Download 13th International Conference on Cochlear Implants and Other

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Transcript
S21-16
A new stimulation mode: the virtual tripole
1,2
Padilla M. , Landsberger D.M.
1,2
1
New York University School of Medicine, Otolaryngology, New York, United States, 2House Ear Institute, Communication Auditory
Neuroscience, Los Angeles, United States
Spectral resolution is a limiting factor in performance with cochlear implants. Current shaping techniques have
been used in attempts to improve spectral resolution. Current steering (e.g. virtual channels) has been used to
increase the number of channels beyond the number of electrodes. Current focusing (e.g. partial tripolar
stimulation) has been used to reduce the interaction across two channels in order to increase the independence
of each channel and therefore improve spectral resolution.
We propose a new stimulation mode called a virtual tripole (VTP), which is a modification of a traditional tripole.
The VTP is designed to reduce spread of excitation as well as allow for current steering. Tripolar stimulation
consists of stimulation on one electrode combined with simultaneous out-of-phase stimulation on adjacent
electrodes to reduce the spread of current. With a VTP, each of the three electrodes in a tripole is replaced with
a virtual channel, theoretically allowing for both current focusing and current steering.
Six users of the CII or HiRes90K Advanced Bionics device have participated in this study. Spread of excitation
was measured for monopolar, partial tripolar (σ = 0.75) and VTP (σ = 0.75 and 1) maskers located at electrode 9
using a forward masking technique. The probes were partial tripolar (σ = 0.75) pulse trains located at electrodes
6 through 12. Spread of excitation was also measured for monopolar virtual and VTP (σ = 0.75 and 1, when
possible) maskers located at electrode 8.5. The probes were VTP (σ = 0.75), located at electrodes 6.5 through
10.5. Results suggest that VTP stimulation provides a reduction in spread of excitation compared to the spread
from monopolar stimulation. VTP (σ = 1) stimulation provides a narrower spread of excitation than partial VTP (σ
= 0.75) stimulation. However, partial tripolar (σ = 0.75) stimulation using physical electrodes seems to produce a
narrower spread of excitation than even a full VTP (σ = 1) stimulus. Effect on spectral resolution was measured
using a modified spectral ripple task, the SMRT task (Aronoff and Landsberger, 2013). Subjects tested showed
better spectral resolution with a VTP compared to MP stimulation.
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