1. 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

2. Slides on the NAL web site:

3. 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

4. 4FAHL or 3FAHL?

5. How prevalent is mild hearing loss?

6. 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

7. Blue Mountains 4FAHL better ear
Hartley et al (in press)

8. Aging population - Australia

9. Population aging, worldwide

10. Hearing loss distribution (3FAHL better ear)
BMHS population
OHS population

12. Mild losses for study ~ Minimum loss eligible for government benefits
Mild loss (4FA=29 dB)
Mild-mod loss (4FA=39 dB)
~ Median loss newly fitted in Australia

13. Mild losses for study 4FA HL Mild 9 dB Mild-mod 39 dB Moderate 49 dB
Mod-Sev dB
Severe dB

14. How common is hearing aid use amongst those with mild hearing loss?

15. Penetration by hearing loss
Penetration as a function of hearing loss
Davis (1995)
Wilson et al (1998)
Hartley et al (in Press)
Kochkin
consistent

16. Aid ownership by hearing loss Blue Mountains Population >55 years
Overall Use/Ownership =75% if include all use categories
Overall Use/Ownership =68% if include all use of more than 1 hr/week
Hartley et al (in Press)

17. What are the characteristics of mild hearing loss?

18. 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

19. Loss of active process in cochlear: OHC and OAE

20. Loss of frequency resolution
FRI f A f A
Ching & Dillon (unpublished data)

21. Frequency resolution

22. Loss of temporal resolution
TRI t

23. Temporal resolution
Ching & Dillon (unpublished data)

24. 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,

25. A digression into “normal” hearing

26. Spatial Processing Disorder
Noise
Noise
Speech
Sharon Cameron
Noise
Previous research at NAL has shown that a number of children with suspected APD have difficulty separating sounds that arrive simultaneously at the ears from different locations.
Tendency to affect children with history of COM.
Deficit likely related to ability to use binaural (ITD; IID) cues
Noise 26 26

27. Listening in Spatialised Noise - Sentences (LiSN-S) Conditions
Same voices
Different voices
Talker Advantage
Same
direction
Low Cue
Spatial Advantage
Total Advantage
Different
directions
High Cue
Cameron & Dillon (2009) 27

28. LiSN-S Diagnostic Screen

29. Spatial Advantage (≡ Spatial Release from Masking)
Nth America
Australia
Better
This graph shows performance on the spatial advantage measure.
Spatial advantage is calculated as the difference between the low-cue SRT and SV90 condition.
Adult like performance on the spatial advantage measure is achieved earlier than on talker advantage. Children are able to use ITD and IID as well as adults by about 11 years of age.
Again, there is no decline in spatial processing ability in older adults. 29

30. Spatial Advantage Better Control vs. LD: p = 0.983
Control vs. SusCAPD: p < *
SusCAPD vs. LD: p = *

31. Results profile: spatial processing disorder

32. Spatial processing remediation Pre vs. Post (n=9)
LC SRT p = 0.158
Talker Advantage - p = 0.981
HC SRT p =
Spatial Advantage - p =
Total Advantage - p = 0.001
Vertical bars denote 0.95 confidence intervals
F(8, 64)=5.3847, p=.00003 32

33. Application to people with hearing loss

34. Spatial hearing loss in hearing-impaired people: LiSN-S Prescribed Gain Amplifier

35. Deficit in SRTn with hearing loss
P =
Cameron, Glyde & Dillon, unpublished data)

36. Cause of deficit in SRTn
P =
Cameron, Glyde & Dillon, unpublished data)

37. Talker advantage deficit versus age
Cameron, Glyde & Dillon, unpublished data)

38. Binaural processing x x ~ Executive control CAPD ILD ITD CN
SO / IC / A1
ILD
ITD x L R ~
Sensorineural
hearing loss

39. 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

40. 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
1.8 dB / 10 dB
Carter, Zhou & Dillon, unpublished data)

41. Should mild hearing loss interfere with speech perception?

42. Speech and noise levels
SNR
Source: Pearsons, Bennett and Fidell (1977)

43. Calculation of SII
Noise = 60 dBA Speech = 64 dBA SIInh= SIIhi=0.46

44. Effective audibility 40 60 80
100 20

45. Transfer function SII  Percent correct

46. Mild losses for study
Mild loss (4FA=29 dB)
Mild-mod loss (4FA=39 dB)

47. Predicted speech intelligibility
Greatest problems in noisy places !!

48. Predicted variation of SRTn with hearing loss
Modified SII model predicts only 0.4 dB loss per 10 dB of hearing loss
Speech
level

