Ear prostheses Flashcards
Place coding of sound in the auditory cortex
Neurons respond anteriorly to low frequencies, and high frequencies more towards the back of the auditory cortex.
For higher frequencies, the place code is valid, but not the ____ coding for individual neurons
Time
Brain stem recording
- playing a word e.g. ‘car’
- The brain signal was ran through an audio device to know the sound of electricity in the brain
- Above the chance level, participants could say that the electrical brain sound sounded like the word ‘car’
Brain stem recording :
- playing pure tone
Time code of pure tone, frequency of response matches the frequency of the time wave
Tonal audiometry
measuring the level of hearing ability
Audiogram
Minimal volume needed to hear a sound
- For normal hearing : you can hear every frequency with nearly 0dB
- With mild to moderate hearing loss : you need more dB (40-50dB) to hear sounds, which is missing most speech content
Measure of speech understanding and hearing
Measure the percentage of speech that someone can repeat
2 types of devices to help hearing loss
- Hearing aids
- Cochlear implants (for more severe hearing loss)
Hearing aid design
- Sound amplifiers : microphone that picks up sound in the environment and processor that makes it louder in the ear
Behind-the-ear (BTE) hearing aid
- Microphone and electronic chip sitting behind the ear
- Loud speaker inside the ear
In-the-ear (ITE) hearing aid
- Block the ear with the device and processing chip
- Not always the best solution because creates occlusion
Hearing aids and programming software
Knobs on the programming software increase the volume or the acoustic gain for the specific frequencies that need more volume, creating a gain curve
Hearing aid fit check : Validation of acoustic output at the tympanic membrane
With a computer
- Increase the volume on the device
- Check with a probe microphone located at the eardrum to validate that the volume that is being delivering there is indeed what is prescribed.
Directional microphones
Allow to focus on speech
Noise-cancelling algorithms
Cancel background noise
True or false : there are prescription hearing aids and Over-the-counter (OTC) hearing aids
True
Cochlear implant
- An external microphone picks up sounds from the environments, transduces them into a firing pattern, and transmits them to the magnet on the skull
- The signal is then sent to the implant under the skin, which sends it along the electrode in the cochlea
- The electrode with many stimulation points shoot electricity on the nerve along the basilar membrane of the cochlea (from base to apex)
Candidacy for cochlear implant
> 60 dB of hearing loss
< 60% of speech recognition
Can we combine cochlear implants and hearing aids ?
Yes
Example :
Mild hearing loss at 500Hz, but complete hearing loss starting at 1500Hz
Solution :
- Hearing aid for low frequencies
- Cochlear implant for high frequencies
Electro-acoustic stimulation (EAS)
Low pitches : acoustic stimulation of loudspeaker
- Will go through natural pathway of sound, but amplify with a loud speaker inside the ear to fix the mild hearing loss at these frequencies
- The sound will go where the low frequencies are place coded : at the apex of the cochlea
High pitches: electric stimulation of cochlear implant
- Insert electrode inside the ear, and send electricity right on the nerve to restore hearing
Profound sensorineural hearing loss
Equivalent to not hearing anything at all
E.g. does not hear anything below 85-90dB and can only repeat 10% of 100dB speech
Maximal cochlear duct coverage improves sound _____
Quality
High pitch sounds and cochlear implants
Just after activation of the cochlear implant, people report more high-pitched sound because the cochlear implant transfers sounds only at the entrance of the cochlea where the high pitched sounds on the nerve are coded.
Later, people do not report hearing high pitched sounds because they got used to the cochlear implant.
Anatomy-based fitting
- Using CT scan to locate the electrode
- Trying to match the frequencies that we send to the electrodes to match them to what the hearing nerve is meant to hear at the particular location
Folding of cochlear implant in left ear with a place coding that’s meant to fit the whole cochlea will create …
mismatch between left and right ear
Solution to folded cochlear implant in one ear
Solution : ABF to trade off a full delivery of sounds (cut off base sounds) for a match across both ears
ABF improves … in experienced bilateral CI users
speech recognition in quiet and in noise
Hearing handicaps in single-sided deafness
- Recognition deficit for speech signal in the ipsilesional auditory hemifield for the dead ear side
- Speech-in-noise recognition deficit
- Sound localization deficit
Pupillometric measure of listening effort : pupil dilates with higher cognitive effort
ABF improves speech recognition … in experienced CI users with single-sided deafness (Kurz et al., 2024)
in noise, but not in quiet,
ABF improves speech-in-quiet recognition in patients newly implanted with a …
unilateral EAS CI
A proper place coding does good only for patients with…
a reference (either another healthy ear or normal hearing inside the ear beside the cochlear implant)
Does not help in bilaterally deaf patents newly using a unilateral CI
Anatomy-based fitting improves _____ perception in bilaterally deaf patients using a unilateral CI
Music
- Subjective quality rating of music samples
- Melodic contour identification
- Familiar song appreciation
There is time coding only for the low pitch sounds at the ____
Apex
Continuous interleaved sampling (CIS)
All neurons with a cochlear implants will fire with a steady electric pulse rate, and depending on the intensity of acoustic waves, the voltage will increase and decrease.
Fine temporal structure processing (FSP)
More moderns approaches of coding the sound will make sure the signal sticks to the temporal architecture of the wave inside the envelope of the sound signal.
FSP fails to improve … in bilateral deaf patients with a newly-implanted or experienced unilateral CI
- speech recognition in quiet or in noise
- melody discrimination
introduction of unilateral acoustic input in unilateral CI users (EAS) improves …
speech recognition in quiet and in noise
Fine structure processing improves _____ perception in experienced unilateral and bilateral CI users
Music
- Improved detection of filtered low frequencies
Tinnitus
With hearing loss, the nerve receives less stimulation, but a compensatory mechanism from the cochlear nucleus in the brain stem to the auditory cortex is going to increase the volume in the brain.
When we fix someone’s hearing loss, do we also fix their tinnitus ?
Yes, Tinnitus level is measured with Tinnitus Handicap Inventory (THI) (from 0 to 100) and it decreases with cochlear implant
