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COCHLEAR IMPLANT
PRESENTED BY
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What is a Cochlear Implant?
The cochlear implant (CI) is aprosthetic replacement for theinner ear (cochlea) and is onlyappropriate for people whoreceive minimal or no benefitfrom a conventional hearingaid.
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continued
The cochlear implant bypassesdam aged par ts of the inner ear and
electronicallystimulates the nerveof hearing. Part of the device issurgically implanted
in the skull behindthe ear and tinywires are insertedinto the cochlea.
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The Fundamental Concept of
Cochlear Implant
To bypass the damaged hair cells.
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Hearing Aid Cochlear implant
Concept : Amplify sounds reaching the ear Direct stimulation of auditory nerve
Indications :SNHLDeaf ChildCHL, when surgery is not feasible due to various
reasons
(a) External partMicrophoneSpeech processorTransmitter coil
(a) Internal partReceiver stimulator
Electrode array
Types :(a) Non electrical Electrical(b) Air conduction type (MC) Bone conduction
type
(c) Implantable hearing aids
Depending on number of electrodes and channelsNucleus 24 contourClarion C 11MED-EL combi 40+
Advantages :i. Cost effective as compared to cochlear implantii. Good patient complianceiii. Used in patients where surgery is not feasibleiv. Done on OPD basis
i. Better efficacy in postlingual deaf casesii. Better results in children in prelingual deafnessObserved in terms of
Speech intelligibility scoresLanguage development rate expressive skills
i. More useful for patients having profound SNHL
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Disadvantages
i. May cause intolerable distortion of sound inpatients with SNHL
ii. Difficult to use in patients with discharging earor otitis external (Bone conduction type can beused in these cases)
i. Cost factorii. Can not be used in psychologically imbalanced
individualsiii. Involves surgical procedure (technically difficult)iv. Long postoperative rehabilitation programmesv. Longer programmes hospital stay
Complications :
1. Recurrent infections of external auditory canaland middle ear
1. Facial nerve palsy2. Wound infection/dehiscence3. Device failure (early/late)4. CSF leak (rare)5. Post op vertigo6. Post op meningitis (rare)7. Extrusion/exposure of device (rare)
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Auditory Nerve Potentials
The work of Wever and Bray(1930) demonstrated that theelectrical response recorded
from the vicinity of theauditory nerve of a cat wassimilar in frequency andamplitude to the sounds to
which the ear had beenexposed.
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The Importance of the Cochlea
Meanwhile, the Russianinvestigators Gersuni and Volokhovin 1936 examined the effects of an
alternating electrical stimulus onhearing. They also found that hearing could
persist following the surgicalremoval of the tympanicmembrane and ossicles, and thushypothesized that the cochlea wasthe site of stimulation.
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Stimulating the Auditory Nerve
In 1950, Lundbergperformed one of thefirst recorded attemptsto stimulate the auditorynerve with a sinusoidalcurrent during a
neurosurgical operation.His patient could onlyhear noise.
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Tonotopic Stimulation Simmons, in 1966, provided a
more extensive study in whichelectrodes were placed throughthe promontory and vestibuledirectly into the modiolarsegment of the auditory nerves
The nerve fibers representingdifferent frequencies could bestimulated
The subject demonstrated that inaddition to being able to discernthe length of signal duration,some degree of tonality could beachieved
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The House 3M Single-Electrode Implant
In 1972, a speech processor was developed tointerface with the single-electrode implant and it wasthe first to be commercially marketed as the House/3M cochlear implant
More than 1,000 of these devices were implantedbetween 1972 to the mid 1980s
In 1980, the age criteria for use of this device waslowered from 18 to 2 years and several hundredchildren were subsequently implanted
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Multi-Channel Implants
During the late 70s, work was also being donein Australia, where Clark and colleagues weredeveloping a multi-channel cochlear implantlater to be known as the Cochlear NucleusFreedom
Multiple channel devices were introduced in
1984, and enhanced the spectral perceptionand speech recognition capabilities comparedto Houses single -channel device
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Anatomy
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AnatomyScala tympani
Scala vestibuli
Cochlear duct
Basilar membrane
Vestibular membrane
Tectoral membrane
Hair cells (outer/inner)
Cochlear nerve fibers
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Physiology of Hearing
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Anatomy
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Anatomy of Sound
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Th t f d i h d b th t l d th d i h d b th iddl
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The spectrum of sound is shaped by the external ear, and the sound pressure is enhanced by the middleear. Changes in pressure move the basilar membrane, which moves the tectorial membrane, which
moves the stereocilia of the hair cells. Ions flow into the hair cells. Outer hair cells vibrate and boostthe basilar membrane motion. Inner hair cells release neurotransmitter that leads to action potentials
in the auditory nerve fibers that contact the inner hair cells, which are transmitted to the brain
Action potentials
If l f d th k f th th b il b ti i
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If a low-frequency sound occurs, the peak of the the basilar membrane motion istoward the apex of the cochlea, and the action potentials are phase locked to the low
frequency. If a high-frequency sound occurs, the peak of the basilar membranemotion is toward the base of the cochlea, and if the frequency is high enough, the
action potentials will not be phase locked to the sound
Low frequency
High frequency
Action potentials
The computer contains a bank of band pass filters that splits the incoming
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The computer contains a bank of band-pass filters, that splits the incomingsound into a series of frequency bands. The intensity of the sound in each
frequency band is scaled by the amplitude compressors-- so that it fits withinthe dynamic range of the auditory nerve fibers (a point to which we shall
return). Then the output of each bandpass filter is delivered to one electrode.
