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Speech understanding and preference of cochlear implant recipients using FSP speech coding strategy
(MedEl) after conversion to FS4-LR and FS4-HR
Klünter H.D. , Pyschny V. , Fürstenberg D. , Klävers J. , Walger M. , Lang-Roth R.
University of Cologne, Department of Otorhinolaryngology, Head and Neck Surgery, Cologne, Germany
Speech coding strategies commonly transmit additional signal envelope information to enhance speech
perception but nevertheless, the processing of temporal fine structure remains poor. Therefore zero crossings of
the sound signal are identified and computed in addition to the envelope by the Fine Structure Processing
strategies FSP and FS4 (MedEl, Austria). The information can be transmitted at a varied number of 1 to 3 apical
electrodes with channel specific sampling sequences (CSSS) in the FSP-strategy or fixed in four electrodes in
the FS4-strategy. Because the stimulation of the fine structure beyond 1 kHz takes more time, higher stimulationlevels with increased pulse-width result in a decrease of CSSS-channels in the standard FSP strategy. As the
number of CSSS-channels in FS4 is fixed at low stimulation rate (FS4-LR) the stimulation may result in a loss of
information in higher frequencies. In additional development of the FS4 coding strategy, MedEl increased the
stimulation rate (FS4-HR) to compensate information loss.
In a prospective double blind study with classic crossover design, postlingually deafened adult CI users (n=14)
were randomly provided with speech coding strategy FSP and converted for the period of 6 weeks to the
encoding strategy FS4-LR. After a period of at least 6 months, the same population (n=9) with the same
experimental protocol received FS4-HR. The evaluation of speech intelligibility was performed with standardized
speech tests in silence and noise (Freiburger, Oldenburger (OLSA) and Göttinger (GOESA) speech tests). In a
simple preference test at the end of the study, the subjects were asked to decide with which coding strategy
speech understanding is better. Statistics were performed with SPSS (Wilcoxon, p < 0.05).
In Freiburger, GOESA and OLSA in silence, the subjects achieved significantly worse results after conversion to
FS4. Thus, the understanding of Freiburger-monosyllables at 65 dB SPL in quiet decreased from 55.42% to
41.67%, in the OLSA from 89.83% to 84% and from 75.70% to 60.02% in GOESA. In noise the decrease was
smaller, but comparable in tendency. For the FS4-HR coding strategy, the results are still pending. While the
majority of subjects in the preference test decided against FS4-LR in the first cycle, FS4-HR were evaluated in
the second section as equally well with the default Strategy (FSP).
The hypothesis that an increased and fixed number of fine-structure channels, as well as the higher temporal
resolution and the related accurate transmission of the sound characteristics at lower frequencies could result in
improved speech understanding, could not be confirmed on the basis of our data for the FS4-LR coding strategy.
To what extent the modified FS4 speech coding strategy (FS4-HR) provides a better speech understanding, the
analysis of the second part study data will demonstrate. The subjective acceptance of FS4 HR compared to FS4LR is obviously higher.