gms | German Medical Science

Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants

Medical University of Hannover

01.06. bis 04.06.2005, Hannover

Correlation of NRT™ recovery function parameters and speech perception results for different stimulation rates

Meeting Abstract

  • corresponding author R.D. Battmer - Department of Otolaryngology, Medical University of Hannover, Germany
  • W.K. Lai - Department of Otorhinolaryngology, University Hospital, Zürich, Switzerland
  • N. Dillier - Department of Otorhinolaryngology, University Hospital, Zürich, Switzerland
  • J. Pesch - Cochlear Staff, Mechelen and Hannover
  • M.J. Killian - Cochlear Staff, Mechelen and Hannover
  • T. Lenarz - Department of Otolaryngology, Medical University of Hannover, Germany

Medical University of Hannover, Department of Otolaryngology. Fourth International Symposium and Workshops: Objective Measures in Cochlear Implants. Hannover, 01.-04.06.2005. Düsseldorf, Köln: German Medical Science; 2005. Doc05omci014

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Veröffentlicht: 31. Mai 2005

© 2005 Battmer et al.
Dieser Artikel ist ein Open Access-Artikel und steht unter den Creative Commons Lizenzbedingungen (http://creativecommons.org/licenses/by-nc-nd/3.0/deed.de). Er darf vervielf&aauml;ltigt, verbreitet und &oauml;ffentlich zug&aauml;nglich gemacht werden, vorausgesetzt dass Autor und Quelle genannt werden.


Gliederung

Text

Cochlear recently released the Nucleus Freedom™ System with the Nucleus Freedom Cochlear Implant (CI24RE). The CI24RE contains an improved NRT™ amplifier with a low noise floor of 1μV rms. This new amplifier allows for faster and more accurate NRT recordings. Furthermore the Freedom Cochlear Implant offers a wider range of speech coding strategies using stimulation rates of up to 32.000 pulses per second. In order to make use of these possibilities it would be helpful to find a predictor of the optimal settings for a given subject, especially regarding the stimulation rate. In an earlier study (Shpak et al. 2004) a correlation between the preferred stimulation rate and a single parameter derived from NRT measurements of the nerves refractory behaviour has been shown. In our investigation the enhanced NRT capabilities of the new implant were used to gain deeper insight into the NRT recovery function and it's relation to speech perception results with different stimulation rates. The recovery functions were measured with varying Masker Probe Intervals (MPI) making use of the Masked Response Extraction (MRE) method. In each recipient recovery functions were measured on different electrodes using different masker and probe current levels (CL). Recovery functions were fitted with an exponential model which is defined by three parameters reflecting the maximal amplitude of the neural response at saturation level (A), the absolute refractory period (T0) and the time constant of recovery during the relative refractory period (α). The recovery functions recorded on different electrodes and at different stimulation levels were compared by means of their T0 and α. For those recipients who have completed a sequence of speech perception tests with different stimulation rates (500, 1200, 3500 Hz) the parameters (T0 , α) were analyzed with regard of the rate of best speech perception results. The results show that the time constants T0 and α vary with different CLs: with increasing CLs T0 decreases and a increases. Preliminary comparisons between T0, α and the speech perception results with different stimulation rates demonstrated no correlation. However, further characteristics of the recovery function especially at very short MPI will be investigated and might show a better relationship to rate preference.