PROGRAMMING

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PROGRAMMING
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MAPPING

• Individual patients have different perceptions
  resulting from electrical stimulation to the
  cochlea
• ie the strength of the stimulation required to
  elicit auditory perceptions of the same loudness
  is different from patient to patient, and from
  channel to channel for the same patient
• Patients differ in their ability to perceive
  pitch changes resulting from stimulation of
  different channels

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MAPPING

• The CI can be programmed to fit the
  psychophysical requirements of individual implant
  recipients
• The combination of all these individualised
  parameters is called a MAP
• MAPping is a PROCESS by which the optimal
  programming parameters are determined for each
  individual patient

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Speech Processing Strategies
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SPEAK

• Continuously analyzes the energy in the incoming
  acoustic signal and determines the spectral
  maxima.
• Spectral maxima frequency regions in the
  waveform that contain the greatest amounts of
  energy.
• Selection of only the highest amplitude spectral
  maxima increases the probability that speech
  rather than noise (static) is presented.

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SPEAK
Analysis bandwidth 116 to 7787 Hz Select the
spectral maxima Sequentially stimulate the
channels representing those frequency bands
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SPEAK

• Amount of current applied to each channel is
  within the dynamic range (the difference between
  C-level and T-level).
• Acoustic input varies continuously over time, so
  the spectral maxima will change and the channels
  selected for stimulation will vary across the
  array.
• Average no. of maxima 6 8 (max 10)
• Actual no. depends on signal spectral
  composition, signal intensity and the MAP.

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SPEAK

• The channels selected for stimulation represent
  the largest spectral peaks.
• They are stimulated in tonotopic order from high
  to low frequency.
• Stimulation rate 250 pps (overall rate 2500
  pps)
• For broadband signals more maxima, slower
  stimulation rate
• For sounds with limited spectral content less
  maxima, higher stimulation rate

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SPEAK
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SPEAK

• SPEAK in SPrint
• Stimulation rate
• 250 Hz per channel (fixed)
• Not affected by high T/C levels
• Not affected by wide P.W. (lt 200 usec)
• SPEAK in ESPrit
• Selects 8 maxima (default)
• Max. PW 37 usec
• Requires at least 12 channels
• Alter apical gains if sound different to SPRint
  using the gain shaper

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CIS

• Continuous interleaved sampling
• Uses smaller no. of channels at a higher
  stimulation rate per channel to represent the
  temporal changes.
• Channel selection is fixed.
• You may choose to use 4, 6, 8 or 12 channels.
• Due to the power demands of this strategy, it was
  used only with the SPRint speech processor. It
  is currently available in ESPrit using lower
  stimulation rate.
• Monopolar modes only

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CIS

• You choose the no. of electrodes being used.
• A bandwidth is assigned automatically to each
  one, following the tonotopic order of the
  cochlea.
• During stimulation, the output amplitudes from
  each band are measured and represented as
  variations in the amount of current sent to the
  channels.
• The current delivered is directly proportional to
  the energy in the band and is within the dynamic
  range.
• Permissible stimulation rates per channel
• 900, 1200, 1800 and 2400 Hz
• (max overall rate lt 14400 Hz)

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CIS
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CIS
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CIS Secondary Parameters

• Jitter
• Recommended 10-20 jitter.
• May reduce pinging or bursty in onset at
  higher rates and reduce buzz percepts at lower
  rates.
• Psychophysics
• Must be re-measured for different stimulation
  rates.
• Increasing stimulation rate will reduce T-level,
  but C-levels less affected.
• Increasing number of channels may require a
  global reduction in C-levels.

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ACE

• Advanced Combination Encoder
• ACE SPEAK CIS
• Encodes important spectral and temporal speech
  cues
• Flexibility to meet individual needs
• No. of maxima up to 20
• Stimulation rate per channel 250, 500, 720,
  900, 1200, 1800 or 2400 (overall up to 14400 Hz)
• 6 maxima stimulation rate per channel 2.4 kHz
• 20 maxima stimulation rate per channel 720 Hz
• Monopolar modes only

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ACE
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COMPARISON OF STRATEGIES
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Stimulation Modes
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STIMULATION MODES
Electrical stimulation produces current flow
between an active and an indifferent
electrode Stimulation Mode describes the
location of the indifferent electrode relative to
the active electrode The physical separation of
the active and reference electrodes determines
the spread of electrical current, hence
controlling the area over which nerve endings are
stimulated.
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STIMULATION MODES
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Monopolar (MP) Stimulation

• Active electrode is intracochlear but the
  indifferent electrode(s) is extracochlear.
• MP1 current flows between designated active
  intracochlear electrode and the ball electrode
  (R1)
• MP2 current flows between the active
  intracochlear electrode and the plate electrode
  (R2)
• MP12 current flows between the active
  intracochlear electrode and both extracochlear
  electrodes (R1 and R2)

