The aim of this thesis was to develop new speech coding strategies for cochlear implants (CIs) that improve the quality of the incoming sound. To implement a new speech coding strategy, often... Show moreThe aim of this thesis was to develop new speech coding strategies for cochlear implants (CIs) that improve the quality of the incoming sound. To implement a new speech coding strategy, often multiple components are adjusted without knowing the effect of these individual factors. Our research showed that the replacement of bandpass filters for more efficient filters, based on Fast Fourier transformation, has no effect on the performance of CI users. The FFT filters can therefore be implemented without problems.In this PhD research, the Dynamic Current Focusing (DCF) strategy was developed that leads to a narrower intra-cochlear electric field, especially at low loudness. This causes an improved spectral resolution and possibly also a better speech understanding in the long term. The studies in this dissertation showed that psychophysical tests, which are frequently used to evaluate new strategies, show learning effects, complicating the interpretation of results.Phantom stimulation is a strategy that results in a shift of the stimulated area. When applied to the most apical electrode contact it can be used to transmit lower tones than currently possible. This dissertation shows that the perceived pitch can be shifted 0.92 electrodes on average. Show less
Cochlear implants (CI) have proved to be a successful treatment for severely and profoundly deaf individuals. There is general agreement that the improvement of speech perception results has been... Show moreCochlear implants (CI) have proved to be a successful treatment for severely and profoundly deaf individuals. There is general agreement that the improvement of speech perception results has been due to ongoing development in CI electrode-array design, new speech processing strategies and by implanting patients with increasing amounts of residual hearing. However, although speech perception scores are very important indicators, there may be other outcomes that give essential information on the benefits of modern CI as outlined in this thesis. By assessing Quality of Life questionnaires and utilities before and after implantation, general health status and cost-utility were evaluated in pre- and postlingually deafened adult populations. In spite of the good results, it was realized that there was still room for improvement. Therefore, a high-rate speech processing strategy was investigated, which gave evidence of further improvement of speech perception performance (especially in noise), provided that the optimum number of electrodes was determined for each patient individually. These data suggested that objective individual parameter selection is obligatory to increase performance. For this purpose, we explored and used objective measures in an experimental and clinical setting to obtain basic knowledge about the electrode-nerve interface and, finally, to optimize individual implant function Show less
Cochlear implants (CI) are by now an accepted form of rehabilitation for profoundly deaf patients. CI users regain part of their hearing by direct electrical stimulation of the auditory nerve. With... Show moreCochlear implants (CI) are by now an accepted form of rehabilitation for profoundly deaf patients. CI users regain part of their hearing by direct electrical stimulation of the auditory nerve. With modern cochlear implants most users are able to achieve open-set speech understanding and are able to use the telephone. There are, however, still a lot of unanswered questions regarding the optimal design, stimulation paradigms, fitting methods and objective measurements. With the development of a realistic computer model of the implanted cochlea, as described in this thesis, these questions are analyzed from a fundamental perspective. This realistic model enables the analysis of clinical devices and gives insight in discrepancies between human and animal results. Insights gained from the model are used to improve clinical practice. Based on the model outcomes presented the characteristics of an improved electrode design were defined, and finally tested in a temporal bone study. Show less
