gms | German Medical Science

76th Annual Meeting of the German Society of Oto-Rhino-Laryngology, Head and Neck Surgery

German Society of Oto-Rhino-Laryngology, Head and Neck Surgery

04.05. - 08.05.2005, Erfurt

Fitting of cochlear implant processors by scaling of electric and acoustic stimuli

Meeting Abstract

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Deutsche Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie. 76. Jahresversammlung der Deutschen Gesellschaft für Hals-Nasen-Ohren-Heilkunde, Kopf- und Hals-Chirurgie e.V.. Erfurt, 04.-08.05.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05hno558

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Published: September 22, 2005

© 2005 Hoth.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.



Background: In all cochlear implant systems (CI), the transformation of acoustic sound intensity in electric stimulus strength is based on a mapping function which may be fitted to the needs of the CI recipient by the audiologist. Unfortunately, however, no valid algorithm is available for the selection of the optimal mapping parameters. In the present work, a procedure for the derivation of these parameters is described.

Method: Subjective categorical loudness scaling of electric and acoustic stimuli has been performed in 15 recipients equipped with nucleus (CI22 and CI24) or Med-El (C40 and C40+) systems in order to explore the benefit of loudness scaling for CI fitting and to achieve a normal loudness perception in the whole dynamic range of acoustic input. For each electrode, the lower and upper limit of electric stimulus have been defined by the values corresponding to “just audible” and just below “too loud”. Within this dynamic range, the stimulus strengths associated to the remaining verbal categories “very soft”, “soft”, “soft", “medium”, “loud” and “very loud” have been determined. The same loudeness categories were used for the scaling of acoustic stimuli. From both scaling experiments, the overall transduction of the CI system can be assessed and the parameters of a mapping function corresponding to a normal loudness growth can be calculated.

Results: The loudness growth functions of the electric stimuli exhibit a large variability even within the different channels of one subject. Nevertheless, the acoustic loudness growth functions obtained with the corresponding maps are roughly in accordance with the range covered by normal hearing subjects.

Conclusions: Deviations from optimum mapping can be corrected at least partially by manipulation of the parameters of the mapping function. This is facilitated by the function describing the overall transduction from acoustic sound pressure level to electric stimulus strength. In many cases, however, one mapping function is not sufficient for all channels. Therefore, the results are in favour of the development of channel-specific mapping function parameters in future CI systems.