Reduction of Electrical Interaction in Auditory Prostheses

The spread of current in multichannel implants results in excitation of largely identical neural populations regardless of which electrode is stimulated. This severely reduces the number of independent channels of information conveyed with monopolar or even bipolar stimulation. A method based on the thresholds of multiple electrode stimuli was developed to calculate accurately the mapping from electrode current levels to excitation levels at each neural site. For the implant subjects tested, this technique accurately predicted thresholds for arbitrary patterns of stimulation. Inverting this mapping matrix produced patterns, of stimulation that selectively stimulated only one neural site with a minimum of interaction, while satisfying current limit constraints. These sharpened stimuli exhibited lower interaction and were pitch ranked with greater consistency than either monopolar or bipolar stimuli.