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Monopolar (MP) Stimulation

• Why MP modes?
• Wide spread current flow
• Much lower current levels for T and C-levels.
• Lower energy consumption to produce auditory
  sensations
• Longer battery life
• Auditory nerve can be stimulated at a higher
  rates (good for both CIS and ACE)

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Bipolar (BP) Stimulation

• Current flows between two intracochlear
  electrodes
• Active indifference pair
• Examples
• Active Indifferent Total
  no. of channels
• BP 13 14 21
• BP1 13 15 20
• BP2 13 16 19

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Bipolar (BP) Stimulation

• The physical separation of these electrodes
  determines the spread of current and the area
  over which the spiral ganglion cells are
  stimulated.
• If T and C-levels are too high, a wider bipolar
  mode should be selected.
• As the bipolar configuration becomes wider, the
  number of available pairs or channels for
  stimulation decreases.

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Common Ground (CG) Stimulation

• Current flows between the designated active
  electrode and all other electrodes on the array
  inside the cochlea.
• Allows all 22 electrodes to be used as active.
• T and C-levels are typically lower than in BP
  mode.
• It is used diagnostically to detect electrode
  anomalies.

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Setting Stimulation Mode

• Try MP12 mode first.
• It provides the greatest flexibility.
• BP modes can use only the SPEAK strategy.
• CG modes can use only the SPEAK strategy.
• CG should not be used in cases of partial
  insertions of electrode array because there may
  be a higher probability of non-auditory
  sensations.
• Whenever you choose a different mode, T and
  C-levels must be re-measured in the new mode
  because the amount of current necessary to reach
  T and C-levels will be different in each
  stimulation mode.

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Frequency-to-Channel Allocation
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Frequency-to-Channel Allocation

• Electrodes are numbered sequentially.
• Tonotopic organization of the cochlea
• Electrode 1 Basal Highest pitch percept
• Electrode 22 Apical Lowest pitch percept
• Frequency-to-channel allocation depends on
• Speech processing strategy
• No. of channels available for stimulation in the
  MAP

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SPEAK

• Maximum no. of channels 20
• 16 frequency-to-channel allocation tables
• Table 1-6 divide overall bandwidth into 20
  channels
• Table 7-14 divide overall bandwidth into fewer
  channels when less than 18 active channels
  are available
• Default Table 6 (widest frequency range)
• 116 Hz to 7871 Hz
• There is less frequency selectivity in MAPs with
  limited numbers of channels.

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CIS and ACE

• Fixed default frequency range 187 7937 Hz
• 27 frequency tables
• Automatically allocate a frequency table
  according to no. of channels (412) available.
• If necessary, the high frequency cut off point
  can be reduced by lowering the frequency table
  number.

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Electrical Stimulation Levels
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Electrical Stimulation

• Charge-balanced biphasic current pulses

Pulse Width
Stimulus Amplitude
0 mA
Increasing the amplitude of the pulse and/or
widening the pulse width results in more
electrical charge being delivered
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Current Level and Pulse Width

• Current Level is expressed in arbitrary units.
• Current Level 1 (10 mA) - 255 (1750 mA)
• Default pulse width (PW) 25 ms/phase
• Narrow pulses take less time to deliver
• Therefore, higher rates.
• Pulse width 25 400 ms/phase
• Maximum pulse width depends on the coding
  strategy, the stimulation mode, the stimulation
  rate and the number of maxima or channels
  selected.
• Dont widen the pulse width unless the user does
  not receive sufficient loudness when using a
  narrow pulse at maximum current amplitude.

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Stimulus Amplitude-to-Current Level MAPping
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Automatic Gain Control

• To control the gain so peaks in the acoustic
  signals are limited to values that translate into
  stimulation at C-level.
• It rapidly decreases the gain so that the peak
  value of the signal is set to a fixed value.
• AGC slowly increases the gain after the
  high-level peak has passed.

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Microphone Sensitivity Control

• It determines the minimum input signal level
  required for stimulation.
• Higher sensitivity settings lower SPL is
  required to cause stimulation.
• Lower sensitivity settings louder sound is
  required to cause stimulation.
• For normal listening situations,
• Sensitivity 8 on Sprint
• Sensitivity 3 on ESPrit

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Microphone Sensitivity Control

• If microphone sensitivity is always set above or
  below the optimal settings
• Overall C-levels in MAP are not set appropriately
• If sensitivity is set too low
• Gain applied to incoming signal is reduced
• Soft sounds will not be processed and cannot be
  heard.
• If sensitivity is set too high
• Gain applied to low-level inputs is increased
• Low level noise will be heard and signal-to-noise
  level will decrease.

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Base Level

• Default 4
• Range 4 15 in SPEAK
• 0 15 in ACE and CIS
• Increasing the Base Level
• Increases the level of sound required to initiate
  electrical stimulation, and then reduces the
  background noise.
• Reduces the dynamic range
• Dont raise the Base Level unless it is
  necessary because it reduces the operating range
  of the processor.