Low frequency sounds stimulate apical electrodes, and therefore more apicalneurons, High frequency sounds will stimulate basal electrodes and thereforemore basal neurons
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The purpose of the bank of bandpassfilters, connected to electrodes in
different positions in the cochlea is torepresent the
waveform of sound amplitude spectrum of sound
phase spectrum of sound
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ELECTRODE POSITIONING
There are several ways in which the rate-place code in an implant differs fromthat in a normal ear.
In a normal cochlea you have about 3000 inner hair cells arrayed along thebasilar membrane, each of which reports on incoming sound in terms of its
position along the array, the timing of its firing pattern and the rate at which itfires. This message is transmitted to the brain by lots of nerve fibers attached
to each hair cell.In the implanted ear, the 12-22 electrodes only cover the first turn of the
cochlea. The full range of audible frequencies therefore stimulate nerve fibersthat respond to middle- to high frequencies in the normal ear. The most apicalnerve fibers are not stimulated. Whether this would be a problem was hard topredict. It may be that the brain expects to receive information about certainfrequencies from certain places in the cochlea. Or it may be that the we can
learn to use the neurons that are stimulated to get information about whatever
frequencies stimulate them.
I l hl th t d t h f th 3000 i h i ll
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In a normal cochlea the neurons connected to each of those 3000 inner hair cellsarrayed along the basilar membrane responds to a band of frequencies that is
about 1/3 octave wide.In the implanted ear, there are at most 22 electrodes, so entire audible frequencyrange has to be divided into 22 bands, each will be fairly wide, compared to the
bandwidth of the inner hair cells in normal ear. NO OF ELECTRODE DETERMINE THE BANDWIDTH EACH CARRIES
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Current from a single electrode spreads along cochlea and excites manyauditory nerve fibers
Electrical current spread also increasesthe bandwidth to which each nerve
fiber responds
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The combined effect of the reduced number of frequency bands and current spread could be tomake frequency selectivity at the level of the auditory nerve poor.
FREQUECY SELECTIVITY MAY BE POORER OF NEURON STIMULATED BY CI DUE:(1)The neurons are damaged.
(2)The outer hair cells are malfunctioning.
(3)The implant has a rather small number of electrodes and they may not act independently
Auditory nerve fiber stimulated by a cochlear implant
Frequency (kHz)
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Each filter + other devices + electrode = one channelWe would say that cochlear implant has fewer frequency channels than a normalear, and that each carries information about a broader range of frequencies in the
implant.
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Simulations with normal hearinglisteners
It is possible to manipulate sounds so that the number of frequency channels available to a normal hearing listener isreduced.
You cant just filter the sound the normal ear can just filter
the filtered sound so that its back to normal. Speech is filtered into 1 to 4 frequency bands in this figure.
Then the overall amplitude envelope in each band ismultiplied by a band of noise. So what the listener knows isthat in this broad frequency band, the sound is going up anddown in amplitude in a certain way-- they lose all the otherfrequency information-- just like a cochlear implant listenerwould. The demo plays the same sentence
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Cochlear-implant simulation
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-6
-4
-2
0
2
4
6
8Wavefo rm of Original Sound
Time (sec )
A m
p l i t u d e
TextEnd
Time
F r e q u e n c y
TextEnd
Spectrogram of Original Sound
0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
2000
4000
6000
8000
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-1
-0.5
0
0.5
1
1.5
2x 10 4 Simulated wavef orm
Time (sec )
A m
p l i t u d e
TextEnd
Time
F r e q u e n c y
TextEnd
Spectrogram of simulated wavefor m
0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
2000
4000
6000
8000
From herrick_uedamodel/script_demo1:best 6 of 16 channels, 250 Hz pulserate, 16 kHz sampling H/U filterbank
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ShannonImplantDemo
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Simultaneous sentences
same Fo difft Fo & VTdifft Fo
Shannon 4-channel implant simulation
summer ignore difft Fo difft Fo & VT
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Normal hearing listeners could get close to perfect performance onconsonant, vowel and even sentence identification with only 4 frequency
bands, or channelsSimulation results
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Later studies showed that normal hearing people needed more frequency bands tounderstand speech in noise. This figure shows the result of another study of normal)
increased as the number of bands increased up to about 16 bands. But when thematerials were presented in noise, the normal people hearing didnt do as well, and even
with 16 frequency bands, they did worse than in quiet.. It shows that in quiet the open symbols peoples speech recognition performance(with different materials than in the Shannon et al study So we need more frequency
bands in noise.. Implant listeners tested on the same speech materials in quiet, go about 10% correct equivalent to 9-10 bands in the normal hearing group it is as if the CI users have 9-10
channels available to them even though their implants provide them with 22 bands.Even more striking is that implant listeners only got 6-7% correct in noise it is as if
they only have 4 frequency channels to use.
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Engineering: attempts to improve frequencyselectivity
Pulsatile processing Electrode configuration monopolar, bipolar Current steering
theory is that current flow leads to channel
interactions we present different frequenciesthrough different electrodes, but the electrodes allstimulate the same neurons. CI manufacturers haveworked on ways to make the stimulation patterns
more frequency specific.
