Speech Recognition as a Function of the Number of Electrodes Used in the SPEAK Cochlear Implant Speech Processor Speech recognition was measured in listeners with the Nucleus-22 SPEAK speech processing strategy as a function of the number of electrodes. Speech stimuli were analyzed into 20 frequency bands and processed according to the usual SPEAK processing strategy. In the normal clinical processor each electrode is assigned to represent the ... Research Article
EDITOR'S AWARD
Research Article  |   October 01, 1997
Speech Recognition as a Function of the Number of Electrodes Used in the SPEAK Cochlear Implant Speech Processor
 
Author Affiliations & Notes
  • Kim E. Fishman
    House Ear Institute Los Angeles, CA
  • Robert V. Shannon
    House Ear Institute Los Angeles, CA
  • William H. Slattery
    House Ear Institute Los Angeles, CA
Article Information
Hearing & Speech Perception / Hearing Aids, Cochlear Implants & Assistive Technology / Speech, Voice & Prosody / Hearing / Research Articles
Research Article   |   October 01, 1997
Speech Recognition as a Function of the Number of Electrodes Used in the SPEAK Cochlear Implant Speech Processor
Journal of Speech, Language, and Hearing Research, October 1997, Vol. 40, 1201-1215. doi:10.1044/jslhr.4005.1201
History: Received November 20, 1996 , Accepted April 14, 1997
 
Journal of Speech, Language, and Hearing Research, October 1997, Vol. 40, 1201-1215. doi:10.1044/jslhr.4005.1201
History: Received November 20, 1996; Accepted April 14, 1997

Speech recognition was measured in listeners with the Nucleus-22 SPEAK speech processing strategy as a function of the number of electrodes. Speech stimuli were analyzed into 20 frequency bands and processed according to the usual SPEAK processing strategy. In the normal clinical processor each electrode is assigned to represent the output of one filter. To create reduced-electrode processors the output of several adjacent filters were directed to a single electrode, resulting in processors with 1, 2, 4, 7, 10, and 20 electrodes. The overall spectral bandwidth was preserved, but the number of active electrodes was progressively reduced. After a 2-day period of adjustment to each processor, speech recognition performance was measured on medial consonants, vowels, monosyllabic words, and sentences. Performance with a single electrode processor was poor in all listeners, and average performance increased dramatically on all test materials as the number of electrodes was increased from 1 to 4. No differences in average performance were observed on any test in the 7-, 10-, and 20-electrode conditions. On sentence and consonant tests there was no difference between average performance with the 4-electrode and 20-electrode processors. This pattern of results suggests that cochlear implant listeners are not able to make full use of the spectral information on all 20 electrodes. Further research is necessary to understand the reasons for this limitation and to understand how to increase the amount of spectral information in speech received by implanted listeners.

Acknowledgments
We thank the implant listeners who participated in this experiment for their patience and persistence—especially in the single-channel condition, which was an ordeal for them all. We appreciate the help of Steve Otto on speech processor fitting issues and editorial assistance; Mark Robert for help in plotting electrodograms; Fan-Gang Zeng, Sig Soli, and Michael Nilsson for help on statistical analysis; and the physicians and audiologists of the House Ear Clinic for their help in listener selection and recruitment. We appreciate the help of Norbert Dillier and his colleagues for providing the software to plot electrodograms. This study was partially funded by NIDCD grant R01-DC-01526.
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