49. 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

50. Calculation of intelligibility
Speech spectrum
Sensation Level
Effective audibility
Noise spectrum
SII
(Information received)
Percent correct
Max
Importance function
Threshold

51. Do hearing aids help people with mild hearing loss?
current ^
Do hearing aids help people with mild hearing loss?

52. Benefit of hearing aids
Predict increase in speech intelligibility
with
the modified Speech Intelligibility Index

53. Calculation of aided benefit
Noise = 50 dBA
Speech = 58 dBA

54. Speech intelligibility (mild loss)
Hearing aid “helps” in quiet places
Tiny additional benefit from directivity
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB

55. Speech intelligibility (mild-moderate loss)
Hearing aid “helps” in quiet places
Tiny additional benefit from directivity
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -5.1 dB

56. Speech intelligibility (moderate loss)
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -6.5 dB

57. Speech intelligibility (moderate-severe loss)
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -7.7 dB

58. Speech intelligibility (severe loss)
Conditions:
DI = 3 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR loss re n.h. = -9 dB

59. Summary of benefit versus HL
Background noise level
40 dB A
60 dB A
80 dB A

60. Why don’t directional microphones help more in noise?
(and adaptive noise reduction)

61. 1. Impact of open fittings on directivity
Omni-directional
Directional
DI = 3 dB  1.5 dB
DI = 10 dB  5 dB

62. Frequency range of directional mic (mild loss)
Effect of dynamic noise reduction on directional mic 50 60 70 80

63. Effect of aiding at 60 dBA (mild loss)
Noise = 60 dBA
Speech = 64 dBA

64. Effect of aiding at 80 dBA (mild loss)
Noise = 80 dBA
Speech = 76 dBA

65. 2. Impact of reverberation on directivity (and vice versa)
Total
Reverberant
Direct

66. Impact of reverberation on directivity (and vice versa)
Total
Direct
Reverberant

67. 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!!)

68. Conclusion of acoustic analysis
People with mild loss need help in noisy places
Hearing aids increase the speech information available mostly in quiet places!
Mics directional only where there is gain
high frequencies and lower levels
Where audibility is limited by threshold, not noise

69. So, objective benefit questionable, and increasing with degree of loss, but …….
What do hearing aid users say ?

70. Experimental evaluation of self-reported 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%)

71. Hearing loss distribution
Sample distribution
Overall Use/Ownership =75% if include all use categories
Overall Use/Ownership =68% if include all use of more than 1 hr/week
Population distribution

72. Usage of hearing aids

73. Factor analysis of questionnaire
Factor Loadings
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
-0.00
Q7: Residual handicap
-0.29
-0.56
-0.06
Q8: Bother to others
-0.68
-0.26
Q9: Quality of life
0.02
Q10: Replace them
0.34
-0.15
-0.23
Q11: Face vision
-0.42
Q12: paper vision
-0.22
-0.47
Proportion of variance
0.32 20
0.12
International Outcomes Inventory
for
Hearing Aids
Composite benefit
Composite difficulty
Vision

74. Effect of hearing loss on benefit

75. If hearing loss does not determine benefit, then what does?

76. Wishes And Needs Tool How strongly did you want to get hearing aids?
 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

77. Difficulty hearing unaided and wish to get hearing aids
Want hearing aids
Very much
Not at all
Unaided difficulty related to wish to get hearing aids

78. Need increases with hearing loss

79. Benefit versus need strength

80. Why don’t more people with mild hearing loss even try hearing aids?

81. 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 ….

82. 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

83. Health Belief Model
People act rationally, in their best interests, based on their beliefs
Weighing up of beliefs for and against a health decision
Do I have
a problem?
Is it serious
enough for me to
want to remove it?
Is there a
solution
that works?
Disadvantages
Advantages
What are the
disadvantages
of the solution?
“My hearing loss is not bad enough to need them” (Kochkin, 1993)

84. Motivation comes from ….
Try them
Self-image
Expect benefit
Expect to manage them
$ Cost OK
Acknowledge loss
Experience difficulty
Experience handicap

85. Difficulties experienced: frequency, severity
Health belief model
Difficulties experienced: frequency, severity
Self-image
External
image
Hearing aid
effectiveness
Ability to
manage
Cost
Incon-venience
Hearing
loss

86. Difficulties experienced: frequency, severity
Health belief model
Hearing
loss
Cost
Difficulties experienced: frequency, severity
Self-image
Ability to
manage
Hearing aid
effectiveness
External
image
Inconven-ience

87. Difficulties experienced: frequency, severity
Health belief model
Hearing
loss
Cost
Difficulties experienced: frequency, severity
Self-image
Ability to
manage
Hearing aid
effectiveness
External
image
Inconven-ience

