Cochlear implants have restored hearing to more than 300,000 people world-wide. They do so by electrically stimulating the auditory (hearing) nerve using an array of electrodes implanted into the cochlea (inner ear), acting in place of the damaged sound-sensing hair cells. Each electrode conveys information about a specific range of frequencies (pitches) of sound, similar to how different hair cells transmit information about sounds of different frequencies. However, there are over 15,000 hair cells in the average human inner ear, each responding to a slightly different frequency, and only 20 electrodes at most in a cochlear implant – as a result, listening through an implant sounds very different to natural hearing.
Although many cochlear implant users can understand speech well in quiet situations, a minority do not, and even the most successful users struggle in noisy situations. Although many different methods for improving speech perception through a cochlear implant have been tried, the results have been quite variable; often a particular method will make things better for some people but worse for others, making it hard to develop ways to improve listening through an implant for all users.
This research project has two main aims. The first is to develop simple listening tests that will tell a clinician which electrodes lie in healthy regions of abundant auditory nerve survival within the inner ear, and which lie in so-called "dead regions", where the auditory nerve cells have died off, and there is nothing for the electrodes to stimulate. The researchers will test whether this knowledge can be used to turn off or re-programme “bad” electrodes (in “dead regions”), to see if this causes an overall improvement in speech perception for the listener.
The second aim stems from the idea that even if – as is often the case for existing methods – no single technique works for everyone, a person’s ability to understand speech can still be improved if their implant is programmed in the way that works best for them. The researchers will investigate whether a quick and simple listening test, using non-speech sounds, can quickly tell a clinician whether a new implant programming strategy will help or hinder a particular user, greatly speeding up and simplifying the process of developing bespoke programmes for cochlear implant users.
The results from this project should help to improve programming of cochlear implants for individual users, so that they can benefit more quickly from their implants.