1. A Brief History of Hearing Aids
Catherine Palmer, PhD
Associate Professor, University of Pittsburgh
Director, Audiology and Hearing Aids,
University of Pittsburgh Medical Center
palmercv@upmc.edu
2. What have the important newsflashes in
audiology and technology been over time?
How have these events impacted where
we are today?
Where are we headed?
What are the next challenges?
3. Time Line: 1800’s to 1969
1800 F.C. Rein (first
company)
1819 Acoustic Throne,
King John Portugal
1850s Politzer – ear
trumpet
1876 Bell invented the
telephone
1900 Dr. Ferdinand Alt –
1st
electronic hearing aid
1906 DeFrost – vacuum
tube (great amplification)
1921 – Earl Hansen
patented the vacuum tube
hearing aid
1930 2 part instrument
1937 1st
wearable hearing
aid
1940 Selective amplification
formula
1946 Harvard Report
1947 Transistor
1952 Transistor in hearing
aids
1954 Eyeglass hearing aids
1958 Shore, Bilger, Hirsch –
couldn’t differentiate
hearing aids using clinical
speech recognition
measures
1960 hearing aid could be
all on one side
1968 directional
microphones
9. Time Line: 1970’s - 1980’s
1970 custom products
1975 compression –
starting to be automatic
1976 Pascoe’s study of
bandwidth
1978 – audiologists
dispense hearing aids
(legally)
1979 Skinner –audibility,
bandwidth, and comfort
1980 Schwartz and
Walden – identified the
problem in testing as
word recognition being
unreliable
1981 Studebaker – 845
words to determine a
4% significant difference
in word recognition
mid-1980s 1st
digital (two
pieces)
1985 DSL 3.0; 1986 NAL-R
1985 Probe Microphone
Measurement Equipment
1985 Wide dynamic range
compression implemented
1987 Programmable
12. It wouldn’t be until 1985 that we
would see true wide dynamic range
compression and the ability to
automatically make soft, average,
and loud sound audible for an
individual…
13. 1978 – audiologists
dispense hearing aids
(legally)
15. Bandwidth continues to be
inadequate for children learning
speech and for anyone enjoying
music. The advent of digital
hearing aids and the interest in
dead regions has actually made this
worse…
17. Past = linear hearing
aids and volume
controls were
mandatory.
Present = compression
signal processing, now
volume controls are
used as a manual over-
ride.
18. 1985 was a big year…
We finally have research based
fitting targets and equipment that
can make appropriate
measurements, but the technology
has outpaced the targets. WDRC
requires three targets (soft,
moderate, and loud) to be fit
appropriately…
19. An incredibly powerful tool for the clinician. No patient should
leave a hearing aid fitting without the clinician knowing what
SPL is reaching the eardrum and without a clear understanding
of the audibility that has been restored across input levels.
20. Insertion Gain Figure from Hawkins & Cook
(2003)
0.25 0.5 2 3 4 61
-25
-20
-15
-10
-5
0
5
10
Frequency (kHz)
ActualIGMinus
SimulatedIG(dB)
Negative values indicate that the actual insertion gain was
less than the simulated insertion gain.
22. Kochkin’s surveys indicate that the use of
programmable hearing aids improves consumer
satisfaction…
WDRC implemented
Two channels fairly standard
Class B or D receivers standard
Output compression limiting
standard
23. Time Line: 1990’s
1990 Valid, reliable
self-evaluation
measures (Cox et al;
Gatehouse et al)
1993 IHAFF calls for
three dimensional
hearing aid fitting
targets
1994 Soli et al –
Hearing in Noise
testing
1995 first custom
digital product
1995 DSL i/o
1996 Noise reduction
algorithms
1997 directional/
omnidirectional choice
1998 RECD
1999 NAL-NL1
24. 1990 Valid, reliable
self-evaluation
measures (Cox et al;
Gatehouse et al)*
26. 1993 IHAFF calls for
three dimensional
hearing aid fitting
targets*
27. This is almost ten years after the
technology arrived to provide 3
dimensional hearing aid fittings
(gain varies as a function of
frequency and input level). The
solution was still 3-6 years away.
29. SNR Loss
“Loss in ability to understand speech at the SNR
used by those with normal hearing”
Attributed to inner hair cell loss
•Killion M. (1997). SNR loss: “I can hearing what people say, but I can’t understand them”
Hearing Review 4(12):8, 10, 12, 14
31. Why Digital
distortion/sound Quality
fine tuning
programmable telecoil
turn VC off
automatic feedback control
automatic and/or adaptive directionality
organizing the order of programs
insitu measurements
seemingly infinite number of channels
endless possibilities for algorithms
changes in signal processing based on sampling the
incoming signal
32. The possibilities are unlimited
(limited by battery drain).
The question is what does the
impaired system need (you would
need to understand the impaired
system, speech acoustics, and the
environment in which one would like
to communicate)?
36. From Boothroyd
OUTPUT
Time
Looks like? Mostly Mostly Mostly Mostly Mostly Mostly Mostly Mostly
S S N S N S S N
INPUT SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
SignalSignalSignal Noise NoiseNoise
SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise Noise NoiseNoise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
SignalSignalSignal Noise NoiseNoise
SignalSignalSignal SignalSignalSignal Noise NoiseNoise
Figure 2. Time-domain noise-reduction algorithms introduce attenuation when the mixed
signal appears to consist mostly of noise.
