Loudness and speech changes in cochlear implant listeners
Research type
Research Study
Full title
Post-activation changes in loudness and speech perception in Cochlear Implant Listeners
IRAS ID
301813
Contact name
Manohar Bance
Contact email
Sponsor organisation
Cambridge University Hospital NHS Foundation Trust+University of Cambridge
Duration of Study in the UK
3 years, 0 months, 0 days
Research summary
Cochlear implants (CIs) restore hearing to deaf people by electrically stimulating the auditory nerve. When the implant is first turned on, many patients report that everything sounds strange and hard to understand. After several months, though, speech perception becomes much easier. Interestingly, we do not know why this is. Part of the improvement is undoubtedly due to the person learning what speech sounds like through their CI. However we know from animal experiments that, when hearing is restored by a CI following long periods of deafness, there are lots of changes in the way the brain processes sounds. We plan to find out whether such changes occur in humans, and, if so, whether they contribute to the improvements in speech perception during the first few months of CI use. To do so we will perform some behavioural and EEG tests to see whether the brain gets better at analysing non-speech sounds, for which the “speech learning” is unlikely to occur. The results may be useful, for example, in understanding why a particular patient’s speech perception is not improving over time, and will also give us important new information on how the brain adapts to hearing again after a period of deafness.
Another huge change that occurs during the first few months is that sounds become softer, requiring the audiologist to turn up the stimulation current so that they are loud enough again. These changes are very large, corresponding to about one third of the difference between the softest sound one can hear and a loud sound. Surprisingly, we do not know where in the brain these changes occur. We will find this out by using a range of electrophysiological methods - such as EEG recorded from electrodes on the scalp - that measure neural activity in different parts of the brain. This will also allow us to develop a good objective measure of loudness changes, which could in future be used for example when adjusting the stimulus level in children or in adults who cannot make reliable verbal reports of loudness. We will also study another type of loudness change which occurs in some patients for whom the current level is turned up so high (in order to get a sufficiently loud sound) as to produce non-auditory sensations, such as facial twitches. This can be so bad as to prevent the patient from using their CI. We have found that turning the CI off for a few weeks allows the patients to hear sounds again at a lower current level that does not produce unwanted sensations. We will find out, using a larger sample, how many patients this works for, the time course of the change, and the stage of neural processing at which it occurs. Again, this may help patients by providing a reliable and objective measure of loudness changes, as well as telling us how likely the intervention is to work and how long a break we should ask patients to take.REC name
London - Brent Research Ethics Committee
REC reference
21/PR/1517
Date of REC Opinion
9 Nov 2021
REC opinion
Favourable Opinion