Comps: cochlear implants

What is the CI signal path?

• Acoustic signal captured by the microphone
• Converted to digital signal in the sound processor
• Transmitted via electromagnetic induction
• Converted to electrical pulses in implant
• Electrical stimulation of cochlear nerve fibers

what are conductors?

electrons move freely through the material

what is insulators?

electrons are tightly bound together

what is voltage?

differences in electrical charge between two points

what is current?

the flow of electrons

What are higher voltage mean?

greater potential to move electrons

open circuit=

no current flow

closed circuit =

continuous path allowing for current flow

broken electrode lead=

open circuit within the CI

resistance is opposition to

Direct current

impedance is opposition to

alternating current

what influences impedance CIs?

determined by the electrode integrity

influenced by cochlear fluids and tissue

What are clinical implications of impedance?

• high impedance reduces available current

• could cause compliance

• requires pulse width adjustment during cochlear implant mapping

what is circuit?

• a complete path for electrical current

• requires a power source, conductors, and a return path

• CI stimulation occurs within a closed circuit

what are circuit components?

• current generator

• electrode lead

• intracochlear electrode contact

• cochlear tissue and fluid

• return (ground) electrode

why do return electrodes matter?

• current must return to complete the circuit

• ground electrodes provide a SAFE return pathway

• this is essential for simulation and telemetry

what is direct current?

• flows in one direction

• provided by batteries of the unit

• dangerous if delivered continuously to the cochlea

what is alternating current?

• the direction of the current alternates back and forth

• in this process, the CI uses biphasic pulses

• This helps prevent buildup of harmful charges

Why are biphasic pulses used?

• biphasic pulses- defined

• prevents electrotoxicity

• balances charge deliveries

what does capacitors in CIs do?

• helps prevent residual DC from reaching the cochlea

• stores charge during brief signal gaps

• this is essential for safety and signal stability

Clinical Importance of Capacitors

• Prevent neural damage

• Ensure charge-balanced stimulation throughout the electrode
  array

• Allows for safe, long-term implant use

What is Electromagnetic Induction?

Electrical current generates magnetic fields
• Magnetic fields induce current in nearby conductors
• Enables wireless power and data transfer

Transmitting and Receiving Coils

External processor coil transmits the signal
• Internal implant coil receives the signal
• The skin does not block magnetic fields throughout the process

Near-Field Magnetic Induction

Short-range communication
• Low-interference
• High data integrity

Power Delivery

External processor of the CI supplies all of the implant power
• Majority of the battery power is used to run the implant itself
• The efficiency of the battery is impacted by the skin flap
thickness
• In other words, if someone’s skin is thicker, it could impact
the battery power of the unit

What is telemetry?

Bidirectional communication
• Allows impedance checks to occur
• Supports the ECAP measurements

Clinical Relevance of Telemetry

Telemetry confirms the electrode’s integrity
• Telemetry assists in troubleshooting
• Telemetry supports objective measures

Data Integrity and Checksums

Signals sent in packets with checksums
• The implant then verifies the accuracy of the information
• This helps prevent unintended stimulation

Summary of the Concept “Induction”

Induction enables wireless CI function
• Induction powers the CIs
• Induction transfers programming data safely and effectively

Resting Membrane Potential

Neuron interior ~ -70mV
• Maintained by ion gradients
• Creates readiness for firing

Biphasic Electrical Pulses

There are two phases: positive and negative
• Each have an equal charge in both phases
• The charges are short durations (microseconds)

Why Biphasic Pulses Matter?

It helps prevent charge buildup
• It protects the neural tissue
• It helps maintain physiological safety

Action Potentials

Sodium channels open up
• Rapid depolarization
• Electrical signal propagates

Pulse Parameters

Current amplitude
• Pulse width
• Interphase gap
• Interpulse gap

Current Amplitude

This is the height of the pulse
• It is measured in microamperes
• Increasing amplitude will increase the loudness

Pulse Width

Duration of each phase
• Increasing width increases the charges in the CI
• Used when compliance limits are reached

Electrical Charge

Charge = current x pulse width
• Primary determinant of loudness from the unit
• Two pulses can have equal charge via different parameters

Loudness Growth

Must normalize soft, conversational, AND loud sounds
• Think about this from a hearing aid perspective...
• Requires a careful balance of amplitude and width
• Each electrode has an individualized amount of loudness added
to it

Voltage Compliance

Maximum current limited by the voltage of the unit
• This is determined by impedance
• It cannot exceed the battery’s capacity

Compliance limits

This occurs when current cannot increase further
• This indicates loudness has plateaued
• This is most common in high-impedance electrodes

Managing Compliance

This increases pulse width
• It reduces stimulation rate if needed
• The battery capacity must be considered

Clinical Mapping Implications

This explains the “can’t get louder” complaints
• It predicts the potential mapping challenges
• It helps guides the audiologist when making programming
decisions

