Abstract:
Music perception in cochlear implant (CI) listeners has been found to be generally unsatisfactory.
An improved understanding of music perception in CIs is thus required, where research
into the perception of timbre, an important aspect of music, could assist in improving this
knowledge base. The aim of this study was to determine what underlies measured timbre
perception in cochlear implantees. This was investigated by means of an experimental component
and the development of a model of timbre perception in the electrically stimulated
auditory system. Timbre perception was first measured in five normal-hearing (NH) and five
CI listeners by means of three important timbre features, namely the spectral centroid, the
logarithm of the rise time and the spectral irregularity. Discriminations of synthesised tones
where these features were independently varied revealed that CI listeners had substantially
larger threshold values than NH listeners for each of the timbre features investigated. Confusions
of musical instrument timbres were also determined in five CI and five NH listeners
by similarity ratings of original and acoustic simulations of musical instrument timbres, respectively.
An acoustic model based on a six-channel advanced combination encoder (ACE)
processor was developed in order to process 10 musical instrument timbres. The results of
the similarity ratings revealed differences in the information conveyed through the timbre
features for NH and CI listeners, and indicated that the acoustic model did not accurately represent timbre in the electrically stimulated auditory system, but provided reasonable measurable
results which could be compared to timbre perception model predictions. A model of
timbre perception was developed by combining the results of the discrimination tasks with
signal detection theory, in an attempt to predict the amount of information conveyed through
each of the timbre features to both NH and CI listeners. The model was found to predict
the experimental results obtained from the similarity ratings for both NH and CI listeners
acceptably for each of the three timbre features. This outcome also confirmed the validity of
the choice of the three timbre features as the primary features contributing to timbre perception,
implying that timbre perception through a CI would be improved if CI processors could
be optimised for the transmission of these three important timbre perception features. The
model of timbre perception therefore has application in advancing CI research to facilitate
music perception in the electrically stimulated auditory system.
