Summary and conclusions: current fitting methods

This document does not intend to give an opinion on which fitting method is best, the idea of this document is to summarize the available ideas so the reader can have an informed opinion and is pointed to locations for further study. However there are a few general remarks we can make in summary.

There are a lot of different fitting options and none of them have proven to be superior in terms of performance (not even classical ‘all-electrode’ fitting). For setting T and C levels, live fitting methods seem to hold the biggest promise since they are quick and use a realistic signal for fitting. The combined data point towards the fact that for a group the exact setting of T-levels are not all that important and that individual electrode psychophysics testing is not per se better than any other method. Anecdotal evidence however, does indicate that for some individuals a precise setting of T and C levels can be important. There seems to be no obvious indicator at the moment to which recipients need manual fitting and which can be helped with fast fitting methods. This is an important research field for the future. There is no conclusive answer to the question whether or not using an NRT profile creates a better map, however, NRT certainly has its value in fitting since it can give guidance for initial map setting. Only one method has been tried so far (to my knowledge) that optimises parameters other than T and C levels. This genetic optimisation method may prove to be useful but we need more data to conclude this.

There seems to be some merit in self-fitting but it seems unlikely that we can ever create the perfect map from objective measures only; interaction with the recipients will remain needed.

Identified needs for new fitting methods

 
Two interrelated recent developments in the CI field raise the need for additional approaches to fitting. These are A) the increasing use of two bilateral cochlear implants (e.g., Long et al., 2003; Muller et al., 2002; Nopp et al., 2004; Tyler et al, 2002) and B) a major increase in interest in the combined use of a cochlear implant with a contralateral or ipsilateral acoustic hearing aid (e.g., Ching et al., 2001, Ching et al., 2004, Hamzavi et al., 2004). The main challenge of these developments for fitting is to ensure that the implant user can effectively combine and integrate information from the two prostheses. One promising approach to a more optimal combination of information from two prostheses is to develop a more complete understanding of the effects of any mismatching of acoustic frequency to cochlear place mapping between two prostheses. Even with a single cochlear implant it is clear that acoustic frequency to cochlear place mapping can have major effects on benefit (e.g., Fu and Shannon, 1999, 2002; Shannon, Zeng & Wygonski, 1999). However these effects appear to be substantially reduced with experience (Rosen, Faulkner and Wilkinson, 1999). The importance of mismatches between two ears, with either two bilateral implants or with an implant combined with a bilateral hearing aid, is little understood and merits investigation.

Synergies in fitting methods for cochlear implants and hearing aids

As the joint fitting of cochlear implants and acoustic hearing aids becomes more common, it is likely that fitting approaches for these two classes of prosthesis will become more closely linked. This seems especially likely in the use of perceptual testing methods (e.g. speech reception in noise) in the fine-tuning of prostheses.
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