A brief history of hearing aids

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

 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?

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

 1940 Selective amplification
formula
 1946 Harvard Report

 1958 Shore, Bilger, Hirsch –
couldn’t differentiate
hearing aids using clinical
speech recognition
measures*

 Probe microphone measures where
more than 25 years away…

 1968 directional
microphones*

 Just starting to focus on difficulty
hearing in noise…

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

 1975 compression –
starting to be
automatic*

 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…

 1978 – audiologists
dispense hearing aids
(legally)

 1979 Skinner –
audibility, bandwidth,
and comfort*

 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…

 1985 DSL 3.0; 1986 NAL-R
 1985 Probe Microphone
Measurement Equipment
 1985 wide dynamic range
compression implemented*

Past = linear hearing
aids and volume
controls were
mandatory.
Present = compression
signal processing, now
volume controls are
used as a manual over-
ride.

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…

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.

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.

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

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

 1990 Valid, reliable
self-evaluation
measures (Cox et al;
Gatehouse et al)*

 Individual solutions
 Outcome assessment

 1993 IHAFF calls for
three dimensional
hearing aid fitting
targets*

 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.

 1994 Soli et al –
Hearing in Noise
testing*

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

 1995 first custom
digital product*

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

 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)?

 10 years after the introduction of 3
dimensional hearing aid fittings, we
have targets for the hearing aids…

 1996 Noise reduction
algorithms*

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
Noise Noise Noise Noise Noise
SignalSignalSignal Noise NoiseNoise
SignalSignal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal
SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise 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.

From Boothroyd
OUTPUT
Frequency
Looks like? Mostly Mostly Mostly Mostly Mostly Mostly Mostly Mostly
S S N S N S S N
INPUT SignalSignal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise
SignalSignal
SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal
SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise 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.

 1997 directional/
omnidirectional choice*

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

 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.

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

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

Dead Regions: Typical Audiogram
Frequency

 2002
automatic/adaptive
directionality*

 How smart can the hearing aid be?
 How smart do we want it to be?

 2002 adaptive
feedback control*

 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.

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

 2002 Scollie/probe mic
signals

 2003 Stelmachowicz-
bandwidth for children
learning speech*

 This is the same message that
Skinner et al was providing in
1979…still not there…

 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

 2004 customizing
features/hiding
features

 2005 feedback
management
systems/open
fit/drastic increase in
channels*

Open fit KEMAR comparisons
0
1
2
3
4
5
6
7
8
250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 6300 8000
Hz
delay(ms)
Open mold
Closed

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)

 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.

 2005 Surge of evidence
based practice
guidelines (IHAFF)*

 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.

 2005 Expansion as a
programmable feature*

 We conquered audibility only to
hear patients saying that they were
hearing too much…

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.

 2006 wireless
communication
between hearing aids*

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?

 2006 rechargeable
batteries*

 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.

 2006 built-in FM
receiver in several
levels of technology*

A step in the right direction…
 One less extra piece of equipment
 The solution is specific to the
transmitter

 2006 Acceptable Noise
Level Test as a
predictor*

Interesting prediction data; may give
noise reduction new life…

 2006 Mueller and
Ricketts – 10 things to
know about open
fittings

 2007 FCC ruling on cell
phone compatibility

 2007 DSL(i/o)v.5; NAL-
NL2

 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

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

The world of sound… interfaces
 Personal communication
 Cell phones
 Personal listening devices
 Computers
 Television
 Airplanes

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

A brief history of hearing aids

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A brief history of hearing aids