Cochlear implants (CIs) enable many deaf or severely hard-of-hearing people to understand speech again. However, the results vary greatly: while some people can understand almost everything, others have difficulty, especially in noisy environments such as parties or busy streets. This thesis investigates why these differences exist and how the adjustment of the CI can be improved. To this end, new measurement methods have been developed that are objective and reliable, independent of language or personal preference. We measured how well signals from the implant reach the auditory nerve and how the brain processes these signals. Both reaction time measurements and EEG were used for this purpose. A special app was also developed, which participants could use to test themselves in the laboratory and at home. The results show that four factors contribute approximately equally to differences in speech comprehension: processor settings, electrode-auditory nerve transmission, processing in the brain and cognitive skills. The new methods make it easier to identify the problem for each CI user. Testing at home also makes it possible to monitor users over the long term and collect data on a large scale. This brings us closer to a more personalised adjustment of the implant, with the aim of improving speech comprehension, especially in difficult listening situations.
Elisabeth studied physics and worked in product development at Philips and later ASML. In 2000, she started her own company in web design and custom software for small and medium-sized businesses, with applications in knowledge management, communication and sales. In 2014, she took courses in the Master's programme in Neuroscience at Radboud University. She then began her PhD research, working four days a week alongside her business, at the Biophysics Department of the Donders Centre for Neuroscience. She is currently a postdoctoral researcher there in the follow-up project OtoControl 2, in which the developed measurement methods are being tested on approximately 120 CI users in three countries.