Physics Colloquium
- 1. 1 Bionic Hearing: The Science and the Experience Ian Shipsey
- 2. 2 The physiology of natural hearing Causes of Deafness (30 million Americans cannot hear well) Solutions for hearing loss: The cochlear implant. Political & social issues The future of cochlear implants TALK OUTLINE
- 3. 3 The Outer Ear The videos shown in this talk are based on “Auditory Transduction” by Brandon Pletcsh which was awarded 1st place in the NSF/AAAS Science and Engineering Visualization Challenge 2003. Video edited by S. Lichti and I.S.
- 5. 5 1543 Anatomist Andreas Vesalius describes the structure of the middle ear. The tympanic membrane & ossicles
- 6. 6 The tympanic membrane & ossicles Through the ossicles the vibration of the tympanic membrane is transmitted to the stapes
- 7. 7 Bony Labyrinth stapes and round window
- 8. 8 The bony labyrinth, cochlea and it chambers 1561 Gabriello Fallopio discovers the snail-shaped cochlea of the inner ear. The cochlea is about the size of a pea
- 9. 9 The Cochlea houses the Organ of Corti Auditory Nerve
- 10. 10 Organ of Corti 1st detailed study of Organ of Corti by Alfonso Corti Original figures (scanned) from: Zeitschrift für wissenschaftliche Zoologie (1851) Hair Cells are a mechano-electric transducer
- 11. 11 The Basilar Membrane is a Frequency Analyzer
- 13. 13 Georg von Békésy (Nobel 1961) Hermann Ludwig von Helmholtz first theory of the role of BM as a frequency analyzer. base apex Experimentally measured basilar membrane displacements in cadavers. Very loud sounds were used to render the displacements visible displacement
- 14. 14 displacement Von Békésy (model) Modern measurement Live animal Response to 10KHz tone at low sound level 20 nm 0 nm (mm) Response to 20KHz tone at low sound level Von Békésy's findings in human cadavers stimulated the production of numerous mechanical cochlear models that reproduced the observed broad wave shapes. Much of the basilar membrane is displaced by each wave, and there is very large overlap between wave shapes for large differences in stimulus frequency These models predict the human has poor frequency selectivity poor perception of pitch. This is in contrast with psychophysical data on the excellent frequency selectivity of the human cochlea.
- 15. 15 There exists an amplifier within the organ of Corti that increases the displacement of the basilar membrane and provides excellent frequency selectivity ( i.e. excellent perception of pitch) (this amplifier is like the child on the swing) displacement Von Békésy (model) Modern measurement Live animal Response to 10KHz tone at low sound level 20 nm 0 nm (mm) Von Békésy's findings in human cadavers stimulated the production of numerous mechanical cochlear models that reproduced the observed broad wave shapes. Much of the basilar membrane is displaced by each wave, and there is very large overlap between wave shapes for large differences in stimulus frequency These models predict the human cochlea is poorly tuned (i.e frequency selectivity is poor poor perception of pitch.) This is in contrast with psychophysical data on the excellent frequency selectivity of the human cochlea.
- 16. 16 Active amplification Sensitive modern measurements on living animal cochlea Johnstone et al (1986) What causes the amplification? Expectation from von Békésy soft loud Same animal post mortem, amplification (and fine tuning) are gone
- 17. 17 Per cochlea: Inner hair cells 3,500 afferent (signals go the brain) Outer Hair Cells 12,500 Sparsely innervated Rows of Hair Cells in the healthy cochlea Hair cell 30m 5m Hair
- 18. 18 Hair cells are mechano-electrical transducers Both inner and outer hair cells work this way 500 nm <10nm diameter 1980’s
- 19. 19 The inner hair cells send signals to the brain that are interpreted as sound. What do the outer hair cells do? Outer hair cells exhibit electro motility they are also electro-mechanical transducers and are the amplifier 1987-2003
- 20. 20 The Five Main Causes of Hearing Loss 1. Heredity. 2. Infections, (ex: bacterial meningitis, rubella). 3. Acute or chronic exposure to loud sounds. 4. Prescription drugs, such as ototoxic antibiotics (streptomycin and tobramycin) and chemotherapeutic agents, such as cisplatin. 5. Presbycusis, the hearing loss of old age, Me in 1989 All of us 30 million Americans cannot hear well
- 21. 21 Conductive (the ossicles no longer function) 70% of hearing loss is sensorineural (loss of hair cells) (a) vast majority of cases involve loss of some hair cells (mild, moderate hearing loss) hearing aids (b) (4%) Loss of large numbers of hair cells Hearing aids do not help: no matter how loud the amplified sound the transduction mechanism (i.e. hair cells) are absent and so no electrical signals are produced and sent to the brain Cochlea Implant (CI) The main types of hearing loss
- 22. 22 Volta placed two metallic probes in both ears and connected the end of two probes to a 50- volt battery, and observed that: "... at the moment when the circuit was completed, I received a shock in the head, and some moments after I began to hear a sound, or rather noise in the ears, which I cannot well define: it was a kind of crackling with shocks, as if some paste or tenacious matter had been boiling... The first cochlea implant (1800)…. The disagreeable sensation, which I believe might be dangerous because of the shock in the brain, prevented me from repeating this experiment..." Alessandro Volta, Philosophical Transactions, Vol. 90 (1800), Part 2, pp. 403-431.