PULSATILE PROCESSING
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PULSATILE PROCESSING
Instead of simply delivering an analog current the waveform of the sound ineach frequency band to the nerve fibers, each electrode presents a series of
pulses. Hence pulsatile. But the pulses are not presented exactlysimultaneously they are delivered in sequence, but very rapidly. Because the
pulses are not on simultaneously they, cant add together (so -calledinteraction).
This is a more detailed account of pulsatile processing, with what is called continuous interleaved
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sampling (pulses are interleaved, not simultaneous). The top panel is the schematic of the device.The middle panel is the schematic of the parts of the processor a filter bank, just like before, and
then a device that takes off the envelope of the sound and throws away the fine structure. Thenthe envelope waveform in each channel gets multiplied by a series of pulses. When the waveform
is big, the pulse is big, when the waveform is small, the pulse is small.
The actual changes in the electrical signal waveform are shown in the bottom panel. The rightmost graphs show what is actually delivered to the nerve fibers in cochlea . Pulsatile Processing:
Continuous Interleaved Sampling (CIS)
El t d fi ti
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Electrode configuration One attempt to improve frequency selectivity is to change the way that the electric currents flow.In the monopolar configuration, the ground electrode is the most basal electrode, and that is theground for all of the other electrodes. That means that the pattern of current flow is pretty broad.In a bipolar configuration, each electrode is paired with its own ground electrode the one next
to it in the array. That makes a much narrower pattern of current flow. A narrower pattern of current flow will excite a more restricted set of neurons, and that is what we are after.
In fact, people have narrower tuning curves with bipolar than with monopolar configurations.
Monopolar
Bipolar
Ad d bi i ith thi id th t ld di id
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Advanced bionics came up with this idea that you could dividethe information between two electrodes to steer the current
toward different groups of neurons .
Idea: steer current
to places betweenelectrodes
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Electrode Configurations: Enhanced Bipolar Electrode (ENH) Diagonal electrode pairs provide a wider electrode
separation so that loudness growth can be achieved withbipolar stimulation.
ENH+Electrode Positioning System (ENH+EPS)
EPS pushes electrode array towards the modiolus, wherethe spiral ganglion cell bodies reside
High Focus Electrode+EPS (HF+EPS) Longitudinally-arranged plate electrodes orient the current
field toward spiral ganglion cell bodies "dielectricpartitions" designed to reduce current spread to adjacent
electrodes
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Processing strategies
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Perception of Speech
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Introduction toSpeech Processing
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The Speech Signal
Speech communication is the transfer of information via speech, either between persons orbetween humans and machines.
Language is one of the most important of humancapabilities. This makes it an ideal form of
communication between humans and machines.
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SPEECH ORGANS The Lungs and Thorax
Generate the airflow that passes through thelarynx and vocal tract.
Larynx and Vocal Folds/CordsObstruct airflow from the lungs to create turbulentnoise or pulses of air.
Vocal TractProduces the many sounds of speech by:Modifying the spectral distribution of energy andContributing to the generation of sound
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The Vocal Folds
Control the fundamental frequency (F0 ) of a speaker'svoice by controlling the rate of vocal fold vibration when airpasses between the folds.
Sound produced with vocal fold vibration are called voiced .
Sounds without vocal fold vibration are called unvoiced .
Turbulence may also be created using the vocal folds forthe production of sounds like /h/ and for whisperedsounds.
MANNER OF ARTICULATION
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MANNER OF ARTICULATION Manner of articulation describe the configuration in vocal tract
Different manner of articulation categories are
:CATEGORY DESCRRIPTION EXAMPLEVOWEL Little constriction of the vocal
tract BatDIPTHONONG Vowel with changing
configuration bay
GLIDE Transient sounds with fixedstarting points way'
Liquid Greater obstruction that vowels ray'NASAL All the air passes through the nose mayFRICATIVE Restricting airflow to create
turbulencesay
AFFRICATE Plosive followed by fricativesound jay
PLOSIVE Closure of air passage then release bay
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Indian Language properties Scripts used are phonetic in Nature
Better Articulatory discipline
Systematic manner of production
Five or Six distinct places of Articulation
Various types of Flaps/Taps or Trills
Fewer fricatives compared to English / European languages
Presence of retroflex consonants
A significant amount of vocabulary in Sanskrit with Dravidian orAustroasiatic origin gives indications of mutual borrowing and counterinfluences.
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Place of Articulation
Place of articulation describes the configuration of the vocal tract that distinguishes between the
phonemes within a manner of articulation group.
These are generally controlled by the position and
shape of the tongue, though for some sound teethand lips are important articulators
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Speech Sounds
Coarseclassification with phonemes .
A phone is theacoustic realizationof a phoneme.
Allophones arecontext dependentphonemes.
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Phoneme Hierarchy
Speech sounds
Vowels ConsonantsDiphtongs
PlosiveNasal Fricative
Retroflex
liquid
Lateralliquid
Glide
iy, ih, ae, aa,ah, ao,ax, eh,er, ow, uh, uw
ay, ey,oy, aw
w, y
p, b, t,d, k, g m, n, ng f, v, th, dh,
s, z, sh, zh, h
r
l
Language dependent.About 50 in English.