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Q-value

• Controls the steepness of the amplitude growth
• Determines the percentage of the electrical
  dynamic range that is allocated to the top 10 dB
  of the speech processors channel amplitude
  range.
• The lower the Q-value, the steeper the amplitude
  growth function at the lower end.
• Default 20
• 80 of electrical dynamic range is MAPped into
  the top 10 dB of the processors range.
• The lower 20 of the individuals dynamic range
  is MAPped into the lower 20 dB of the processors
  range.

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Q-value

• Lowering Q-value
• Making soft sounds, including background noise,
  seem louder.
• Raising Q-value
• Soft voices may not be heard. May reduce a
  persons overall speech understanding ability.
• 20 50 for SPEAK
• 10 50 for ACE and CIS

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Autosensitivity Control (ASC)

• Reduce background noise.
• Looks at the troughs (noise floor) in the
  spectral enveolope.
• Gain decreases slowly

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Channel Gains

• To alter the perceived sound quality of the MAP
• Default setting 0 dB across all channels
• Gain is applied to each channel output and
  affects the stimulation levels sent to the
  implant.

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How do we modify the loudness percept?
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How to modify the loudness percept?

• Use the T/C-level modifiers to increase/decrease
  C-levels for all channels by a fixed percentage
  of the dynamic range during live-voice testing of
  the MAP.
• Use the T/C-level modifiers to increase/decrease
  T-levels for all channels by a fixed percentage
  of the dynamic range, making the low-level
  signals louder or softer. (Note You lower
  T-levels only when you think T-levels has
  over-estimated.)
• Lowing Q-value results in a louder perception of
  low-level signals, including background noise.

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How to modify the loudness percept?

• Raising the Base Level increases the minimum
  acoustic signal that results in stimulation.
• Use the volume control on the speech processor.
• 0 9 on SPRint
• 0 5 on ESPrit
• The volume control can only reduce the C-levels
  (total reduction is 25)

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Magnet
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Magnet

• The magnet strength can be adjusted by turning
  the magnet insert in the external coil.
• Magnet strength should be assessed and if
  necessary adjusted at first fitting.
• This is critical especially for children
• Magnet inserts strength ½, 1, 2, 3, 4 are
  available
• Magnet strength required will depend on thickness
  of skin flap, hair, swelling, fatty tissue etc

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Magnet

• Magnetic pull of magnet in headset should be as
  loose as possible but still firm enough to stay
  in place with movement of the head ie not to fall
  off head

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Magnet

• Skin Flap Thickness
• Receiver-stimulator will operate for separation
  of receiving and transmitting coils up to 6 to
  9mm
• If flap is thicker than 9mm
• the strongest magnet may not be strong enough
• the internal and external coil coupling will not
  be as effective as it should be
• the signal can be degraded

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Telemetry
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Objective Measurements

• electrode impedance
• compliance voltage
• neural response telemetry (NRT)

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Telemetry - purpose/benefits

• Impedance Telemetry
• Compliance Telemetry
• NRT Telemetry

• Measurement of electrode impedance and for
  integrity testing (Implant Test)
• Detection of out-of-compliance conditions which
  result in abnormal loudness growth
• Measurement of evoked auditory (neural) response

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Electrode Impedance

• electrode impedance is a measure of the
  opposition to electrical current flow through the
  lead wires, electrodes and tissue
• electrode impedance calculated by dividing the
  voltage at the electrode by the current flow
  through the electrode.
• impedance voltage/current

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Electrical Impedance

• can be used to detect conditions under which an
  electrode should not be used
• HIGH IMPEDANCE either the electrode lead wire
  is broken and open circuited, or the electrode is
  not in contact with body fluids
• SHORT CIRCUIT low impedance (in common ground
  mode) indicates that the electrode, or its lead
  wire, is in contact with another electrode or
  lead wire

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Compliance Telemetry

• compliance is the ability of the implant to
  deliver sufficient voltage to generate the
  desired current level
• out-of-compliance refers to the condition where
  the maximum voltage available from the implant is
  not sufficient to generate the desired current
  level

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Compliance Telemetry

• if implant is out-of-compliance
• the actual current delivered is less than the
  current level requested
• the patient does not perceive loudness growth
  when current level is increased
• the MAP will not provide appropriate loudness
  information

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Compliance Telemetry

• causes of out-of-compliance
• high electrode impedance
• high current level
• WinDPS will provide warning message if implant is
  out-of-compliance during T/C-level measurements
• resolving out-of-compliance problems
• goal is to reduce T/C levels
• use wide stimulation mode eg monopolar
• increase pulse width

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Neural Reverse Telemetry NRT

• The stimulation of the implant causes nerve
  fibers in the spiral ganglion to fire, which
  generates an action potential.This is the NEURAL
  RESPONSE.
• The implant records the action potential by
  amplifying signals from intracochlear electrodes.
  The action potential is encoded and transmitted
  back to the speech processor by radio frequency.
  This is the TELEMETRY.