This is a PhD studentship being carried out by Faizah Mushtaq in the laboratory of Dr Doug Hartley at the NIHR (National Institute for Hearing Research) Nottingham Hearing Biomedical Research Unit. Faizah began work in October 2016 and the project will finish in September 2019. This project is being jointly funded with Cochlear Ltd.
Cochlear implants change lives. They enable profoundly deaf children and adults to hear by converting sound into electrical signals that excite the hearing nerve, via implanted electrodes in the inner ear. These nerve signals are then transmitted to the brain to be heard as sounds.
While the majority of deaf children who receive a cochlear implant (CI) do benefit, how they then understand speech varies widely. A long period of deafness before surgery is often associated with poor speech performance post-implant, but young children with remarkably similar hearing capabilities can have different levels of understanding of speech. For example, some children who receive an implant after a number of years of deafness demonstrate excellent speech understanding, but the majority do not.
Right now, clinicians lack the tools they need to predict who will be able to understand speech well following cochlear implantation, and who won't.
The usual gold standard form of imaging that we use to visualise what is happening in the brain, functional Magnetic Resonance Imaging (fMRI), cannot be used with cochlear implants. So Faizah is investigating whether a technique called ‘functional near infra-red spectroscopy’ (fNIRS) can be used instead, to predict how well a child understands speech.
She and her colleagues in Dr Hartley's lab will measure children's brain activation, using fNIRS, while they are listening to speech – and to speech that has been 'time reversed' (time-reversed speech contains many of the same characteristics of speech but cannot be understood and is processed differently in the brain).
Evidence from brain imaging studies using fNIRS suggests that infants show more brain activity in the left side of their brain when listening to speech, compared to the same sound played backwards. By comparing the level of activation in the two sides of the brain, Faizah and her colleagues hope to find a way to measure whether a child is developing the ability to process speech sounds shortly after receiving a cochlear implant.
At the moment, and quite unexpectedly, many children who receive cochlear implants fail to achieve the level of speech understanding that clinicians predict (based on factors such as how long they've been deaf and how old they are at the time of the operation). We hope that Faizah's work will lead to the earlier detection of poor speech outcomes. This will help clinicians direct valuable rehabilitation resources to the right children – and help in counselling parents about what to expect following the implantation.