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Speech Waveform Characteristics
Loudness Voiced/Unvoiced.
Pitch. Fundamental frequency.
Spectral envelope.
Formants.
Speech Waveform
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Speech WaveformCharacteristics Cont.
Voiced Speech Unvoiced Speech
/ih/ /s/
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Short-Time Speech Analysis
Segments (or frames, or vectors) are typicallyof length 20 ms. Speech characteristics are constant.
Allows for relatively simple modeling. Often overlapping segments are extracted.
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Categorical Perception Experience of percept
invariances in sensoryphenomena that can be variedalong a continuum.
Can be inborn or can be induced
by learning. Related to how neural networks
in our brains detect the featuresthat allow us to sort the things inthe world into separatecategories
Area in the left prefrontal cortexhas been localized as the placein the brain responsible forphonetic categorical perception.
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Perception of Vowels
/a/ vowel has greatest intensitywith unvoiced / / as weakestconsonant
Front vowels perceived on basis of F1 frequency and average of F2and F3, whereas back vowels areperceived on the basis of theaverage of F1 and F2, as well as F3
So is it the absolute frequency
values of the formants? Or the ratio of F2 to F1? Perhaps it is the invariant cues
(frequency changes that occur withcoarticulation
F1
F2/F3
F1/F2
F3
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CI Speech Coding Strategies ACE: Unique to Cochlears Nucleus 24 CI system. ACE
optimizes detailed pitch and timing information of sound.
SPEAK: (spectral peak) Increases the richness of important pitch information by stimulating electrodesacross the entire electrode array.
MPEAK: multipeak
CIS: (Continuous-Interleaved Sampling) This high ratestrategy uses a fixed set of electrodes. Emphasizes thedetailed timing information of speech.
ACE (Advanced Combination Encoder)
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( )Strategy
Sound enters the speech processor through the microphone and
is divided into a maximum of 22 frequency bands. Up to 20 narrow-band filters divide sound into corresponding
frequency (pitch) ranges. Each frequency band stimulates a specific electrode along the
electrode array. The electrode stimulated depends on the pitch of the sound. Forexample, in the word "show," the high pitch sound (sh) causesstimulation of electrodes placed near the entrance cochlea,where hearing nerve fibers respond to high pitch sounds. The low
pitch sound (ow) stimulates electrodes further into the cochlea,where hearing nerve fibers respond to low pitch sounds.
ACE varies the rate of stimulation of the electrodes with a totalmaximum stimulation rate of 14,400 pulses per second.
SPEAK
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SPEAK Sound enters the speech processor through the microphone and is
divided into 20 frequency bands.
SPEAK selects the six to ten frequency bands containingmaximum speech information.
Each frequency band stimulates a specific electrode along theelectrode array.
The electrode stimulated depends on the pitch of the sound. Forexample, in the word "show" the high pitch sound (sh) causesstimulation of electrodes placed near the entrance of the cochlea,where the hearing nerve fibers respond to high pitch sounds. Thelow pitch sound (ow) stimulates electrodes further into thecochlea, where the hearing nerve fibers respond to low pitchsounds.
SPEAK's dynamic stimulation along 20 electrodes allows you toperceive the detailed pitch information of natural sound.
CIS
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CIS Sound enters the speech processor through the
microphone.
The sound is divided into 4, 6, 8 or 12 bands dependingupon the number of channels used.
Each band stimulates one specific electrode along theelectrode array, sequentially.
The same sites along the electrode are stimulated for everysound at a fast rate to deliver the rapid timing cues of
speech.
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SpeL stragedy
This is a new approach to sound processing for cochlearimplants, currently under investigation in Melbourne,Australia. This scheme aims to reduce the perceptual problemsrelated to mapping input dynamic range to the limitedelectrical dynamic range of hearing and to compensate forloudness summation effects. It derives its name from SpecificLoudness, which describes the way loudness is distributedacross frequencies or electrode positions. SpeL takes the novelapproach of computing models of normal auditory perceptionand perception with electric stimulation. These models are
computed in real time and sound processing platform is beingdeveloped. The results confirm that the use of the modelsrestores loudness perception close to normal over an inputdynamic range of at least 50 dB and improves therefore speechunderstanding
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Sensorineural Hearing Loss
Death of hair cells vs.ganglion cells
Otte, et al estimated we
need 10,000 ganglion cellswith 3,000 apically to havegood speech discrimination
Apical ganglion cells tend
to survive better (?acoustictrauma)
Central neural systemplasticity
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Anatomy of Speech
Mix of frequencies Speech recognition is top -down process Formant frequencies: frequency maximum based on
vocal tract F0 is fundamental frequency F1 & F2contribute to vowel identification F3l,r (lateral and retroflex glides) F4 & F5higher frequency speech sounds Some speech based on amplitude k, f, l, s
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Structure of Cochlear Implant
1. External components
2. Internal components
Components of Cochlear Implant
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Components of Cochlear Implant
Four Basic Parts of a
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Cochlear Implant
A microphone , which picks upsound from the environment;
A speech processor , which selectsand arranges sounds picked up by
the microphone;
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Continued
A transmitter and receiver/ stimulator , whichreceive signals from the speech processor andconvert them into electric impulses;
And electrodes , which collect the impulsesfrom the stimulator and send them to the
brain.
