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Electrode interactions in cochlear implants

Poster 32. Hearing and Speech Research Laboratory, Department of Otolaryngology, University of California, Irvine. 3. Monopolar configuration (Loudness summation with simultaneous stimulation).

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Electrode interactions in cochlear implants

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  1. Poster 32 Hearing and Speech Research Laboratory, Department of Otolaryngology, University of California, Irvine 3. Monopolar configuration (Loudness summation with simultaneous stimulation). 1). Increased loudness could be due to electrical field addition in the case of total electrode interaction or loudness summation in the case of no electrode interaction. 2). Stimulation rate did affect electrode interaction, although this difference was due to either more electrode interaction or different loudness growth function at high rate stimulation. 2. Bipolar configuration (Threshold summation with simultaneous stimulation). Electrode interactions in cochlear implants • Electrode interaction greatly limits cochlear implant performance. The present study systematically evaluated electrode interaction in Clarion II subjects, Both threshold summation and loudness summation were studies as a function of the following 4 parameters: • monopolar vs. bipolar configurations • stimulation rate • electrode separation • simultaneous vs. interleaved stimulation 1. Monopolar configuration (Threshold summation with simultaneous stimulation). 1). Bipolar stimulation showed less but more complex electrode interaction patterns compared to monopolar stimulation. Subject CI 1 showed no electrode interaction at all electrode separations. Subject CI 2 showed electrode interaction only at the smallest electrode separation. Subject CI 5 showed total electrode interaction at all electrode separations with no phase influence. 2). Stimulation rate did not affect electrode interaction. 1). Monopolar stimulation produced total electrode interaction between electrode pair (1,0) and (3,0) as well as (1,0) and (9,0), but no electrode interaction between electrode pair (1,0) and (15,0). 2). Electrode interaction in simultaneous stimulation is determined by linear electrical field addition. 3). Stimulation rate did not affect electrode interaction. CI 5 CI 1 CI 1 CI 3 1000Hz 100 Hz 5154 Hz 5154Hz METHODS • Threshold summation was measured by a three-alternative, forced-choice (3AFC), adaptive procedure with a two-down, one-up rule. • Loudness summation was measured by a loudness balance (“bracket”) procedure between single-electrode and dual-electrode stimulation at the comfortable level. 4. Monopolar configuration (Threshold summation with interleaved stimulation,100 Hz). Qing Tang and Fan-Gang Zeng 1). Interleaved stimulation produced less electrode interaction than simultaneous stimulation. 2). Electrode interaction with interleaved stimulation decreased with increasing time interval between masker and probe electrodes, and disappeared if the time interval is larger than 1293.6 us. 3). Whether the masker and the probe were in phase or out of phase, they produced the same effects. In 3 out of 4 subjects, the electrode interaction between masker and probe reduced the threshold for the probe. CI 2 CI 5 CI 6 CI 3 CI 2 1000 Hz 5154 Hz • REFERENCES • Boex, C. et al. (2003). “Electrical field interactions in different cochlear implant systems." J Acoust Soc Am114(4): 2049-57. • Kral, A. et al. (1998). “Spatial resolution of cochlear implans: the electrical field and excitation of auditory afferents." Hear. Res.121: 11-28. • Levitt, H. (1971). “Transformed up-down methods in psychoacoustics." J Acoust Soc Am49: 467. • Middlebrooks, J. C. (2004) “Effects of cochlear-implant pulse rate and inter-channel timing on channel interactions and thresholds" J Acoust Soc Am116(1): 452-468. • van den Honert, C. et al. (1984). “Single fiber mapping of spatial excitation patterns in the electrically stimulated auditory nerve." Hearing Res29: 195-206. • White, M. W. et al. “Multichannel cochlear implants: Channel interactions and processor design." Archives of Otolaryngology110: 493-501. • Wilson, B. S. et al. “Better speech recognition with cochlear implants." Nature352: 236-238. 100 Hz 5154 Hz CI 4 CI 5 MAJOR FINDINGS 1). Electrode interaction is spatial and timing dependent. 2). With simultaneous stimulation, electrode interaction is mainly determined by electrical field addition and loudness summation. 3). With interleaved stimulation, electrode interaction is mainly determined by neural interaction and loudness summation. 4). Bipolar stimulation produced narrower excitation than monopolar stimulation. ACKNOWLEDGEMENTS We would like to thank Leonid Litvak and Tiffany Elise H. Chua for their help. We would also like to thank our CI subjects for their time and dedication. This experiment was supported by NIH Grant 2R01 DC002267.

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