Current steering and electrode spanning with partial tripolar stimulation mode in cochlear implants

Cochlear implants (CIs) partially restore hearing sensation to profoundly deaf people by electrically stimulating the surviving auditory neurons. However, CI users perform poorly in challenging listening tasks such as speech recognition in noise and Cochlear implants (CIs) partially restore hearing sensation to profoundly deaf people by electrically stimulating the surviving auditory neurons. However, CI users perform poorly in challenging listening tasks such as speech recognition in noise and music perception, possibly due to the small number of implanted electrodes and the large current spread of electric stimulation. Although current spread may be reduced using partial tripolar (pTP) stimulation mode, the number of electrodes may not be sufficient to preserve fine spectral details. Here, we propose to introduce current steering and electrode spanning to pTP mode to create additional spectral channels for CI users. Loudness and pitch perception with steered and spanned pTP modes were simulated using a computational model of CI stimulation and were tested in CI users. The excitation pattern of each stimulation mode was also measured at the physical (i.e., intra-cochlear electrical potential distribution), neural (i.e., spatial profile of evoked compound action potential), and perceptual levels (i.e., psychophysical forward masking pattern). Consistent with the model predictions, pitch-ranking results verified the feasibility and efficacy of the proposed stimulation modes in eliciting distinctive pitches for CI users. Pitch increased when the centroid of excitation pattern was shifted basally. When the centroid of excitation pattern did not move, higher pitches were perceived for narrower excitation patterns. These results suggest that in pTP-mode CI processing strategies, current steering and electrode spanning may provide additional spectral channels for better coding of spectral fine structures and for handling the cochlear dead region and defective electrode contact