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Amplification
Occurs within the processor
Amplifiers used to increase the signal levels
Gain of amplifier determines the amount of increase
Gain = ratio of output signal level to input signal level
Can increase or decrease signal level
C i
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Compression
Impaired hearing has decreased acousticaldynamic range - 10 to 25dB.
Linear and non-linear compression. Gain of amplifier changed so output to input
ratio changes - automatic gain control. Automatic gain control - keep output voltage
in a certain range. Wide range of compressor types in use.
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Filtering
Filter on the basis of frequency - 100 to 4000Hz Three types: low pass, high pass, and band pass Two reasons for filtering:
1) remove unwanted information 2) separate bands for independent processing
Extract frequency dependent features Divide acoustic frequency spectrum into channels Feature extraction systems - filter F0, F1, and F2 Multichannel processing refers to multiple filtered bands
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Encoding
Encoded to transmit to the receiver
Preserves information and enables information to
get to the auditory nerve
Analog signal first enters the processor
One type - changes analog to radio-frequency
Another - converts from analog to digital
T f C hl I l
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Types of Cochlear Implants
Single vs. Multiple channels Audio example of how a cochlear implant sounds withvarying number of channels
Monopolar vs. Bipolar
Speech processing strategies Spectral peak (Nucleus) Continuous interleaved sampling (Med-El, Nucleus,
Clarion) Advanced combined encoder (Nucleus) Simultaneous analog strategy (Clarion)
N l F d B d W S d P
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Nucleus Freedom Body Worn Sound Processor Sound Processing Module
Microphone(s)
Transmitting Cable/Coil
Coil & Magnet
Controller
Controller Shoe & Cable
Batteries or RechargeableBattery Module
Nucleus Freedom Standard BTE Sound
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Processor Sound Processing Module
Microphone(s)
Transmitting Coil/CableCoil
Coil & Magnet
Controller
Batteries or RechargeableBattery Module
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Nucleus Esprit 3G Sound Processor
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Nucleus Esprit 3G Sound Processor
Sound Processor
Microphone(s)
Transmitting Cable/Coil(missing in slide)
Coil & Magnet (missing in slide)
Controls
Battery module
Nucleus Sprint Body Worn Sound
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ProcessorSound ProcessingModule & Controller
Microphone(s)
Short Transmitting Coil
Coil & Magnet
Long Transmitting Coil
Batteries orRechargeable BatteryModule
Advanced Bionics Harmony BTE Sound
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Advanced Bionics Harmony BTE SoundProcessor and Components
Sound Processing Module& Controller
Microphone & Ear Hook
Transmitting Cable/ Coil
Coil & Magnet
Rechargeable BatteryModule
Advanced Bionics Harmony BTE Sound
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There are two other models of BTE processors
Auria Platinum/CII BTE
Advanced Bionics Harmony BTE SoundProcessor and Components
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MED-EL Ear-level Speech Processors
Tempo+/OPUS 1 Program/volume
switches Sensitivity dial
OPUS 2 Switch free design FineTuner
MED EL Tempo+ BTE Sound Processor
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MED-EL Tempo+ BTE Sound Processor Sound Processing
Module & Controller
Microphone(s)
Transmitting Coil &Magnet
Transmitting Cable
Ear Hook
Battery Module
MED EL Opus BTE Sound Processor
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MED-EL Opus BTE Sound Processor
Sound Processing Module &Microphone(s)
Coil & Magnet
Transmitting Cable
Ear hook
Battery Module
Connecting piece
A f C hl I l
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Anatomy of a Cochlear Implant
H D CI W k?
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How Does a CI Work?
Sound is received by anmicrophone that rests over the earlike a behind-the-ear hearing aid.
Sound is sent from the microphone
to the signal processor by a thincable.
Signal processor translates thesound into electrical codes.
Codes are sent by a thin cable tothe transmitter held to the scalp byits attraction to a magnetimplanted beneath the skin.
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continued Transmitter sends codes across theskin to a receiver/stimulatorimplanted in the mastoid bone.
Receiver/stimulator converts thecodes to electrical signals.
Electrical signals are sent to thespecified electrodes in the arraywithin the cochlea to stimulateneurons.
Neurons send messages along theauditory nerve to the centralauditory system in the brain wherethey are interpreted as sound.
Neural Responses to Sound
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Neural Responses to Sound
1. Temporal coding: Provide information abouttiming cues (rhythm and intonation.
2. Place coding: Rely on the tonotopicorganization of a neural fibers.
3. Provide information about quality (timber of aspeech signal sharp to dull)
Sit f Sti l ti
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Site of Stimulation
1. Extracochlear
2. Intracochlear
3. Retrocochlear (lateral recess of thefourth ventricle over the cochlear
nuclei.
