)
Insertion gain (dB)
Noise = 50 dBA
1000
30
20
10
0
100
1000
10000
Speech intelligibility (mild loss)
1
• Tiny additional benefit
from directivity
0.6
SII
• Hearing aid “helps” in
quiet places
0.8
0.4
Norm hear
Direct
Omni
Unaided
0.2
0
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
Direct
Omni
Unaided
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Speech intelligibility (mild-moderate loss)
1
• Tiny additional benefit
from directivity
0.8
0.6
SII
• Hearing aid “helps” in
quiet places
Norm hear
Direct
Omni
Unaided
0.4
0.2
0
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -5.1 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
Direct
Omni
Unaided
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Speech intelligibility (moderate loss)
1
Norm hear
Direct
Omni
Unaided
0.8
SII
0.6
0.4
0.2
0
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -6.5 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
Norm hear
Direct
Omni
Unaided
60
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Speech intelligibility (moderate-severe loss)
1
Norm hear
Direct
Omni
Unaided
0.8
SII
0.6
0.4
0.2
0
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -7.7 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
Direct
Omni
Unaided
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Speech intelligibility (severe loss)
1
Norm hear
Direct
Omni
Unaided
0.8
SII
0.6
0.4
0.2
0
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR loss re n.h. = -9 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
Direct
Omni
Unaided
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Summary of benefit versus HL
Background noise level
40 dB A
Percent correct
100
80
60
40
20
0
0
Percent correct
40
60
80
4FA Hearing Threshold (dB HL)
100
60 dB A
20
80
60
40
20
0
0
Percent correct
40
60
80
4FA Hearing Threshold (dB HL)
100
80 dB A
20
80
60
40
20
0
0
20
40
60
4FA Hearing Threshold (dB HL)
80
Why don’t directional microphones help
more in noise?
(and adaptive noise reduction)
1. Impact of open fittings on directivity
Insertion gain (dB)
30
Combined path
20
10
Directional
Omni-directional
0
-10
Vent
path
Amplified
path
-20
125
250
500
1k
2k
Frequency (Hz)
DI = 3 dB  1.5 dB
DI = 10 dB  5 dB
4k
8k
Insertion gain (dB)
Frequency range of directional mic (mild loss)
50
55
60
65
70
75
80
85
90
20
10
0
100
1000
10000
Frequency (Hz)
50
60
70
80
100
100
80
80
60
60
40
40
20
20
100
1000
10000
100
Frequency (Hz)
Noise = 60 dBA
Speech = 64 dBA
1000
10000
Frequency (Hz)
Insertion gain (dB)
1/3 oct level at TM
(dB SPL)
Effect of aiding at 60 dBA (mild loss)
30
20
10
0
100
1000
10000
100
100
80
80
60
60
40
40
20
20
100
1000
10000
100
Frequency (Hz)
Noise = 80 dBA
Speech = 76 dBA
1000
10000
Frequency (Hz)
Insertion gain (dB)
1/3 oct level at TM
(dB SPL)
Effect of aiding at 80 dBA (mild loss)
30
20
10
0
100
1000
10000
2.
Impact of reverberation on directivity
(and vice versa)
Sound level (dB SPL)
90
80
Total
70
60
Reverberant
Direct
50
0
1
2
3
Distance from source (m)
4
5
2.
Impact of reverberation on directivity
(and vice versa)
Qs QmV
critical disteffective  0.057
RT60
Sound level (dB SPL)
90
80
Total
70
Direct
Reverberant
60
50
0
1
2
3
Distance from source (m)
4
5
Benefit of directional microphones
Benefit affected by:
–
–
–
–
Directivity pattern of microphone
Distance and direction of talker and noise sources
Acoustics of the room
Frequency range over which the hearing aid is
directional
– Frequency range over which the wearable has usable
hearing
– Nothing else
(OK, Measurement error!!)
Conclusion of acoustic analysis
1. People with mild loss need help in noisy places
2. Hearing aids increase the speech information
available mostly in quiet places!
3. Mics directional only where there is gain


high frequencies and lower levels
Where audibility is limited by threshold, not noise
So, objective benefit questionable, and
increasing with degree of loss, but …….
What do hearing aid users say ?
