Cochlear Implants

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)

COCHLEAR IMPLANT ETHICS

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)

Cochlear Implants

by RyanClement

Accessibility

Categories

Upload Details

Usage Rights

Statistics