Sti l
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Stimulus
a. Stimulus type:
- Analog (continuous)
- Digital (pulsatile)
b. Stimulus configuration
1. Bipolar localized site of stimulation
2. Monopolar stimulates largepopulation of neurons
S h C di g
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Speech Coding
As speech is produced, the mouth, nose & pharynxmodify the frequency spectrum so that peaks andformants are produced at certain frequencies. Speechprocessing used 3 formants:
F0 = 100 to 200 HzF1 = 200 to 1200 Hz
F2 = 550 to 3500 Hz
N b f Ch l
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Number of Channels
1. Single channel no place coding
2. Multi channel
Sti l ti M d
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Stimulation Mode
1. Simultaneous : More than oneelectrode is activated at a givensuccession - CIS
2. Sequential : A continuous series of
electrode activates in succession -speak
Electrode Design
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Electrode Design
1. Single electrode
2. Multi electrode
Indication for Cochlear Implant
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Indication for Cochlear Implant
Adults 18 years old and older (no limitation by age)
Bilateral severe-to-profound sensorineural hearingloss (70 dB hearing loss or greater with little or nobenefit from hearing aids for 6 months)
Psychologically suitable No anatomic contraindications Medically not contraindicated
Indications for Cochlear Implantation
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-Children
12 months or older Bilateral severe-to-profound sensorineural hearing loss with
PTA of 90 dB or greater in better ear
No appreciable benefit with hearing aids (parent survey when5 yo)
Must be able to tolerate wearing hearing aids and show someaided ability
Enrolled in aural/oral education program No medical or anatomic contraindications Motivated parents
Factors Affecting Patient Selection
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Factors Affecting Patient Selection
a. Onset of deafness (congenital or adventitious)b. Year of deafnessc. Length of sensory deprivation (i.e. no hearing
aids)d. Socioeconomic factorse. Educational levelf. Individual ability to use minimal cuesg. General health
Factors Affecting Pt (cont )
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Factors Affecting Pt. (cont.)
h. Personality
i. Willingness to participate in rehabilitation program
j. Language skills
k. Appropriate expectations
l. Desire to communicate in a hearing society
m. Psychological stability
n. Cochlear patency
Audiologic Evaluation
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1. Pure tone audiometry under headphones
2. Warble tone audiometry with a hearing aid in amonitored free field
3. Immittance testing
4. Speech recognition testing
5 Speech awareness testing
Audiologic Evaluation (cont.)
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g ( )
6. Environmental sounds (closed and open set)
7. Speech reading (lip reading) ability
8. Electrical response audiometry
9. Auditory discrimination
10.Transtympanic electrical stimulation (promontory orround window test)
Medical Evaluation
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Medical Evaluation
1. Clinical history and initial interview2. Preliminary examination3. Complete medical and neurologic examination4. Cochlear imaging using computed tomography
(CT or magnetic resonance imaging (MRI)5. Vestibular examination
(electronystagmography)6. Pathology tests7. Psychologic or psychiatric assessment or both8. Vision testing9. Assessment for anesthetic procedures
CT Findings
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CT Findings
ABSENCE OF COCHLEAR NERVE
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ABSENCE OF COCHLEAR NERVE
Cochlear aplasia .
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Facial nerve dehiscence.
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Labyrinthine ossification in a patient with ahi t f i iti d i l h i
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history of meningitis and sensorineural hearingloss.
Labyrinthine ossification in a patient with a
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history of meningitis and sensorineural hearingloss.
Cochlear dysplasia.
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Contraindications
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Contraindications
Incomplete hearing loss Neurofibromatosis II, mental retardation, psychosis, organic
brain dysfunction, unrealistic expectations Active middle ear disease
CT findings of cochlear agenesis (Michel deformity) or smallIAC (CN8 atresia) Dysplasia not necessarily a contraindication, but informed
consent is a must H/O CWD mastoidectomy Labyrinthitis ossificans follow scans Advanced otosclerosis
Surgical Procedure
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Surgical Procedure
The future site of the implant receiver is marked withmethylene blue in a hypodermic needle
This site at least 4 cm posterosuperior to the EAC,
leaving room for a behind-the-ear controller
Next, a postauricular incision is made and carrieddown to the level of the temporalis fascia superiorlyand to the level of the mastoid periosteum inferiorly
Anterior and posterior supraperiosteal flaps are thendeveloped in this plane
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Procedure
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Procedure
Next, an anteriorly based periosteal flap,including temporalis fascia is raised, until thespine of Henle is identified.
