A brief history of hearing aids

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A brief history of hearing aids

  1. 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. 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. 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
  4. 4.  1940 Selective amplification formula  1946 Harvard Report
  5. 5.  1958 Shore, Bilger, Hirsch – couldn’t differentiate hearing aids using clinical speech recognition measures*
  6. 6.  Probe microphone measures where more than 25 years away…
  7. 7.  1968 directional microphones*
  8. 8.  Just starting to focus on difficulty hearing in noise…
  9. 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
  10. 10.  1970 custom products
  11. 11.  1975 compression – starting to be automatic*
  12. 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. 13.  1978 – audiologists dispense hearing aids (legally)
  14. 14.  1979 Skinner – audibility, bandwidth, and comfort*
  15. 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…
  16. 16.  1985 DSL 3.0; 1986 NAL-R  1985 Probe Microphone Measurement Equipment  1985 wide dynamic range compression implemented*
  17. 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. 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. 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. 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.
  21. 21.  1987 Programmable*
  22. 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. 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. 24.  1990 Valid, reliable self-evaluation measures (Cox et al; Gatehouse et al)*
  25. 25.  Individual solutions  Outcome assessment
  26. 26.  1993 IHAFF calls for three dimensional hearing aid fitting targets*
  27. 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.
  28. 28.  1994 Soli et al – Hearing in Noise testing*
  29. 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
  30. 30.  1995 first custom digital product*
  31. 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. 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)?
  33. 33.  1995 DSL i/o*
  34. 34.  10 years after the introduction of 3 dimensional hearing aid fittings, we have targets for the hearing aids…
  35. 35.  1996 Noise reduction algorithms*
  36. 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. 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.
  38. 38.  1997 directional/ omnidirectional choice*
  39. 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
  40. 40.  1998 RECD*
  41. 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.
  42. 42. EPR 4 y/o MPM 5 y/o GPR 1 y/o
  43. 43.  1999 NAL-NL1
  44. 44. 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
  45. 45. 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
  46. 46.  2001 Dead Regions*
  47. 47. Dead Regions: Typical Audiogram Frequency
  48. 48.  2002 automatic/adaptive directionality*
  49. 49.  How smart can the hearing aid be?  How smart do we want it to be?
  50. 50.  2002 adaptive feedback control*
  51. 51.  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.
  52. 52. 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
  53. 53.  2002 Scollie/probe mic signals
  54. 54.  2003 Stelmachowicz- bandwidth for children learning speech*
  55. 55.  This is the same message that Skinner et al was providing in 1979…still not there…
  56. 56.  2003 Touchless Telecoil*
  57. 57.  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
  58. 58.  2004 customizing features/hiding features
  59. 59.  2005 feedback management systems/open fit/drastic increase in channels*
  60. 60. 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
  61. 61. 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)
  62. 62.  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.
  63. 63.  2005 Surge of evidence based practice guidelines (IHAFF)*
  64. 64.  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.
  65. 65.  2005 Expansion as a programmable feature*
  66. 66.  We conquered audibility only to hear patients saying that they were hearing too much…
  67. 67. 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.
  68. 68.  2006 wireless communication between hearing aids*
  69. 69. 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?
  70. 70.  2006 rechargeable batteries*
  71. 71.  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.
  72. 72.  2006 built-in FM receiver in several levels of technology*
  73. 73. A step in the right direction…  One less extra piece of equipment  The solution is specific to the transmitter
  74. 74.  2006 Acceptable Noise Level Test as a predictor*
  75. 75. Interesting prediction data; may give noise reduction new life…
  76. 76.  2006 Mueller and Ricketts – 10 things to know about open fittings
  77. 77.  2007 FCC ruling on cell phone compatibility
  78. 78.  2007 DSL(i/o)v.5; NAL- NL2
  79. 79.  2007 Wireless interfaces*
  80. 80.  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
  81. 81. 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
  82. 82. The world of sound… interfaces  Personal communication  Cell phones  Personal listening devices  Computers  Television  Airplanes
  83. 83. 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

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