- 23. 23 1. Sounds are picked up by a microphone & turned into an electrical signal. 2. The signal passes to a speech processor (ASIC) where the spectrum is analyzed and “coded” (turned into a special digital pattern of electrical pulses). 3. These pulses are sent to a coil antenna, then transmitted across the intact skin (by radio waves) to a receiver in the implant. 4. The implant (ASIC) reads the program (data) and follows the instructions sending a pattern of analog electrical pulses to multiple electrodes in the cochlea. 5. The auditory nerve picks up the electrical pulses and sends them to the brain. 6. The brain recognizes the signals as sound. Unlike hearing aids, which make sounds louder, a Cochlear Implant bypasses the non-functional hair cells of the ear and delivers weak electrical signals directly to the auditory nerve. The Modern Cochlea Implant
- 24. 24 timeamplitude High frequency low frequency High f Low f cochlea base cochlea apex In natural hearing high frequency sound stimulates the cochlea and auditory nerve at the base, low frequency sound at the apex. The key idea: the cochlea implant exploits the natural arrangement of the cochlea & auditory nerve by using 10-22 electrodes each placed at a separate location in the cochlea. The speech processor continuously measures and sorts the sound signal by pitch and loudness. High frequency sounds are sent to electrodes at the cochlea base Low frequency sounds are sent to electrodes at the cochlea apex
- 25. 25 18,800 pulses per second white represents a pulsed electrode cochlea electrode auditory nerve
- 26. F0F2 F0F1F2 SPEAK CA CIS CA/CIS CIS Single- Channel Multipeak 0 10 20 30 40 50 60 70 80 90 100SentenceRecognition(%correct 3M House 1980 Nucleus WSP 1982 Nucleus WSP II 1985 Nucleus MSP 1989 Nucleus Spectra 22 1994 Ineraid MIT 1992 Ineraid RTI 1993 Clarion ABC 1996 MedEL Combi 1996 Cochlea implants have improved dramatically in twenty years 1 electrode multi- electrodes speech coding strategies Time Manu- facturer
- 27. 27 Who can have a Cochlear Implant? • Requirements for Adults (I’ll discuss children separately) – 18 years old and older (no limitation by age) – Bilateral moderate-to-profound sensori-neural hearing loss (with little or no benefit from state of the art hearing aids in a 6 month trial) ~1 million citizens now qualify but only ~37,000 CI’s in U.S. ( 23k Adults, 16K children: FDA 2006) – Psychologically suitable – No anatomic or medical contraindications If the requirements are met: Extensive audiological and medical testing, CT Scan/MRI, Patient chooses device: 3 major manufacturers of state of the art multi channel implants: Cochlear (Australia), MEDEL (Austria), Clarion (U.S.). All devices have similar performance the patient is the largest variable in the outcome • Wait for surgery (can be many months….) • Finally surgery day arrives
- 28. 28 Surgical Technique Surgery 2-4 hrs under general anesthesia
- 29. 29 Postoperative Management • Complication rate <5% • Wound infection/breakdown • Facial nerve injury • Vertigo • Device failure—re-implantation usually successful • Avoid MRI • Wait ~8 weeks for wound to heal before activation day Porter & Gadre (Galveston, TX) While waiting wonder how to pay the medical bill
- 30. 30 The cost of a CI: Insurance Issues A CI costs ~$60,000 including evaluation, surgery, post operative hospital care, extensive audiological (re)habilitation. Medicare/Medicaid pays total/partial cost. Some private insurers refuse to cover the devices, others provide excellent coverage. “The reimbursement levels have forced eight hospital to close CI programs due to the cost of subsidizing the implants.” (B. March President Cochlear America) Other hospitals ration services by putting children on waiting lists Currently~ 45,000 US children are CI eligible but only 15,000 have a CI (FDA, 2006) And yet the cost of CI is small compared to the cost in government aid for education and training estimated at $1 million over the course of a lifetime (not to mention the massive human cost). “Ultimately this is about the way society views hearing. Being deaf is not going to kill you and so the insurance companies do not view this as necessary.” D. Sorkin, VP Consumer Affairs, Cochlear Corp. (A manufacturer).“ I was one of the lucky ones the cost of my implant was fully covered by insurance. Fortunately, the insurance situation has improved considerably in the last several years. Activation day….