Experimental evaluation of selfreported benefit
• 400 clients sampled from national database
– 41,521 new clients fitted Feb to Sept, 2004
• Audiometric and other details obtained from clients’ files
• Questionnaire sent to clients 5 to 12 months after fitting
– International Outcome Inventory for Hearing Aids
– Plus 6 purpose-designed questions
• Non-responders followed up by phone or additional mail
to get a high response rate (effectively 86%)
Sample
distribution
Percentage of people
Hearing loss distribution
30
20
10
0
5
15
25
35
45
55
65
75
85
95
105 115
95
105 115
4FA Hearing threshold (dB HL)
Population
distribution
Percentage of people
40
30
20
10
0
5
15
25
35
45
55
65
75
85
4FA Hearing threshold (dB HL)
Usage of hearing aids
120
35%
100
80
21%
19%
60
13%
Number of clients
40
10%
20
0
None
1-4 hrs/day
>8 hrs/day
<1 hr/day
4-8 hrs/day
Q3: Daily usage
Factor analysis of questionnaire
Factor Loadings
International
Outcomes
Inventory
for
Hearing Aids
Composite benefit
Factor 1
Factor 2
Factor 3
Q1: want aids
0.69
0.30
0.21
Q2: difficulty unaided
0.70
0.41
0.25
Q3: use
0.74
-0.18
0.08
Q4: benefit
0.82
-0.32
0.00
Q5: residual difficulty
0.03
-0.76
-0.33
Q6: Worth it
0.83
-0.33
-0.00
Q7: Residual handicap
-0.29
-0.56
-0.06
Q8: Bother to others
-0.18
-0.68
-0.26
Q9: Quality of life
0.82
-0.32
0.02
Q10: Replace them
0.34
-0.15
-0.23
Q11: Face vision
-0.29
-0.42
0.74
Q12: paper vision
-0.22
-0.47
0.70
Proportion of variance
0.32
20
0.12
Composite difficulty
Vision
Effect of hearing loss on benefit
Current effect: F(3, 281)=1.1951, p=.31194
Vertical bars denote 0.95 confidence intervals
5.0
4.5
4.0
3.5
3.0
2.5
Composite benefit
2.0
1.5
1.0
10-19
20-29
30-39
4FA HL in better ear (dB HL)
40-49
If hearing loss does not determine benefit,
then what does?
Wishes And Needs Tool
1.
How strongly did you want to get hearing aids?





2.
Wanted it very much
Wanted it quite a lot
Wanted it moderately
Wanted it slightly
Did not want it
Overall how much difficulty do you have hearing when
you are not wearing your hearing aids?





Very much difficulty
Quite a lot of difficulty
Moderate difficulty
Slight difficulty
No difficulty
Difficulty hearing unaided and wish to
get hearing aids
60
50
40
30
20
10
0
1
2
3
4
5
Q2: No difficulty unaided
1
2
3
4
5
Q2: Slight difficulty unaided
60
1
2
3
4
5
Q2: Moderate difficulty unaided
Not at all
Very much
No of obs
Want hearing aids
50
40
30
Unaided difficulty
related to wish to get
hearing aids
20
10
0
1
2
3
4
5
Q2: Quite a lot of difficulty unaided
1
2
3
4
5
Q2: Very much dificulty unaided
Need increases with hearing loss
Current effect: F(3, 275)=8.5017, p=.00002
Vertical bars denote 0.95 confidence intervals
3.8
3.6
3.4
3.2
3.0
2.8
Need summary
2.6
2.4
2.2
10-19
20-29
30-39
Better ear 4FA range (dB HL)
40-49
Benefit versus need strength
Current effect: F(8, 109)=7.9109, p=.00000
5.0
4.5
4.0
3.5
3.0
+ "Q9: QOL")/4
2.5
2.0
1.5
Composite
1.0
1
1.5
2
2.5
3
Strength of need
3.5
4
4.5
5
Why don’t more people with mild hearing
loss even try hearing aids?
Factors affecting benefit experienced
(and hence the reports of others)
•
•
•
•
•
•
•
•
Degree of pure-tone loss
Self-reported disability and handicap
Acceptable Noise Level
Stigma / cosmetic concern
Manipulation and management
Age
Tinnitus
Personality ….
Personality
People more likely to acquire hearing aids are:
–
–
–
–
Open
Non-obsessive
Non-neurotic
Internal locus of control
People more likely to report benefit are:
– Extroverted
– Agreeable
Health Belief Model
People act rationally, in their best
interests, based on their beliefs
Weighing up of beliefs for and against a
health decision
Disadvantages
Advantages
Do I have
a problem?
Is it serious
enough for me to
want to remove it?
Is there a
solution
that works?
What are the
disadvantages
of the solution?
