Proefschrift_vd_Beek

Hearing is improved, but further improvement is desired Cochlear implantation has restored hearing for many patients, both adults and children. The quality of life of these patients has improved as a result of the new communication possibilities that arise from implantation. However, significant outcome variability persists; outcomes range from excellent results to minimal open set word recognition [Holden et al., 2013]. Even the best-performing patients experience difficulty hearing and understanding speech in noisy surroundings [Spahr and Dorman, 2005;Fetterman and Domico, 2002]. In addition, most patients experience limited music appreciation [McDermott, 2004]. Therefore, there is a continued strong desire for further improvements in cochlear implants. Technical limits are improvable Outcome limits are attributable to bothpatient factors and implant-related factors [Blamey et al., 2013;Holden et al., 2013]. Although biographical data can be used to help identify patients with proper indications for cochlear implantation and the candidacy criteria have been broadened, unfavorable biographical or audiological factors are not likely to be therapeutically altered in the near future. Improvements in cochlear implant outcomes are more likely to result from technical improvements in cochlear implants. The optimization of the different parts of the cochlear implants is an ongoing process. Although no significant leaps in progress have been made in recent years, any improvement represents a small step forward for (future) cochlear implant users. Microphone improvements The first step toward improving a patient’s perception of a signal transmitted by a cochlear implant to the patient’s auditory neurons involves improving the quality of the incoming signal. The most troublesome issue for cochlear implant patients is listening to speech signals in noisy surroundings [Spahr and Dorman, 2005;Fetterman and Domico, 2002]. Directional microphones can address this problem by transmitting the speech signal while attenuating background noise. Consistent with experiences with directional microphones in hearing aids, directional microphones in cochlear implants clearly result in improved speech understanding in noisy circumstances, including an improvement of up to 8 dB in speech reception thresholds (SRT) [Wouters and Vanden Berghe, 2001;Razza et al., 2013;van der Beek et al., 2007] [Chapter 2] . However, improvements in the quality of the incoming signal do not completely solve problems with hearing in noisy situations. After clinical tests with directional microphones were performed in our clinic, only a limited number of patients acquired a directional microphone despite the fact that all of the patients demonstrated clear improvements in the laboratory setting [Chapter 2] . Aesthetic issues may have played a role, as the external directional microphones used in the study by van der Beek et al. (2007) were rather large. However, the improvements obtained with directional microphones are relatively large compared with the 1-2 dB improvement in SRT obtained with more electrodes, higher rates [Friesen et al., 2001;Frijns et al., 2003] or bilateral cochlear implantation [Ricketts et al., 2006]. Although built- in directional microphones are used by cochlear implant patients in very limited circumstances, the microphones impart a clear added value in those circumstances [Mosnier et al., 2014]. Alternatively, noise reduction algorithms are used to

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