Introduction to Cochlear Implants and Candidacy Issues
Alice E. Holmes, Ph.D. Professor University of Florida
Cochlear Implant
A device that electrically stimulates the auditory nerve of patients with severe-toprofound hearing loss to provide them with sound and speech information.
Types of Devices
Position
Extra-cochlear Intra-cochlear
Electrodes
Single channel Multi-channel
Technical and Safety Issues
Intra cochlear electrodes better Problems with channel interactions Transcutaneous versus percutaneous
Technical and Safety Issues
Channels
Studies show correlation between speech perception and number of electrodes in use Need to select the electrodes transmitting the most useful information
Allow pattern of electrodes to be altered in presence of reduced neural populations or spread of current to facial nerve
Technical and Safety Issues
Magnetic Resonance Imaging Surgical issues
New Freedom
Med El Pulsar
Advanced Bionics System
Auditory Brainstem Implant
Approved October 20, 2000 Uses the Nucleus 24 system processors Plate array with 21 electrodes
Worldwide
Over 100,000 multi-channel implants
University of Florida Cochlear Implant Program
Implanted our first patient in 1985 Currently follow over 400 cochlear patients
Who is a candidate?
Severe-to profound sensorineural hearing loss Hearing loss did not reach severe-to-profound level until after acquiring oral speech and language skills Limited benefit from hearing aids
Who is an adult candidate?
< 50% aided speech recognition on recorded sentence material in the ear to be implanted < 60% aided speech recognition on recorded sentence material in the un-implanted ear
Speech Processing Strategies
Originated from auditory neurophysiological, psychophysical and speech science Evaluation of speech processing schemes provides understanding of how responses to electrical simulation differ from those of sound
Single Channel (Electrode) Strategies
Initially simple to engineer Assumed brain would find important info for hearing speech 3M/House device
Filtered signal over frequency range 200- 4000 Hz – nonlinear modulation of a 16K Hz carrier wave
Provided users with info on speech boundaries and stress
Insufficient information to discriminate formants and their transitions No open set word recognition
Multi-Channel Strategies
Fixed filter strategies
Unsatisfactory results due to simultaneous stimulation of electrodes leading to channel interaction Overlapping electrical fields
Unpredictable loudness variation Lead to principle of presenting electrical stimuli non simultaneously
Multi-Channel Strategies
Interleaved pulsatile strategy
Fixed filter system – non simultaneous interleaved pulses Reduce channel interaction Benefited those with poor nerve survival Performance improved as number of channels increased
F0/F2, F0/F1/F2, Multipeak and SPEAK
Multi-Channel Strategies
Continuous Interleaved Sampling (CIS)
Evolved from fixed filter scheme that used IP to avoid channel interaction Higher pulse rate – better representation of voicing information Outputs of 6 or more filters sampled and used to stimulate the same number of electrodes on a place coding basis Uses biphasic pulses rather than analog
Multi-Channel Strategies
Advanced Combined Encoder(ACE)
Combines SPEAK & CIS Up to 14,400 pps
High rate ACE (up to 34,000 pps)
ACE (RE)
Outcomes for Post-lingual Adults
Wide range of success Most score 90-100% on AV sentence materials Majority score > 80% on high context Performance more varied on single word tests
Health Utility Changes
Profound Hearing loss results in a decrease from 0.36 to 0.63 Cochlear implantation results in an increase from 0.07 to 0.41
Outcomes for Post-lingual Adults
Top 30 % function fairly well on the telephone Bottom 30 % avoid the phone The rest use the phone with significant others or only when necessary