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 B
rain
Sound and FrequencyP
ress
ure
TimeHigh Frequency
Low Frequency
Tones and the Cochlea
High frequency
Low frequency
Frequency Spectrum of Tones
Pow
er/M
agni
tude
Frequency
Power SpectrumGives an indication of what frequencies are present in complex signals
Time Domain
Frequency Domain
Summed signal
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-2
-1
0
1
2
+
Complex Sound SpectrumComplex sounds can be decomposed into individual frequency components…
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-2
-1
0
1
2
0 500 1000 1500 2000 2500 3000 3500 40000
100
200
300
400
500
Signal vs. Time
Frequency Spectrum
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
200Hz
400Hz
800Hz
1600Hz
3200Hz
200Hz400Hz800Hz1600Hz 3200Hz
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01-1
-0.5
0
0.5
1
Speech- Frequency Spectrum of Vowels
a e i
o u
6 kHz0 kHzFrequency
Pow
er
Spectrograms“Discover your true north”
Power spectrum plotted vs. time
1.5 2.0 2.5
Time (seconds)
10k
1k
100Fre
quen
cy (
Hz)0 0.5 1 1.5 2 2.5 3 3.5
x 104
-0.2
-0.1
0
0.1
0.2
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
LowFreq
HiFreq
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 HairCells
Electric Activation with Cochlear Implant
Hair Cells
Auditory Nerves
(The University of Melbourne)
Cochlear Implant FactsCochlear Implant FactsQuick 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: NucleusTM
Advanced Bionics: ClarionTM
Med-EL: Combi-40+TM
AllHear: AllHearTM single channelAntwerp Bionic Systems: LauraTM
(now owned by Cochlear)MXM Laboratories: DigisonicTM
* FDA survey of venders 11/2001 http://www.nidcd.nih.gov/health/pubs_hb/coch.htm#c
Cochlear Corporation: NucleusTM
FDAapproved
Cochlear Electrode Array
CochlearElectrode
Cochlea
AuditoryNerve
Cochlear Corporation’s Nucleus Electrode
What Do Cochlear Implants Sound Like?
1 Channel
4 Channel
8 Channel
2 Channel
base ap
ex
Auditory neuron cell bodies
Electrode 1 Electrode 2
Activated CellsActivated Cells
Independent Activation!
Electrode 1 Electrode 2
Channel interaction
Incr
ease
d D
ista
nce
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
electrodeCell 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
0
10
20
30
40
50
60
70
80
90
100
Med El CIS-Link Nucleus 22 Clarion v1.2
Scores on NU6/CNC words
Nucleus 24 ClarionHi-Focus
C II Hi Res.
Per
cen
t C
orr
ect
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)
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