- 31. 31 How well does it work? My experience BEFOREPre-op 6 months after activation Normal 125 Hz 8000 Hz Frequency 0 soft 100 loud dB Speech pre-op 6 months Tests My test scores are no longer exceptional. 75% of recent postlingually deaf patients with state of the art devices can use the phone. Why does the CI work so well 3,500 inner hair cells 10 electrodes?
- 32. 32 Perception (visual or auditory) is a dynamic combination of top-down and bottom-up processing • The need for sensory detail depends on the distinctiveness of the object and the level of familiarity Visual examples… Hearing doesn’t end at the cochlea “If you see a huge gray animal in the distance you don’t need much detail to know that it is an elephant”
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- 44. 44 “CHOICE” SPECTROGRAPH ELECTRODOGRAPH (SPEAK STRATEGY)) TIME TIME ELECTRODE FREQUENCY (0-5KHz) Intensity of the sound is color coded, white is loudest Images courtesy of M. Svirsky, Indiana
- 45. 45 Optimizing Cochlear Implants to maximize speech recognition •What features of the pattern of neural output from the cochlea are most critical? Amplitude? Temporal? (pulse rate of the implant) Number of locations at which auditory nerve is stimulated Place of stimulation frequency
- 46. 46 1-channel1-channel 2-channel2-channel 4-channel4-channel 8-channel8-channel 16-channel16-channel OriginalOriginal Spectral Resolution (Number of Channels) Study Implant simulations by Arthur Boothroyd, based on the work of Robert Shannon Like Volta
- 47. 47 Most important factor for speech recognition is the number of spectral channels of information Spectral Resolution (Number of Channels) Study % Correct Number of channels
- 48. 48 0 10 20 30 40 50 60 70 80 90 100 PercentCorrect PREOP 2 1 3 6 WEEKS MONTH MONTHS MONTHS N = 67 It takes time to adjust to the limited sensory detail provided by the cochlear implant, i.e. to learn how to understand speech with a cochlear implant The adult brain is quite plastic The CI Learning Curve Time % All of the adults in this study were post lingually deaf (they had the advantage of being able to use top down processing to understand speech.) What about prelingually deaf children?
- 49. 49 The Deaf Community and Cochlear Implants • People can lead full and satisfying lives without emphasizing speech when they are part of the Deaf community (learning English is important, learning speech is less so.) • In the 1990s strong opposition to pediatric implants while generally neutral towards adult implantation. • An implant will delay a deaf child’s acquisition of sign language (a deaf child’s “natural language”) and assimilation into the deaf community. • 1991 position statement National Association of the Deaf: “deplores the FDA decision to approve pediatric implantation as being unsound scientifically, procedurally, and ethically.” • Today, the deaf community tends to regard cochlear implantation as a personal decision. 2000 position statement (www.nad.org): – Emphasizes taking advantage of technological advancements that have the potential to improve the quality of life for deaf and hard of hearing persons, and “strongly supports the development of the whole child and of language and literacy.”
