Acoustic models of consonant recognition in cochlear implant users

Verschuur, Carl (2007) Acoustic models of consonant recognition in cochlear implant users. University of Southampton, Institute of Sound and Vibration Research, Doctoral Thesis , 271pp.


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Normal-hearing adults have no difficulty in recognising consonants accurately, even
in moderately adverse listening conditions. By contrast, users of multichannel
cochlear implants have difficulty with the accurate perception of consonants, even in
good listening conditions. Cochlear implant users are known to show systematic
deficits in recognition of consonant features, with perception of the place feature,
which relies on spectral information, being worst. These deficits may be attributed
both to signal distortions introduced by the processing of the implants and to other
factors, in particular the spectrotemporal distortions which occur at the interface
between electrode array and auditory nervous system, including cross-channel
interaction. The objective of the work reported here was to attempt to partial out the
relative contribution of these different factors to consonant recognition. This was
achieved by comparing cochlear implant users’ perceptual errors, analysed in terms of
information transmission, with errors made by normal-hearing subjects listening to
acoustic models of implant processing, in various conditions.
Two initial experiments were undertaken to develop and refine an acoustic model of
the Nucleus 24 cochlear implant. Findings from these two experiments informed the
design of the main acoustic model experiment, which was undertaken in parallel with
a further experiment involving users of the Nucleus 24 device. In both experiments,
subjects listened to nonsense syllables with and without the addition of stationary
background noise, in three different configurations of implant processing parameters.
Additionally, in the acoustic model experiment, a simulation of cross-channel spread
of excitation, or “channel interaction”, was varied. Results showed that acoustic
model experiments were predictive of the pattern of consonant feature transmission in
cochlear implant users with better baseline consonant recognition scores. Deficits in
consonant recognition in this subgroup could be explained by the loss of
phonemically relevant acoustic information in speech due to the nature of cochlear
implant processing, while channel interaction appeared to play a smaller role in
accounting for problems in consonant recognition. The work also evaluated the effect
of changes in channel number and stimulation rate and failed to find any changes in
consonant recognition as these parameters were varied. The lack of a stimulation rate
effect was consistent with acoustic measurements of the temporal modulation transfer
function of the processor, which showed almost no change across stimulation rates.

Item Type: Thesis (Doctoral)
Subjects: R Medicine > RF Otorhinolaryngology
T Technology > TA Engineering (General). Civil engineering (General)
Divisions : University Structure - Pre August 2011 > Institute of Sound and Vibration Research > Human Sciences
ePrint ID: 51152
Accepted Date and Publication Date:
March 2007Made publicly available
Date Deposited: 07 May 2008
Last Modified: 31 Mar 2016 12:29

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