title: Symmetric Electrode Spanning Narrows the Excitation Patterns of Partial Tripolar Stimuli in Cochlear Implants.
abstract: In cochlear implants (CIs), standard partial tripolar (pTP) mode reduces current spread by returning a fraction of the current to two adjacent flanking electrodes within the cochlea. Symmetric electrode spanning (i.e., separating both the apical and basal return electrodes from the main electrode by one electrode) has been shown to increase the pitch of pTP stimuli, when the ratio of intracochlear return current was fixed. To explain the pitch increase caused by symmetric spanning in pTP mode, this study measured the electrical potentials of both standard and symmetrically spanned pTP stimuli on a main electrode EL8 in five CI ears using electrical field imaging (EFI). In addition, the spatial profiles of evoked compound action potentials (ECAP) and the psychophysical forward masking (PFM) patterns were also measured for both stimuli. The EFI, ECAP, and PFM patterns of a given stimulus differed in shape details, reflecting the different levels of auditory processing and different ratios of intracochlear return current across the measurement methods. Compared to the standard pTP stimuli, the symmetrically spanned pTP stimuli significantly reduced the areas under the curves of the normalized EFI and PFM patterns, without shifting the pattern peaks and centroids (both around EL8). The more focused excitation patterns with symmetric spanning may have caused the previously reported pitch increase, due to an interaction between pitch and timbre perception. Being able to reduce the spread of excitation, pTP mode symmetric spanning is a promising stimulation strategy that may further increase spectral resolution and frequency selectivity with CIs.
authors: Department of Speech, Language, and Hearing Sciences, Purdue University, 715 Clinic Dr., West Lafayette, IN, 47907, USA. xinluo@asu.edu.|Department of Speech and Hearing Science, Arizona State University, Coor Hall, 975 S. Myrtle Av., P.O. Box 870102, Tempe, AZ, 85287, USA. xinluo@asu.edu.
authors: Xin
authors: http://orcid.org/0000-0002-7400-5520
authors: X
authors: Luo
authors: Department of Speech, Language, and Hearing Sciences, Purdue University, 715 Clinic Dr., West Lafayette, IN, 47907, USA.|School of Electrical and Computer Engineering, Purdue University, 465 Northwestern Av., West Lafayette, IN, 47907, USA.
authors: Ching-Chih
authors: CC
authors: Wu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003054:Cochlear Implants; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D008875:Middle Aged; D010898:Pitch Perception; D011571:Psychoacoustics
keywords: cochlear implant; current focusing; electrical field imaging; electrode spanning; evoked compound action potential; forward masking pattern; spread of excitation; tripolar mode