Next, a superior subperiosteal pocket isundermined to accept the implant transducer
Using a mock-up of the transducer, the size of the subperiosteal superior pocket is checked
Procedure
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Procedure
Next, using a 6 mm cutting burr, a corticalmastoidectomy is drilled
It is not necessary to completely blueline thesinodural angle, and doing so may interferewith proper placement of the implant
transducer
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Procedure
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Procedure
Using a mock-up of the transducer for sizing, a well isdrilled into the outer cortex of the parietal bone toaccept the transducer magnet housing
Small holes are drilled at the periphery of the well toallow stay sutures to pass through. These suture willbe used to secure down the implant
Stay sutures are then passed through the holes
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Procedure
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Procedure
Using the incus as a depth level, the facialrecess is then drilled out
Through the facial recess, the round windowniche should be visualized
Using a 1 mm diamond burr, a cochleostomy ismade just anterior to the round window niche
Procedure
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ocedu e
The transducer is then laid into the well andsecured with the stay sutures
The electrode array is then inserted into thecochleostomy and the accompanyingguidewire is removed
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Procedure
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Small pieces of harvested periosteum arepacked in the cochleostomy sround theelectrode array, sealing the hole
Fibrin glue is then used to help secure theelectrode array in place
The wound is then closed in layered fashionand a standard mastoid dressing is applied
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PAEDIATRIC B/L COCHLEAR IMPLANTS
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The potential benefits of bilateral implants are
threefold
Firstly, it ensures that the ear with the bestpostoperative performance is implanted
Second, it may allow preservation of some of thebenefits of binaural hearing: head shadow effect,binaural summation and redundancy, binauralsquelch, and sound localization
Third, it may avoid the effects of auditory deprivation
on the unimplanted ear
Bimodal Listening
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g
Bimodal listeners use a cochlear implant on 1ear and a conventional hearing aid on the
opposite ear
Results of studies with bimodal devices paved
the way for bilateral cochlear implantation
Head Shadow Effect
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When speech and noise come from different
directions, there is always a more favorablesignal-to-noise ratio (SNR) at one ear
The head shadow effect is about 7dBdifference in the speech frequency range, butup to 20 dB at the highest frequencies
With binaural hearing, the ear with the mostfavorable SNR is always available
Binaural Summation and Redundancy
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y
Sounds that are presented to 2 earssimultaneously are perceived as louder due tosummation
Thresholds are known to improve by 3 dB withbinaural listening, resulting in doubling of perceptual loudness and improved sensitivityto fine differences in intensity
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Binaural Squelch
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The auditory nervous system is wired to help in noisysituations
Binaural squelch is the result of brainstem nucleiprocessing timing, amplitude, and spectraldifferences between the ears to provide a clearerseparation of speech and noise signals
The effect takes advantage of the spatial separationof the signal and noise source and the differences intiming and intensity that these create at each ear
Localization
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Interaural timing is important
for directionality of low-frequency hearing
For high frequency hearing,the head shadow effect ismore important
Head and pinna shadoweffects, pinna filtering effects,and torso absorptioncontribute to spectraldifferences that can helpdetermine elevation of a
sound source
Auditory Deprivation
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Work with conventional hearing aids hasdemonstrated that if only 1 ear is aided, whenthere is hearing loss in both ears, speech
recognition in the unaided ear deterioratesover time
This effect has been shown in children withmoderate and severe hearing impairments(Gelfand and Silman 1993)
Complications:
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A. Intraoperative
1. Intraoperative cannot be placedappropriately.2. Insertion trauma3. Gusher
Complications (cont.):
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B. Postoperative
1. Postauricular flap edema, necrosis or separation2. Facial paralysis
3. Transient vertigo is more likely to occur on atotally nonfunctioning vestibular system.4. Pain is usually associated with stimulation of
Jacobsons nerve, the tympanic branch of theglossopharyngeal nerve.
5. Facial nerve stimulation6. Meningitis7. Device extrusion
Rehabilitation
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Tuning or mapping of the external processor tomeet individual auditory requirements after 3 - 4weeks post op.
1. Multisensory approach2. Bimodal stimulation3. Suprasegmental discrimination training4. Segmental discrimination and recognition
training5. Speech tracking6. Counseling
Post-Surgery Audiology Appointments
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Initial Activation Mapping/ Programming session
1 week post-activation 1 month post-activation Every 3 months for the first year After the first year,
Every 6 months for children Annually for adults
Mapping/Programming Defined:
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Verb : the process of setting of the electricalstimulation levels appropriate for thepatient to hear soft and comfortably loud
sounds.
Noun : (map) the product of mapping or
programming, which determines how thecochlear implant will deliver stimulation
Mapping/Programming Session
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Bilateral simultaneous Evaluation and programming of each individual
speech processor and both speech processorstogether
Bilateral sequential Focus on new ear
Goals for CI Programming
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1. To provide audibility for the range of speechsounds
2. Comfort for all sounds (speech,
environmental, music, etc.)3. Ultimately to provide a means for
communication and spoken language
development4. Balance loudness between ears
Validation of Programming
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Functional gain testing in soundfield
Responses to NBN or warble tones from 250-
8000 Hz
Speech perception
All testing conducted with individual speechprocessors and binaurally
Validation of Programming
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Speech Perception Tests Ling thresholds ESP GASP
MLNT LNT PB-K WIPI HINT-C HINT AzBio
Sentence Stimuli
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Sentence material Always administer 2 lists Administered at 60 dB SPL
HINT Sentences: (A/The) boy fell from (a/the) window. 4 / 6 (A/The) wife helped her husband. 2 / 5 Big dogs can be dangerous. 3 / 5