“My hearing loss is not bad enough to need them” (Kochkin, 1993)
Motivation comes from ….
Self-image
Acknowledge
loss
Expect
benefit
Experience
difficulty
Experience
handicap
Try them
Expect to
manage them
$ Cost OK
Health belief model
Selfimage
Cost
External
image
Inconvenience
Hearing aid
effectiveness
Ability to
manage
Difficulties
experienced:
frequency, severity
Hearing
loss
Health belief model
Health belief model
How can the balance of benefits to
disadvantages be improved?
Improving advantages and removing disadvantages
Problem 1
Problem 2
Problem 3
Cost
Working better
in noise
Solution 1
Solution 2
Solution 3
•
WDRC
•
Slim-tube, miniaturization
•
Feedback cancellation
•
Low-level expansion
•
Re-chargeable batteries
•
Auto telecoil
•
Frequency lowering
•
Bandwidth extension
•
Trainable responses
•
Adaptive noise reduction
•
Transient noise reduction
•
Directional microphones
Speech intelligibility
in noise
Binaural-Processing Super-directional Microphone
(Mejia et al., 2007)
Reardirectional
array
W1
W2
Q1
Binaural
beamformer
Q2
Q3
Q4
∑
K
W3
W4
∑
Masking threshold
∑
Main
direction
al signal
d = 3 ms delay
(Precedence effect)
K
Z-d
Subsidiary
signal
∑
HRTFL
HRTFR
∑
Cross-fading
process
DOA- reconstruction
Lout
Rout
Outputs with spatial
reconstruction
Super-directional microphones
Speech reception threshold in noise
Reverberant room: crit dist = 0.4m, radius = 1 m
0.0
Speech reception threshold (dB)
-2.0
-4.0
-6.0
-8.0
-10.0
-12.0
-14.0
NH
Dir
2-speaker
Mejia and Johnson, unpublished data
BF
NH
Dir
4-speaker
BF
NH
Dir
140-babble
BF
Linked binaural hearing aid technology
Female
talker
Male
talker
Listener

Hearing Aid
Children
playing
Blind-source separation binaural noise reduction
h.i.
gain most from
directivity
n.h. benefit from
re-insertion of
spatial cues
Implication: People with mild or moderate hearing loss were not making
much use of spatial cues.
Effect of super-directivity (mild loss)
1
0.6
SII
• Super-directional mic
not directional at all over a
broader and broader
range as noise levels rise
0.8
0.4
Norm hear
Direct
0.2
Unaided
Super-directional
0
Conditions:
DI = 6 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
40
Direct
Unaided
20
Super-directional
0
30
40
50
60
70
80
Background noise level (dBA)
90
So super-directivity alone is no
use ……..
What if we could achieve
directivity at low frequencies?
Effect of low-frequency directivity (mild loss)
1
0.6
SII
• Now directional over
entire frequency range in
noisy places
0.8
0.4
Norm hear
Direct
0.2
Unaided
Extended direct
0
Conditions:
DI = 3 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB
Speech intell (CST %)
30
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
40
Direct
Unaided
20
Extended direct
0
30
40
50
60
70
80
Background noise level (dBA)
90
Occlusion with closed molds
Vent or leak transmission in
Active Occlusion Reduction
Σ
-
+
Active occlusion reduction
Mejia, Dillon, & Fisher (2008)
In combination?
Active occlusion
reduction
(closed mold)
+
Superdirectivity
=
?
