Perception of speakers vocal characteristics through cochlear implants

Cochlear-implants (CIs), by stimulating electrically the auditory nerve fibres,
can restore close to normal speech comprehension in most deaf patients,.
However, CIs only allow good speech intelligibility in quiet environments and
listeners* performance dramatically drops in noisy situations. When a
normal-hearing (NH) listener is confronted with a number of speakers talking at
the same time, they can use the perceived vocal characteristics of the speakers
(such as the voice pitch or vocal tract length) to identify and segregate the
competing speech streams. Unfortunately, some of the acoustic cues carrying the
vocal characteristics are not properly transmitted by the implant. This is the
case, for instance, for voice pitch, which is discarded due to the limitations
of the implant, essentially at the electrode-nerve interface. This deficit
partially explains the difficulty CI listeners have to understand speech in
noise. However, some other vocal characteristics, such as the vocal-tract
length of the speaker, are likely to be better preserved in the implant signal
processing. This vocal characteristic determines to a large extent the
perceived size of the speaker and is crucial for speaker discrimination.
Despite their importance, it is not known if these acoustic cues could be
transmitted through the CIs and be effectively used by CI users to improve
speech perception in noise. We will, therefore for the first time, conduct a
systematic study of the perception of this speech dimension in CI users. Better
understanding of how vocal characteristics are perceived by CI recipients will
allow improving speech enhancement strategies in the implant processors, which
will help to increase the intelligibility of speech in adverse situations by CI
users.

The main goal of the study is to characterize the perception of vocal
characteristics through a cochlear implant. It will span a number of aspects:
psychophysical characterisation, its relation to speaker discrimination, its
relation to single voice intelligibility, and its relation to competing voices
segregation. The study focuses primarily on vocal-tract length (VTL) but
another principal voice characteristic, glottal-pulse rate (GPR), will also be
manipulated. The proposed project consists of 9 experiments spreading to 3
years.

The study is an observational study, with both within-subject and across-group
comparisons. In all experiments of the study, a measurement variable is
collected as a function of VTL (and GPR), manipulated parametrically. The
subjects are presented with auditory stimuli and given a behavioural task. They
then have to make a judgement and have to provide an answer on a computer
screen. Thus, the measurement variables will be, in different experiments:
percent-correct discrimination and percent-correct identification.

There is no known risk, nor benefit associated with participation. The test
session will last for a maximum of 3 hours per listener, including breaks.
Session duration can easily be accommodated on the request of the participant
as needed. The sound level will always be adjusted to a comfortable listening
level for the participant.