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Cochlear Implants

Cochlear Implants



Introduction to cochlear implants given to freshmen engineering students at Ohio Northern University

Introduction to cochlear implants given to freshmen engineering students at Ohio Northern University



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Cochlear Implants Cochlear Implants Presentation Transcript

  • Re-Engineering Hearing: Introduction to Cochlear Implant Design Dr. Ryan Clement 04/30/08 GE 106: Freshman Engineering 3
  • Class Overview
    • Introduction to Cochlear Implants
      • Anatomy and Physiology of Hearing
      • Speech and Sound (Frequency Spectrum)
      • Cochlear Implant Design Principles
    • Brainstorming design session
      • New design concept for a cochlear electrode array
    • Ethics discussion exercise
      • The unexpected response from the deaf community
  • Key Concepts
    • Sound waves to neural impulses
    • Sounds and speech basics
      • Frequency Spectrum
      • Spectrograms
    • Electrical Stimulation of Cochlea
  • Normal Hearing- Anatomy External ear Middle ear Inner ear (cochlea)
  • How Do We Normally Hear? Sound enters ear… Ear drum the eardrum and middle ear bones vibrate… which creates a fluid wave in the cochlea… Transduced to neural impulses for brain to interpret
  • The Cochlea: Sound to Neural Impulses http://www.iurc.montp.inserm.fr/cric/audition/ Cross-section of Cochlea http://www.bcm.edu/oto/research/cochlea/Hearing/
  • Transverse Sound Wave Hair Cells Auditory Nerves To Brain
  • Sound and Frequency Pressure Time High Frequency Low Frequency
  • Tones and the Cochlea High frequency Low frequency
  • Frequency Spectrum of Tones Power/Magnitude Frequency Power Spectrum Gives an indication of what frequencies are present in complex signals Time Domain Frequency Domain Summed signal +
  • Complex Sound Spectrum Complex sounds can be decomposed into individual frequency components… Signal vs. Time Frequency Spectrum 200Hz 400Hz 800Hz 1600Hz 3200Hz 200Hz 400Hz 800Hz 1600Hz 3200Hz
  • Speech- Frequency Spectrum of Vowels a e i o u 6 kHz 0 kHz Frequency Power
  • Spectrograms “ Discover your true north” Power spectrum plotted vs. time 1.5 2.0 2.5 Time (seconds) 10k 1k 100 Frequency (Hz) Speech signal vs. time Di- -s- -c o v- er y- our t- r- ue N- o r th
  • The Cochlea is a Frequency Analyzer! Un-coiled Cochlea Low Freq Hi Freq
  • Sensorineural Hearing Loss
    • The loss of inner hair cells = deafness
    • Causes
      • Heredity
      • Genetic
      • Aging process
      • Ototoxic drugs
      • Excessive exposure to loud sounds
    Microscopic view of hair cells on basilar membrane. Outer Hair Cells Inner Hair Cells
  • Electric Activation with Cochlear Implant Hair Cells Auditory Nerves
  • (The University of Melbourne) Cochlear Implant Facts
    • Quick Facts:
      • candidacy : severe-to-profound sensorineural deafness
      • mechanism : electrical stimulation bypasses impaired cochlea
      • ~100,000 recipients worldwide (~21,000 in the U.S.) *
      • 50% children (12 mo-17 years); 50% adults *
      • Manufacturers:
        • Cochlear Corporation : Nucleus TM
        • Advanced Bionics : Clarion TM
        • Med-EL : Combi-40+ TM
        • AllHear : AllHear TM single channel
        • Antwerp Bionic Systems : Laura TM (now owned by Cochlear)
        • MXM Laboratories : Digisonic TM
    * FDA survey of venders 11/2001 http://www.nidcd.nih.gov/health/pubs_hb/coch.htm#c Cochlear Corporation : Nucleus TM FDA approved
  • Cochlear Electrode Array Cochlear Electrode Cochlea Auditory Nerve Cochlear Corporation’s Nucleus Electrode
  • What Do Cochlear Implants Sound Like? 1 Channel 4 Channel 8 Channel 2 Channel base apex
  • Auditory neuron cell bodies Electrode 1 Electrode 2 Activated Cells Activated Cells Independent Activation!
  • Electrode 1 Electrode 2 Channel interaction Increased Distance
  • Design Problem
  • 10 Minute Design Session!
    • New Electrode Concept
    • Break into groups of 4-5
    • Create a new electrode design that places the electrodes closer to the neuron cell bodies
    • Try to think of 2 strategies
    • Sketch the basic ideas
    • Discuss the pros/cons of each
    electrode Cell body
  • Actual Solutions- Advanced Bionics Electrode Positioner* *been attributed to 9 menengitis-related deaths and is no longer used
  • Actual Solutions- Cochlear Corporation The Nucleus Contour features a self-curling electrode array A stylet keeps the array straight during insertion, and then is removed by the surgeon The array then hugs the center of the cochlea (where the auditory neurons are)
    • Deaf Community
    • Two communities of the deaf:
    • - signers (Gallaudet, American Sign Language)
    • - vocalists (Central Inst for the Deaf, Alex. G. Bell)
    • History of device controversy
    • if children are taught “signing” from early on, they develop “easy, facile” communication with other signers
    • vocalists are taught to use whatever residual communication they have, augmented by hearing aids – large, bulky oral speech never “perfect”, communication-limited
    • Cochlear Implant (Prosthesis)
    • Pre- and Post-lingual deafness
    • adults who have developed language skills prior to CI use learn to use the prosthesis more easily
    • some infants, even with extensive training never learn to use the implant to communicate
    • adult-onset deafness, difficult to learn sign-language, not controversial to employ CI
    • Anti-cochlear implant arguments – for children
    • dangerous surgery, possible infections, weakens skull
    • just another hearing aid providing limited communication
    • vocalist children “mainstreamed” often frustrated & angry
    • superior social development of “signers” w/ signing family
  • Ethical Dilemmas- Cochlear Implants Imagine that you and your spouse are deaf. Your child is born without hearing. Would you go forward with the implant? What are all the issues you would consider? Would your reasoning change if you both could hear?
  • Speech Processing
  • Performance Results
  • Dorman 2002
  • Factors Effecting Cochlear Implant Performance
    • Duration of deafness
    • Age of onset of deafness
    • Age at implantation
    • Duration of cochlear implant use
    • Emersion in hearing world
    • Other:
      • Number of remaining auditory nerve fibers
      • Electrode placement and insertion depth
      • Dynamic range
    • Commitment!! (family and individual)