37. From Boothroyd
OUTPUT
Frequency
Looks like? Mostly Mostly Mostly Mostly Mostly Mostly Mostly Mostly
S S N S N S S N
INPUT SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
SignalSignalSignal Noise NoiseNoise
SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal
Signal Signal Signal Signal Signal
SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise Noise NoiseNoise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
Signal Signal Signal Signal Signal
Noise Noise Noise Noise Noise
SignalSignalSignal Noise NoiseNoise
SignalSignalSignal SignalSignalSignal Noise NoiseNoise
Figure 3. Spectral-domain noise-reduction algorithms introduce attenuation in those frequency
regions where the mixed signals appears to consist mostly of noise.
39. User Satisfaction with Single (N=200)
and Directional Microphones (N=296)
re: Marketrak (N= 418)
• Kochkin S. (2000). Customer satisfaction with directional DSP
aids. Hearing Review 7(11):24, 26, 28-29, 32-34
41. Getting ready to handle hearing aid
fitting with infants that will come
with universal newborn screening.
RECD allows complete pre-setting of
the hearing aid without the need for
patient cooperation and/or input.
45. Time Line: 2000
2001 Dead Regions
2002 automatic/adaptive
directionality
2002 adaptive feedback
control
2002 Scollie/probe mic
signals
2003 Stelmachowicz-
bandwidth for children
learning speech
2003 Touchless Telecoil
2004 customizing
features/hiding features
2005 feedback management
systems/open fit/drastic
increase in channels
2005 Surge of evidence
based practice guidelines
(IHAFF)
2005 Expansion as a
programmable feature
2006 wireless
communication between
hearing aids
2006 rechargeable
batteries
2006 built-in FM receiver
in several levels of
technology
2006 Acceptable Noise
Level Test as a predictor
2006 Mueller and Ricketts
2007 FCC ruling on cell
phone compatibility
2007 DSL(i/o)v.5; NAL-
NL2
2007 wireless paradigm
shift
46. Why are patients not wearing their hearing aid(s)?
Kochkin S. (2000). MarketTrak V: “Why are my hearing aids in the
drawer?”: the consumer’s perspective. Hearing Journal 53(2): 34, 36,
39-42
Reason Percent Est. # of
Owners
Poor Benefit 29.86 268,510
Background
Noise
25.3 229,470
Fit/Comfort 18.7 169,448
Price/Cost of
Repair
10.3 93,848
52. It’s not an excuse for a poor hearing
aid fitting.
The hearing aid has to feed back in
order to engage the system – this
isn’t acceptable for some patients.
53. Satisfaction, Benefit & Value (Kochkin, 2002)
11
26
16
13
13
7
19
10
18
89
74
79
73
44
93
71
85
64
Usage
Wear HI
Wear HI 4+ hours
Behavioral
Recommend HI to friend
Recommend dispenser
Would repurchase H.I. brand
Quality of life improvement
Key Satisfaction Indices
Overall satisfaction
Benefit
Value
020406080100
% Dissatisfied
0 20 40 60 80 100
% Satisfied
58. Great idea, but it arrived just as cell
phones became the primary
telephone for many individuals…
By 2006 there would be 1 billion cell
phones in use
62. Spectrographs for the syllable /pa/
•(a) shows /pa/ with an Envelope Onset Asynchrony (EOA) of 26 ms (circled)
•EOA= the onset of low frequency energy – the onset of high frequency energy
•This EOA is the natural pattern of the syllable /pa/
•(b) shows /pa/ with an EOA of 1 ms
•The high frequency band was delayed to achieve this EOA pattern
•Although both tokens are utterances of /pa/, the high frequency delay caused
listeners’ perception to change from /pa/ to /ba/
a) b)
63. The algorithm manipulations
potentially are infinite, but we have
to look at what is happening to the
speech signal and what cues are
essential to the listener.
64. 2005 Surge of evidence
based practice
guidelines (IHAFF)*
65. Evidence-based medicine has
demoted the “medical expert” to the
least valid form of evidence and all
“experts” now are expected to be
able to reference their
pronouncements to the relevant
literature.
67. We conquered audibility only to
hear patients saying that they were
hearing too much…
68. Expansion provides
more gain as the
input increases (the
opposite of
compression). This
allows the clinician to
reduce very quiet
sounds that are
annoying the hearing
aid user. Expansion
has always been
used by
manufacturers to
reduce microphone
noise.
70. Why do the hearing aids need to
communicate?
True binaural processing? By 2005, 86%
of fittings were binaural.
Is phase an important cue?
Is it important to have the hearing aids
set in the same listening condition (e.g.,
both in directional?)
Will this help people localize?
Is it just more convenient (e.g., VC)?
Is it inconvenient when there is a repair?
72. Very little has happened over time
in terms of battery development.
Batteries continue to be a limiting
factor in signal processing and in
patient frustration.
73. 2006 built-in FM
receiver in several
levels of technology*
74. A step in the right direction…
One less extra piece of equipment
The solution is specific to the
transmitter
81. A paradigm shift
Communicating between
the hearing aids and the programmer,
between the two hearing aids, and
between your patient and the world
Seamless interfaces
82. The impaired system…
Threshold
elevation
Loudness
Recruitment
Reduced
Frequency
Selectivity
Reduced Temporal
Discrimination
Hard to hear in
quiet
Hard to be
comfortable
Hard to hear in
noise
Hard to hear in
noise and real
rooms
83. The world of sound… interfaces
Personal communication
Cell phones
Personal listening devices
Computers
Television
Airplanes
84. Challenges for the clinician
Measure SPL at the eardrum
Choose a valid, reliable outcome measure
Remember: feedback, occlusion problems, and
loudness comfort are still the top three reasons for
individuals rejecting hearing aids
Batteries and moisture continue to be a problem for
patients
Re-structure your time so customization is part of
your activities
Embrace new developments while following an
evidence based approach
Provide the rehabilitation that makes the person an
active participant
Include hearing protection in everything you do