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FINE STRUCTURE PROCESSING IN COCHLEAR IMPLANTS

Peter Nopp1, Stefan Brill2, Clemens Zierhofer3, Peter Schleich1, Alexander Moeltner1, Ernst Aschbacher1

1MED-EL Medical Electronics GmbH, Innsbruck, Austria/2University ENT-Clinic Würzburg, Würzburg, Germany/3Christian Doppler Laboratory for Active Implantable Systems, Innsbruck, Austria

■ OBJECTIVES: The coding strategy provides the crucial algorithm in a cochlear implant, by mans of which the stimulation data are derived from the sound signal. Basically, all coding strategies which have been in use in cochlear implants for the last 15-20 years rely on the signal envelope and largely disregard the fine structure. Recently, research in normal hearing subject has shown that the fine structure of a sound signal is the main information carrier for music and tonal languages, whereas for speech it is the envelope. This could at least in part explain some of the performance deficits with cochlear implants.

■ METHODS: Based on these results and on results with combined electric and acoustic stimulation (EAS), MED-EL has developed a concept to present the fine structure of a sound in addition to the envelope via a cochlear implant. The first implementation of this concept is the FSP strategy in the OPUS speech processors.

■ RESULTS: Users of the FSP strategy show equal or improved speech perception and improved sound quality and music appreciation. Improved temporal coding can lead to improved frequency discrimination. Place coding is equally efficient with parallel and sequential stimulation. In addition, test results suggest that both the temporal code and the place code complement each other so that the user can make use of the code he is more sensitive to.

■ CONCLUSIONS: With fine structure coding it seems to be possible to at least in part mediate some of the performance deficits in cochlear implants.