A brief history of hearing aids

A Brief History of Hearing Aids

Catherine Palmer, PhDAssociate Professor, University of Pittsburgh

Director, Audiology and Hearing Aids, University of Pittsburgh Medical Center

[email protected]

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

1970 custom products

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 = compressionsignal processing, nowvolume 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)

Ac

tua

l IG

Min

us

S

imu

late

d I

G (

dB

)

Negative values indicate that the actual insertion gain was less than the simulated insertion gain.

1987 Programmable*

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)?

1995 DSL i/o*

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 MostlyS S N S N S S N

INPUTSignalSignal

Signal Signal Signal Signal Signal

SignalNoise Noise Noise Noise Noise Noise NoiseNoise


Noise Noise Noise Noise NoiseSignalSignalSignal Noise NoiseNoise

SignalSignal


SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal


SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise Noise NoiseNoise


Noise Noise Noise Noise Noise


Noise Noise Noise Noise NoiseSignalSignalSignal 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 MostlyS S N S N S S N

INPUTSignalSignal


SignalNoise Noise Noise Noise Noise Noise NoiseNoise


Noise Noise Noise Noise NoiseSignalSignalSignal Noise NoiseNoise

SignalSignal


SignalNoise Noise Noise Noise Noise Noise NoiseNoise SignalSignal


SignalNoise Noise Noise Noise Noise Noise NoiseNoiseNoise Noise Noise Noise Noise Noise NoiseNoise


Noise Noise Noise Noise Noise


Noise Noise Noise Noise NoiseSignalSignalSignal 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

1998 RECD*

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.

EPR 4 y/o

MPM 5 y/o

GPR 1 y/o

1999 NAL-NL1

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

2001 Dead Regions*

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…

2003 Touchless Telecoil*

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

del

ay (

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

2007 Wireless interfaces*

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

Education

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