Electrode interactions in cochlear implants

1
Electrode interactions in cochlear implants
Poster 32

• Qing Tang and Fan-Gang Zeng

Hearing and Speech Research Laboratory,
Department of Otolaryngology, University of
California, Irvine

• 3. Monopolar configuration (Loudness summation
  with simultaneous stimulation).

• 2. Bipolar configuration (Threshold 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.

• 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).

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 Am 114(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 Am 49 467.
• Middlebrooks, J. C. (2004) Effects of
  cochlear-implant pulse rate and inter-channel
  timing on channel interactions and thresholds" J
  Acoust Soc Am 116(1) 452-468.
• van den Honert, C. et al. (1984). Single fiber
  mapping of spatial excitation patterns in the
  electrically stimulated auditory nerve." Hearing
  Res 29 195-206.
• White, M. W. et al. Multichannel cochlear
  implants Channel interactions and processor
  design." Archives of Otolaryngology 110 493-501.
• Wilson, B. S. et al. Better speech recognition
  with cochlear implants." Nature 352 236-238.

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.