AzBio Sentences: He got arsenic poisoning from eating canned fish. 5/8 Visual cues are quite powerful. 3/5
Reprogramming
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Check impedances at every visit Track changes or stability over time
Telemetry=relates to the ability of theelectrode to deliver current to the
surrounding tissue Detection of short and open circuits
Telemetry
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Results
Impedances within normal limits
Short circuit
Open circuit
Objective Measures
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Electrophysiologic (NRT/NRI/ART) Measurement of how the nerve responds to
stimulation Use cautiously to create MAP/s Can be used to help train a child for listening games
ESRT Measurement of middle ear reflex to loud sounds
Elicited electrically through the implant Requires a patient to be free of ear infections and to
remain fairly still
Ling Six (Seven) Sound Test
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ConsiderNO SOUND
as the
7th
Sound
ah (/a/)oo (/u/)ee (/i/)
shsm
(Ling & Ling, 1978)
(Rosemarie Drous,Formerly of the
Helen Beebe Speech & Hearing
Center)
Ling Six Sound Test
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Sound 1 3 6 9 12 /u/ oo BothCIs
L-ONLYR-
ONLY /a/ ah
/i/ ee
/ / sh /s/ ss
/m/ mm
Distance for Detection/Recognition/ID
Early Speech Perception
(ESP) (Moog & Geers, 1990)
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(Moog & Geers, 1990)
Auditory Assessment
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Meaningful Auditory Integration Scale(MAIS) Robbins, Renshaw, & Berry, 1991
Infant-Toddler Meaningful AuditoryIntegration Scale (IT-MAIS) Zimmerman-Phillips, Osberger & Robbins, 1997
Infant-Toddler Meaningful AuditoryIntegration Scale
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Available from Advanced Bionics
10 Questions0-4 Rating Scale
(0=Never; 1=Rarely; 2=Occasionally; 3= Frequently; 4=Always)
Meaningful Auditory Integration Scale
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( Available from Advanced Bionics Corporation
Parent Interview
10 Questions(1a younger than age 5 years/1b older than age 5 years)
0-4 Rating Scale
(0=Never; 1=Rarely; 2=Occasionally; 3=Frequently;4=Always)
PEACH
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Parents Evaluation of Aural/Oral Performance of Children
Ching & Hill, 2007
11 Peach Items (6 Quiet; 5 Noise)Frequency Ratings (n=5) of Reported Behavior
(Never/Seldom/Sometimes/Often/Always)(0%, 25%, 50%, 75%, >75%)
PEACH
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AbstractThe PEACH was developed to evaluate theeffectiveness of amplification for infants and
children with hearing impairment by a systematicuse of parents observations .
The internal consistency reliability was .88, and thetest-retest correlation was .93.
The PEACH can be used with infants as
young as one month old and with school-aged children who have hearing loss ranging from mild to profound degree.
Test of Auditory Comprehension
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Ages 4-17 years Normative data based on age
ranges and better ear PTA Stimuli on audiotape
Screening task to start Hierarchical
Ceiling: 2 consecutive subtestfailures
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Intervention
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Integration of Cochlear Implants &/or Hearing Aids
and
AuditoryIntervention
A Perfect Marriage
Levels of Auditory Hierarchy
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Auditory/Sequential Memory Auditory Closure
Auditory Analysis Auditory Blending
Auditory Figure Ground Auditory Tracking Auditory Processing Auditory Understanding/
Comprehension
(adapted from Caleffe-Schenck)
Auditory Hierarchy Detection to indicate the presence/ absence
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Detection to indicate the presence/ absence
of sound (Alarm Clock / Wake-Up /Marching Games)
Auditory Attention to pay attention toauditory signals, especially speech, for anextended time.
Identification to indicate an understandingof what has been labeled or named or to labelor name something. (L to L Sounds //Recognition / Identification)
Auditory Hierarchy
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Auditory Memory / Sequential Memory tostore and recall auditory stimuli or differentlength or number in exact order.
Distance Hearing to attend to sounds at adistance. (FM Issue)
Localization to localize the source of sound.(Bird Call Localization)
Auditory Hierarchy
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Auditory Figure Ground to identify a primaryspeaker from a background of noise.
Auditory Tracking to follow along in the text of abook as it is read aloud by someone else or inconversation. (see De Filippo &Scott, 1978)
Auditory Understanding / Auditory Comprehension to synthesize the global meaning of spoken languageand to relate it to known information.
Cochlear implants have not solved :
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Noise, distance and reverberation Speed, depth and complexity of language
Hardware problems A CIwill malfunction Deafness a child is deaf when the CI is off The diversity of our deaf population
Cued Speech
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Educators and parents must safeguardlanguage development of deaf children
Because deaf children are diverse andbecause cochlear implants dont conquer
every obstacle, a visual representation of spoken language is essential
Visual component in oral programs
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Even oral and A/V programs use vision to clarifywhat is heard
Auditory Verbal mentions auditory sandwich Auditory Oral programs use Mouth Time,
Visible Speech.. Gallaudets programs use Visual Phonics Some oral and auditory verbal programs use
Rhythmic Phonetics.
Rehabilitation
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Rehabilitation
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Conclusions Cochlear implants are designed to mimic the
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Cochlear implants are designed to mimic the
rate-place code in the acoustic ear. The frequency channels in the CI are fewer
and broader than those in the acoustic ear.
The number of frequency channels availableto the typical user is even smaller than thenumber in the implant.
Nonetheless, CI users understand speech fairlywell in quiet, but have much more trouble innoise.
FUTURE RESEARCH
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1. Continue investigating the strengths and limitations of presentsignal processing strategies including CIS-type and SPEAK-typestrategies. development of signal processing techniques capable of transmitting more information to the brain.
2. Develop noise reduction algorithms that will help implant patientsbetter communicate in noisy environments.
3. Identify factors that contribute to the variability in performanceamong patients Knowing these factors may help us develop signalprocessing techniques that are patient specific.
4. Develop pre-operative procedures that can predict how well apatient will perform with a cochlear implant.
5. Design electrode arrays capable of providing high degree of specificity. Such electrode arrays will provide channel selectivitywhich is now considered to be one of the limiting factors inperformance.
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