Electrode Anatomy

The electrode leads
• Intracochlear contacts
• Extracochlear ground electrodes

Intracochlear Contacts

Platinum-based contacts
• Each corresponds to one channel
• Apical portion = low-frequencies
• Basilar portion = high frequencies

Ground Electrodes:

Complete electrical circuit
• This is used for telemetry
• This is located INSIDE of the cochlea

Lateral Wall Arrays:

Positioned along the scala tympani wall
• Designed for atraumatic insertion
• Favors hearing preservation

Electrode Array Configurations

Lateral wall
• Perimodiolar
• Mid-modiolar

Perimodiolar array

• positioned near the modiolus

• requires less electrical current

• there is a higher risk of scalar translocation

Mid-modiolar arrays

• balance between proximity and safety

• limited outcome data available

• manufacturer-specific data

electrode length:

longer array= deeper insertion

angular depth is more meaningful than length

this influences frequency allocation

angular insertion depth

• full insertion depth = 450-630 degrees

• each manufacturer will have different philosophies on insertion depth

what are short arrays used for?

hearing preservation

cochlear number of contacts?

22

advanced bionics number of contacts?

16

MED EL number of contacts?

12

loudness=

charge, not volume

what are the pre activation procedures?

• Emphasizes that adjustments to the CI require time
• Establishes realistic expectations for benefit and performance
• Prepares recipients and families for varied initial responses to
sound
• Reviews programming schedule and postoperative time
commitments

Setting the State for CI Programming

• Initial programming should prioritize comfort and acceptance
• Early maps are intentionally conservative
• Patient responses guide gradual adjustments
• The programming environment should reduce stress and fatigue

what does the physical examination look like after CI surgery?

• assess surgical site and incision healing

• confirm absence of pain, swelling, or infection

• evaluate magnet site comfort and retention

• ensure medical readiness for activation and programming

what is streamlined programming?

uses fewer measurements to reduce fatigue

what is comprehensive programming?

involves a detailed assessment across electrodes

setting threshold levels for adults?

• Threshold (T) levels represent the lowest level of electrical
stimulation that produces auditory perception
• T-levels define the lower boundary of the electrical dynamic range
• Accurate T-levels ensure access to soft environmental and speech
sounds
• Adult recipients typically provide reliable behavioral responses

T-levels are typically measured using behavioral detection tasks
• Ascending stimulation is commonly used to identify first auditory
perception
• Measurements may be obtained on selected electrodes and
interpolated
• Clinical judgment is used to ensure comfort and consistency

Setting Threshold Levels for Children

• Behavioral responses may be limited or inconsistent
• Developmental level guides measurement approach
• Conditioning and observation are often required
• Threshold estimates may rely on conservative settings

Outline of the Hearts for Hearing Protocol for VRA in Children

• Protocol designed for programming young pediatric CI recipients
• Uses visual reinforcement to establish conditioned responses
• Emphasizes consistency, efficiency, and child engagement
• Adapted for children with limited behavioral reliability

• Establish a conditioned response using visual reinforcement
• Present electrical stimulation at suprathreshold levels
• Gradually decrease stimulation to estimate the threshold
• Repeat across selected electrodes to reduce fatigue

Additional Measures to ensure Adequate T-Levels and Confirm
Audibility

Use behavioral observations to confirm sound awareness
• Verify audibility using speech and environmental sounds
• Ling sounds can be used to confirm access to the speech spectrum
• Cross-check threshold settings for consistency across electrodes
• Adjust T levels if soft sounds are not reliably detected

T-levels =

detection

m or c levels=

comfortable loudness

M-levels define the _________ of the electrical dynamic range

upper boundary

Upper stimulation levels represent

maximum comfortable loudness (M-levels)

Evoked Stapedial Reflex Thresholds (ESRTs

ESRTs provide an objective estimate of upper stimulation levels
• Reflexes are elicited by electrical stimulation through the CI
• ESRTs often correlate with comfortable loudness levels (M-levels)
• Useful when behavioral loudness judgments are unreliable

Setting Upper-Stimulation Levels for Children

• Upper-stimulation levels represent comfortable loudness, not
detection
• Behavioral loudness judgments are often unreliable in children
• Developmental level strongly influences measurement approach
• Conservative upper levels are typically used initially

Upper levels may be estimated using observation and conditioning
• Objective measures can support upper-level estimation
• Gradual increases are made over time as tolerance improves
• Ongoing monitoring is essential to avoid overstimulation

Additional Considerations in the Measurement of Stimulation
Levels

• Patient attention and fatigue affect response reliability
• Loudness perception may vary across electrodes
• Session length should be balanced with data quality
• Clinical judgment is essential when responses are inconsistent

what is stimulation rate?

refers to the number of electrical pulses delivered per second

what does rate influence?

the temporal representation of sound

Pulse width

Refers to the duration of each electrical pulse
• Increasing pulse width increases charge delivery without increasing
current
• Useful when current limits or compliance issues are reached
• Changes in pulse width can affect temporal precision

what does channel gain adjust?

relative loudness across electrodes

why is channel gain used?

