title: Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants.
abstract: Current steering in partial tripolar (pTP) mode has been shown to improve pitch perception and spectral resolution with cochlear implants (CIs). In this mode, a fraction (σ) of the main electrode current is returned within the cochlea and steered between the basal and apical flanking electrodes (with a proportion of α and 1 - α, respectively). Pitch generally decreases when α increases from 0 to 1, although the salience of pitch change varies across CI users. This study aimed to identify the mechanism of pitch changes with pTP-mode current steering and the factors contributing to the intersubject variability in pitch-ranking sensitivity. The electrical fields were measured for steered pTP stimuli on the same main electrode with α = 0, 0.5, and 1 in five implanted ears using electrical field imaging (EFI). The related excitation patterns were also measured physiologically using evoked compound action potential (ECAP) and psychophysically using psychophysical forward masking (PFM). Consistent with the pitch-ranking results in this study, the EFI, ECAP, and PFM centroids shifted apically with increasing α. An apical shift was also observed for the PFM peak but not for the EFI or ECAP peak. The pattern width was similar with different α values within a given measure (e.g., EFI, ECAP, or PFM), but the ECAP patterns were broader than the EFI and PFM patterns, possibly because ECAP was measured with smaller σ values than EFI and PFM. The amount of pattern shift with α depended on σ (i.e., the total amount of current used for steering) but was not correlated with the pitch-ranking sensitivity across subjects. The results revealed that the pitch changes elicited by pTP-mode current steering were not only driven by the shifts of excitation centroid.
authors.affiliation: Department of Speech, Language, and Hearing Sciences, Purdue University, 715 Clinic Drive, West Lafayette, IN, 47907, USA.|School of Electrical and Computer Engineering, Purdue University, 715 Clinic Drive, West Lafayette, IN, 47907, USA.
authors.forename: Ching-Chih
authors.initials: CC
authors.lastname: Wu
authors.affiliation: Department of Speech, Language, and Hearing Sciences, Purdue University, 715 Clinic Drive, 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.forename: Xin
authors.initials: X
authors.lastname: Luo
mesh_terms: D000200:Action Potentials; D000368:Aged; D000369:Aged, 80 and over; D003051:Cochlea / Q000502:physiology*; D003054:Cochlear Implants; D004558:Electric Stimulation; D006801:Humans; D008875:Middle Aged; D010470:Perceptual Masking; D010898:Pitch Perception
keywords: cochlear implant; compound action potential; current focusing; current steering; electrical field imaging; forward masking pattern; spread of excitation; tripolar mode