88. How can the balance of benefits to disadvantages be improved?

89. Improving advantages and removing disadvantages
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
Problem 1
Solution 1
Problem 2
Solution 2
Problem 3
Solution 3
Cost
Working better
in noise

90. Speech intelligibility in noise

91. Binaural-Processing Super-directional Microphone (Mejia et al., 2007)Q1 Q2 Q3 Q4 ∑
Binaural beamformer
Main directional signal W3 W4 ∑
Rout K W1 W2 ∑
Lout K
Subsidiary signal
Rear- directional array
Masking threshold
Cross-fading process
Outputs with spatial reconstruction
HRTFL
HRTFR
Z-d
d = 3 ms delay
(Precedence effect)
DOA- reconstruction

92. Super-directional microphones

93. Speech reception threshold in noise Reverberant room: crit dist = 0
Speech reception threshold in noise Reverberant room: crit dist = 0.4m, radius = 1 m
Mejia and Johnson, unpublished data

94. Linked binaural hearing aid technology
Female
talker
Male
talker
Listener
Children
playing
Hearing Aid 94 94

95. 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.

96. Effect of super-directivity (mild loss)
Super-directional mic not directional at all over a broader and broader range as noise levels rise
Conditions:
DI = 6 dB when REIG > 3 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB

97. So super-directivity alone is no use ……..

98. What if we could achieve directivity at low frequencies?

99. Effect of low-frequency directivity (mild loss)
Now directional over entire frequency range in noisy places
Conditions:
DI = 3 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB

100. Occlusion with closed molds
Vent or leak transmission in

101. Active Occlusion Reduction
Hear
Aid C Σ + - A B

102. Active occlusion reduction
Mejia, Dillon, & Fisher (2008)

103. Active occlusion reduction
In combination?
Active occlusion reduction
(closed mold)
Super-directivity +
= ?

104. Low-frequency super-directivity (mild loss)
Super-directivity over entire frequency range
 super-normal hearing
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -3.7 dB

105. Low-frequency super-directivity (mild-moderate loss)
Super-normal hearing for the median hearing aid wearer
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -5.1 dB

106. Low-frequency super-directivity (moderate loss, 4FA = 49.8 dB HL)
Super-normal hearing in very noisy places for even a moderate-severe loss
Conditions:
DI = 6 dB when REIG ≥ 0 dB
n.h. spatial adv = 6 dB
∆SNR re n.h. = -6.5 dB

107. 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

108. Cost
Jump to summary

109. Self-fitting hearing aid
Automatic
Real-ear to coupler difference
Adjust Hearing Aid
NAL-NL2 Prescription Formula
Audiometer
Plus trainability
Australia, USA: 1 audiologist per 10,000 people
Developing countries: 1 audiologist per 500,000 people, to 1 per 6,000,000

110. Automatic versus manual audiometry
1 kHz

111. Test-retest standard deviations
Manual audiometry (5 dB Hughson-Westlake)
NAL-NL2
RECD
Adjust
Auto Aud
Automatic audiometry (2 dB final step size)

112. Real-Ear to Dial Difference: Inter-subject standard deviations

113. Real-Ear to Dial Difference: Inter-subject standard deviations
Insert
Saunders & Morgan
Valente et al
Hawkins et al
Supra-aural
Hawkins etal

114. Trainable Hearing Aids
Gain CT CR

115. In summary…

116. In summary How prevalent is mild hearing loss? very
How common is hearing aid use amongst those with mild hearing loss?
not very
many, including spatial hearing loss
What are the characteristics of mild hearing loss?
Is mild hearing loss a problem to people?
yes, in noise
Do hearing aids help people with mild hearing loss?
only in quiet places
….. expected benefit too small re need
Why don’t more people with mild hearing loss even try hearing aids?
How can hearing aids provide greater benefit where it is most needed?
closed-ear, binaural processing

117. Messages for …. Public health authorities:
Increase hearing awareness (prevention, rehabilitation)
Increase hearing screening opportunities

118. 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

119. 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

120. Messages for …. Manufacturers: Achieve better performance in noise
 Binaural processing
 Closed fittings
 Wireless
 Smarter adaptive noise suppression

121. Hearing aids of the future? 
Convergence:
hearing aid/enhancer,
phone interface,
hearing protector,
computer interface (in and out),
music player,
GPS interface

122. For the slides from this talk ..… www.nal.gov.au
Thanks for listening
For the slides from this talk ..…

123. Amplification and directivity
50 dBA
80 dBA
Unaided
Assumptions: 3 dB DI for REIG > 5 dB
3 dB spatial advantage and -3 dB spatial loss
Aided