Understanding why a proportion of adults with a cochlear implant do not understand speech well
The degree of benefit gained from hearing aids and cochlear implants varies widely across users. Unfortunately, a proportion of cochlear implant users cannot understand speech with their device unless they combine it with lip reading. While much of the variability in speech understanding is accounted for by factors such as the duration of deafness and experience with the device, a significant portion of the variability amongst cochlear implant users remains unexplained.
Our goal is to understand why some people do not understand speech with a cochlear implant as well as other people. With this knowledge we aim to determine the optimal cochlear implant processing features and hearing therapies for each person after they get their implant, so that the benefit from their implant is maximised.
There are three main mechanisms that have been associated with poor benefit from a cochlear implant. First, the remaining auditory nerves in the cochlea may be sparse or have gaps where there are no nerve cells; secondly, the ability of a person to perceive the differences in intensity at different frequencies in a sound may be compromised; and thirdly, the speech understanding networks in the cerebral cortex may have been compromised by plastic changes due to periods of deafness.
In this project, we are following adults with a new implant over the first two years of their experience. Soon after implantation, we are testing each person diagnostically for each of the three potential mechanisms mentioned above, and relating what we find to how well they develop speech understanding over the first 12 months of implant use. We will then pilot different optimisation strategies that aim to overcome each individual’s predicted cause of poor speech understanding. The diagnostic methods include psychophysical and electrophysiological methods, as well as functional near-infrared spectroscopy.
Principal investigator – Professor Colette McKay
Team members – Dr Robert Luke, Ms Nicola Horvath
NHMRC; The Garnett Passe and Rodney Williams Memorial Foundation; Lions; Pierce Armstrong Trust; Melbourne Neuroscience Institute seed funding; and veski Senior Innovation Fellowship (2013-2016) to Prof McKay.