- 50. 50 Language Development in Profoundly Deaf Children With Cochlear Implants (Svirsky, Miyamoto et al. Indiana U.) AGE (months) 0 24 48 72 96 LANGUAGEAGE(months) 0 24 48 72 96 Figure 1 CHRONOLOGICAL AGE (months) 0 12 24 36 48 60 LANGUAGEAGE(months) 0 12 24 36 48 60 N=23 Figure 2 Without CI (predicted) With CI “Despite a large amount of individual variability, the best performers in the implanted group seem to be developing an oral linguistic system based largely on auditory input from a cochlear implant” HEARING DEAF To be implanted Before & at 3 intervals after implantation
- 51. 51 Original Music through a CI Due, in part, to a small number of electrodes, the CI user has poor pitch resolution. In most cases, this does not hinder speech comprehension but music appreciation relies on the ability to recognize pitch Melody recognition is extremely difficult (lyrics help) Cochlear Implants and Music (These two musical demonstrations sound the same to me)
- 52. 52 Improving Cochlear Implants 1) Cochlear Implant + Hearing Aid in same ear Targets patients with reasonable low frequency hearing (usually with hearing aid) add a short CI electrode for high frequency stimulation Hearing aid CI Hearing CI Both Aid Only Only
- 53. 53 2) Bilateral cochlear implants are 2 implants better than one? 50% correct Bilateral With one CI there is no directionality NH 10 Bilateral CI 160 (Helms & Muller) Localization
- 54. 54 Bilateral cochlear implants Benefit #2 Better speech recognition in noise. Noisy environments are common. Typical noisy environment For patients who do poorly with 1 CI a 2nd CI can lead to dramatic improvement Hearing subjects score 100% in all three tests 100%
- 55. 55 The future of cochlear implants * Cochlear implant + hearing aid * Bilateral Cochlear implants to provide directionality, and, especially, improved speech recognition in noisy environments. * Increasing the number of channels/greater cochlea coverage to provide fine spectral information improved speech performance & improved music appreciation * Reducing power fully implantable device * CI performance limited by number of surviving auditory nerve neurons: regeneration of neurons
- 56. 56 Implants are a probe of speech recognition Exploiting tonotopic organization is the key •number of channels •frequency assignments to electrodes the CI learning curve demonstrates adult brain is plastic Implants enable the postlingually deaf to hear & in have provided sufficient information to support language development in children Summary: Implants, Neuroscience & Bio-engineering Implants, as the first prosthesis to successfully restore neural function, are a benchmark for biomedical engineering. Music/speech quality (recognition of male/female & accents) Requires fine spectral information which the present generation of CIs does not provide
- 57. 57 A Cochlear Implant is a wonderful example of the power of interdisciplinary science and technology: electrical engineering, computer science, mechanical engineering, physics, chemistry, and biology all working together in a tiny package inside a human being to improve the Human condition Final Thoughts There are about 150,000 implantees worldwide. With the latest devices ¾ of post lingually deaf adults can use a telephone, and small children can hear their parents voices and learn to understand them At a personal level 6 years ago I had my hearing restored. It has enabled me to more easily conduct research & teach, and hear my wife’s voice for the first time in 12 years and my daughter’s voice for the first time.
- 58. 58 This talk could not have been put together without the essential help of the following: At Purdue: Kirk Arndt & Steve Lichti (Physics) Donna Fekete (Biology) Beth Strickland (Audiology) Tom Talavage (ECE) At MedEl: Peter Knopp (Vienna) Jason Edwards (US), Amy Barco (US) Elsewhere: David Ashmore (London), Bill Brownell (Baylor), Phil Louzoi (UT Dallas), Richard Miyamoto (Indiana), Brandon Pletsch (IowaMed), Bob Shannon (House Ear Institute), Mario Svirsky (NYU), Fan-Gang Zeng (UC Irvine) Acknowledgements
- 60. 60 Brain I Cochlea Auditory Nerve Normal CI Cochlea Brain Auditory Nerve “c a t” Physical stimulus Neural coding Perception Compare a normal hearing person to a CI user to study the role of the cochlea in auditory processing Cochlear Implants are also research tools:
- 61. 61 Pitch estimate by place 0 10 20 30 40 50 60 70 80 90 100 2 4 6 8 10 12 14 16 18 20 22 Subject 1 Subject 2r Electrode Position (base to apex of cochlea) High pitch Low Pitch As CI user does not have a fine tuned cochlea (because the hair cells are non-functional) place pitch resolution is very poor (& there is a great deal of variability between subjects)