Low-frequency super-directivity (mild loss)
1
0.8
• Super-directivity over
entire frequency range
SII
0.6
 super-normal hearing
0.4
Norm hear
Direct
0.2
Frequency
100
1000
Extend/super
10000
0
0
30
40
80
100
120
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB
Speech intell (CST %)
Threshold (dB HL)
20
60
Unaided
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
40
Direct
Unaided
20
Extend/super
0
30
40
50
60
70
80
Background noise level (dBA)
90
Low-frequency super-directivity (mild-moderate loss)
1
0.8
• Super-normal hearing
for the median hearing aid
wearer
SII
0.6
0.4
Norm hear
Direct
0.2
Frequency
100
1000
Extend/super
10000
0
0
30
40
80
100
120
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -5.1 dB
Speech intell (CST %)
Threshold (dB HL)
20
60
Unaided
40
50
60
70
80
90
Background noise level (dBA)
100
80
60
Norm hear
40
Direct
Unaided
20
Extend/super
0
30
40
50
60
70
80
Background noise level (dBA)
90
Low-frequency super-directivity (moderate loss, 4FA
= 49.8 dB HL)
1
Norm hear
Direct
0.8
• Super-normal hearing in
very noisy places for even
a moderate-severe loss
Unaided
Extend/super
SII
0.6
0.4
0.2
Frequency
100
1000
10000
0
0
30
40
60
80
100
120
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -6.5 dB
Speech intell (CST %)
Threshold (dB HL)
20
40
50
60
70
80
90
Background noise level (dBA)
100
80
Norm hear
Direct
60
Unaided
Extend/super
40
20
0
30
40
50
60
70
80
Background noise level (dBA)
90
Adaptive noise reduction
• Gain dependent on SNR correct in
principle, but room for improvement:
– Gain reduction can reduce directional mic
effectiveness
– No point in reducing noise below threshold
– Gain increase where SNR is best is just as
important
Cost
Jump to summary
Self-fitting hearing aid
NAL-NL2
Prescription
Formula
Real-ear to
coupler difference
Automatic
Audiometer
Adjust
Hearing Aid
Australia, USA: 1 audiologist per 10,000 people
Developing countries: 1 audiologist per 500,000 people, to 1 per 6,000,000
Automatic versus manual audiometry
70
60
1 kHz
50
40
30
20
10
Automatic thresh
0
-10
-10
0
10
20
30
40
Manual thresholds (dB HL)
50
60
70
Test-retest standard deviations
Test-retest standard
deviation (dB)
5
Manual audiometry (5 dB
Hughson-Westlake)
4
3
2
RECD
Automatic audiometry (2 dB
final step size)
NALNL2
Auto
Aud
1
0
250
1000
Frequency (Hz)
4000
Adjust
Real-Ear to Dial Difference:
Standard deviation (dB)
Inter-subject standard deviations
10
9
8
7
6
5
4
3
2
1
0
100
Insert
Closed
Open
1000
Frequency (Hz)
10000
Real-Ear to Dial Difference:
Standard deviation (dB)
Inter-subject standard deviations
10
9
8
7
6
5
4
3
2
1
0
100
Insert
Insert
Closed
Saunders & Morgan
Open
Valente et al
Saunders & Morgan,
Insert
Valente et al, ER3A
Hawkins et al
Valente et al, TDH39
Supra-aural
Hawkins etal, TDH39
Valente et al
Hawkins et al, ER3A
1000
Frequency (Hz)
Hawkins etal
10000
Trainable Hearing Aids
30
Gain (dB)
25
20
CR
Gain
15
10
5
CT
0
30
40
50
60
70
Input level (dB SPL)
80
90
In summary…
In summary
How prevalent is mild hearing loss?
How common is hearing aid use amongst
those with mild hearing loss?
What are the characteristics of mild hearing loss?
Is mild hearing loss a problem to people?
very
not very
many, including spatial
hearing loss
yes, in noise
Do hearing aids help people with mild
hearing loss?
only in quiet places
Why don’t more people with mild hearing loss
even try hearing aids?
….. expected benefit
too small re need
How can hearing aids provide greater benefit
where it is most needed?
closed-ear, binaural
processing
Messages for ….
Public health authorities:
• Increase hearing awareness
(prevention, rehabilitation)
• Increase hearing screening
opportunities
Messages for ….
Clinicians:
• Discern primary reasons why
unmotivated clients are unmotivated
• Provide information to change
unrealistic beliefs
• Understand and diagnose the
fundamental problem that clients are
presenting with SRT loss
Messages for ….
Researchers:
• Better understanding of the components
and causes of SNR loss
• Prescription procedures for adaptive noise
suppression
• Time constants
• Relationship with thresholds
• Relationship with noise spectrum and
level
Messages for ….
Manufacturers:
• Achieve better performance in noise
 Binaural processing
 Closed fittings
 Wireless
 Smarter adaptive noise suppression
Hearing aids of the future
?

Convergence:
• hearing aid/enhancer,
• phone interface,
• hearing protector,
• computer interface (in and out),
• music player,
• GPS interface
Thanks for listening
For the slides from this talk ..…
www.nal.gov.au
Amplification and directivity
Aided
1/3 oct level at TM
(dB SPL)
Unaided
1/3 oct level at TM
(dB SPL)
50 dBA
80 dBA
100
100
80
80
60
60
40
40
20
100
20
100
1000
10000
100
100
80
80
60
60
40
40
20
100
20
100
1000
Frequency (Hz)
10000
1000
10000
1000
10000
Frequency (Hz)