hearing implants Flashcards
Who are suitable candidates for cochlear implants
Congenitally deaf children (ear don’t grow)
Victims of meningitis
RECENTLY deafened adults
Have to be super mega deaf to be a candidate
Electrodes in implant
Up to 22 depending on model
Electrodes trigger different areas
Tries to give different frequencies to different areas
Cochlear design and how it fits in
Forced around the cochlear underneath the vascular membrane
Allows us to achieve different frequencies due to amount of contact electrode has across the cochlear
Ganglion cells spaced out neatly to allow for separate excitement of cells
How does cochlear implant work
Sound processor sends information to internal implant which sends information to electrode which sends info to hearing nerve to allow for action potential
Phase locking in cochlear implants
Variation in pressure is not used
Fine structure of the amplitude is not used as you can’t get full range of frequencies
If we added in finer structure than people with cochlear implants would be able to hear better
No time delay so they rely on interaural level differences to tell where sound is coming
One stimulation at a time for clearer sound
Uses a pulse system, making each pulse proportionate to how much sound is in the channel
Variation in amplitude change is taken and that is the information communicated
Noise vocoding
Follows envelope changes
Multiple channels of the vocoder help make perceiving what it is saying even clearer
Continuous interleaved sampling
CIS strategy involves taking an envelope and using pulses that vary in size in accordance to envelope
Insertion depth problem
Speech recognition declines with insertion depth if speech information is only delivered to the correct position in the cochlear
Input will go in even if the frequency isn’t stimulated in the right place
Faulkner (2003) - Frequencies lost + Mickey Mouse voices
Frequencies below 1500Hz lost entirely but stimulated naturally
Lower tones lost as electrode not going in far enough
400Hz being modulated at 1500Hz leads to Mickey Mouse sounding voices
Speech in noise problem
The less channels there are, with background noise speech is hard to understand
Threshold for understanding goes up
Probably to do with loss of phase locking
Current spread problem
Eventually will plateau in your performance
Electrode won’t always be right next to ganglion cell so you can get interference
Cardiff developed a vocoder that can represent current spread
Benefits of a short electrode
Can get to high electrodes very easily
Helps people who can’t hear high frequencies
Normally functioning frequencies survive even with cochlear implant
Ethical issues with Turner (2004) experiements
Using humans with hearing loss… kinda bad.
Backed up by using vocoder though!
Combination of acoustic and electric hearing helps
Benefits of bilateral implants for speech perception in noise
Improvements in speech recognition threshold when target and interference were separated in space but improvement only reflects better ear listening
