Electrophysiological and Psychophysical Measures of Amplitude Modulation Discrimination Interference in Cochlear Implant Users
* Presenting author
Cochlear implants (CIs) work by dividing the incoming acoustic signal into a limited number of frequency channels, extracting the slowly varying amplitude envelope in each channel, and using this to modulate the level of electrical pulses delivered to the auditory nerve fibres. The amplitude modulation (AM) cues that are transmitted are crucial for speech understanding. The use of AM cues can be affected by interference from adjacent channels caused by current spread, which can be further exacerbated if traumatic electrode placement or poor neural survival occurs. We have tested twelve adult CI users with a measure of across-channel modulation interference (AMCI). The discrimination of different rates of AM in the presence of interfering AM on adjacent channels is measured behaviourally and via the electrically-evoked auditory change complex (eACC), a cortical potential that occurs in response to a change in an ongoing stimulus, AM-rate change in this case. The ability to discriminate AM rate (based on behavioural measures and eACC) will be compared to speech perception scores. If the eACC to AM rate changes proves to be reliable, it can be used with children and also to identify poorly discriminated CI electrodes, to guide re-mapping.