•Used to balance perception when some channels sound too soft or
loud
•Helps address variability due to neural survival or electrode position
•Adjustments are typically subtle and guided by patient feedback

Frequency Allocation

•Assigns acoustic frequency bands to electrodes
•Assumes correspondence between electrode position and cochlear
tonotopy
•Mismatch between frequency allocation and cochlear place can affect
pitch perception
•Adjustments may improve sound quality but require adaptation time

Limitations of Electrical Hearing Compared to Acoustic Hearing

•Normal hearing uses narrow auditory filters
•Electrical stimulation creates broad excitation
•Competing signals are harder to separate

The Complexities of Speech Acoustics

• Speech contains overlapping spectral and temporal cues
•Accurate perception requires fine frequency resolution
•Electrical stimulation limits cue separation

Complexity of Music and Environmental Sounds

• Music relies on fine pitch and harmonic structure
• Environmental sounds are acoustically variable and nonstationary
• Cochlear implants preserve rhythm but degrade timbre and pitch

Simultaneous Analog Stimulation (SAS)

• Early multi-channel analog coding strategy
• Continuous analog signals are delivered simultaneously
• Limited benefit due to channel interaction

Cochlear Implant Signal Coding Strategies

Convert acoustic sound into patterns of electrical stimulation
• Balance spectral resolution and temporal information
• Prioritize envelope cues for speech understanding

Feature Extraction Strategies

• Select perceptually important speech cues
• Emphasize temporal envelope information
• Reduce channel interaction and redundancy

MultiPEAK (MPeak) Signal Coding Strategy

• Feature extraction–based coding strategy
• Represents dominant spectral peaks over time
• Designed to improve speech cues beyond simple formant tracking

Continuous Interleaved Sampling (CIS)

• Pulsatile, non-simultaneous stimulation strategy
• Envelope extraction across multiple frequency bands
• Reduces channel interaction and improves speech clarity

Multiple Pulsatile Sampler (MPS)

•Pulsatile coding strategy derived from CIS
•Samples envelopes across multiple channels
•Increased stimulation efficiency with reduced interaction

Additional Variants of CIS

• Built on CIS principles with targeted refinements
• Modify pulse timing, rate, or channel selection
• Aim to improve efficiency and perceptual outcomes

HiResolution Sound Processing

• High-rate pulsatile stimulation strategy
• Emphasizes detailed temporal envelope representation
• Builds on CIS with increased stimulation rates

N-of-m Strategies

•Select most salient channels in each time frame
•Stimulate only a subset of available electrodes
•Improve efficiency while preserving key speech cues

Spectral Peak (SPEAK)

•Early n-of-m cochlear implant strategy
•Selects spectral peaks across channels
•Emphasizes spectral detail over temporal rate

Advanced Combination Encoder (ACE)

•Hybrid CIS + n-of-m strategy
•Selects spectral maxima with high-rate stimulation
•Widely used in modern cochlear implants

Fine-Structured Processing (FSP)

•Attempts to convey temporal fine structure cues
•Adds timing information to selected low-frequency channels
•Complements envelope-based stimulation

Channel Interaction Compensation (CIC)

•Addresses the overlap of electrical fields across electrodes
•Uses strategy- or map-based adjustments to reduce interaction
•Aims to improve spectral clarity and neural selectivity

MED-EL Philosophy – Structure-Preserving Design

•Emphasis on atraumatic insertion
•Goal: preserve residual acoustic hearing
•Designed for apical reach (low-frequency representation)

MED-EL Uniqueness

•Longer electrode arrays (e.g., 31–34 mm)
•Thin, flexible lateral wall designs
•Reduced insertion trauma → better neural survival

•Deeper apical insertion → access to <500 Hz regions
•Enables temporal coding strategies to be functionally relevant
•Better pitch and prosody potential

•Wider electrode spacing compared to some systems
•Reduced overlap by physical separation, not only software
•CIC is more effective when physical interaction is already minimized

AB’s Electrical Field Imaging (EFI) & Modeling

•Measures the spread of electrical current
•Evaluates the electrode–tissue interface
•Assesses channel interaction
•Detects irregular stimulation patterns
•Supports clinical troubleshooting

Advanced Bionics ClearVoice

•Built-in noise reduction feature
•Enhances speech in noise
•Reduces steady-state background noise
•Adjustable intensity levels
•Automatic environment detection

Setting Stimulation Levels - AB

•Establish T-levels (threshold)
•Establish M-levels (comfort)
•Define electrical dynamic range
•Ensure loudness balance across electrodes
•Adjust based on perception

Setting Stimulation Rate- AB

Pulses per second (pps)
•Influences temporal resolution
•Affects sound quality
•Impacts battery consumption
•Individual variability