- 62. 62 1 10 100 apical electrode basal electrode Ineraid implant: DC 10 100 1000 5000300 Pitch estimate by rate High pitch Low Pitch Temporal coding for pitch upto 300 Hz But no matter how finely the pulse rate is varied, the implantee experiences pitch steps of 20 Hz (normal hearing (NH) discriminates in steps of 1-2Hz at 100 Hz NH uses tonotopic code to obtain frequency resolution at low frequencies Pulse rate (Hz)
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- 64. 64 22 20 18 16 14 12 10 9 8 7 6 5 4 3 2 1 0 5 10 15 20 25 30 35 mm Apex Base 184 513 1168 2476 5085 10290 20677 Hz Partial insertion Typical insertion 20 Sound Image Compression Cochlea is ~35 mm in length Electrode ~ 15-25 mm Only part of the auditory nerve is stimulated : typically 500- 5000 Hz. But most speech is 250- 6800 Hz. If we relay all frequencies of speech to the auditory nerve: frequency compression of the sound image. Visual examples
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- 69. 69 ca. 550 B.C. Pythagoras reasons that sound is a vibration of air. Sound
- 70. 70 Physical and perceptual characteristics of sound • Amplitude • Frequency • Complexity , and phase relationship of constituent frequencies • Loudness • Pitch • Timbre Physical Perceptual
- 71. 71 Acoustic Pressure is measured in decibels (dB) • 1 atm = 100,000 pascals • Threshold: the softest sound detectable is 20 micropascals (at 1000 Hz). 2 parts in 10 billion of an atmosphere • We hear sounds 1-10 million times more intense than threshold • dB are logarithmic units with 0 dB at threshold • adding 20 dB = factor of 10 increase in pressure
- 72. 72 Hearing threshold of a profoundly deaf person (ex: the speaker)Hearing threshold of a severely deaf person soft loud
- 73. 73 The Ear Has Three Distinct Regions ca. 550 B.C. Pythagoras & successors ca. 175 A.D. Galen Nerve transmits sound to the brain It has taken until the present to unravel the rest
- 74. 74 Why is our “sound sensor” not on the outside of our head? Impedance mismatch overcome by ratio of areas and lever action Hermann Ludwig von Helmholtz first to understand the role of the ossicles
- 75. 75 Action of ototoxic antibiotics on hair cells Loud noise also destroys hair cells
- 76. 76 Many of the differences in perception between natural hearing and hearing in people with cochlear hearing loss can be accounted for in terms of a loss or reduction in basilar compression. * Loss of gain (can’t hear softer sounds) * Reduced dynamic range * Loss of frequency sensitivity * Preferential loss of high frequency sensitivity. (Since hair cells at the base of the cochlea are more prone to damage.) Normal Hearing Don’t lose your hair…. cells
- 77. 77 Vowel perception by normal hearing listeners. Speech pattern recognition problem F1 and F2 values of English vowels (Peterson and Barney, 1952) Vowels are quite distinct •What features of the pattern of neural output from the cochlea •are most critical? Amplitude? Temporal? Place (frequency)? FormantFundamental
- 78. 78 Power function exponent (P) 0.05 0.2 0.50.1 PercentCorr 0 10 20 30 40 50 VOWELS CONSONANTS 0.3 0.5 0.8 2 31 CI electrodes span 20 dB normal hearing: 120 dB (but speech ~50 dB range) 50 dB input gives best result Input Dynamic Range Input Amplitude (Unit) 0 200 400 600 800 1000 OutputAmplitude(DynamicRange%) 0 20 40 60 80 100 p=0.30 p=3.0p=2.0p=1.5p=1.0 p=0.8 p=0.5 p=0.20 p=0.10 LOG Amin Amax Input Compression •Speech recognition is only mildly affected by large distortions in amplitude P P % Amplitude Study Output = (Input)p Pain (20dB) Just audible Implants Normal Hearing Output
- 79. 79 DAIP Consonants (20) Quiet n=7 Stimulation Rate (ppse) 11 µS/phase 1000 10000 InformationTransferred 0 20 40 60 80 100 16 Electrode CIS 12 Electrode CIS 8 Electrode CIS 4 Electrode CIS 16 Electrode QPS 12 Electrode QPS 8 Electrode QPS 4 Electrode QPS +10 dB SNR 1000 10000 •High stimulation pulse rates should better represent temporal features in speech. •No improved use of temporal cues in speech at higher rates observed % Correct 500/s 1000 /s 10000 /s Temporal Study Types of implant with variable numbers of channels & speech coding strategies stimulation pulse rate
- 80. 80 Hydrodynanic Model of the Basilar Membrane 2 2 2 0 0(1/ ) ( / )Z A M K Dω ω = − + 0 =frequency of stimulusf 0 mass =frequency of stimulus = damping stiffness A = area M D K ω = = 0 2= k / low Z resonancemω
Editor's Notes
- #11: .