Conditions for generating virtual channels in cochlear prosthesis systems

Simultaneous electrical stimulation of neighboring electrodes in cochlear prosthesis systems generates channel interaction. However, intermediate channels, or virtual channels between the neighboring electrodes can be created through controlled channel interaction. This effect may be exploited for sending new information to the hearing nerves by stimulating in a suitable manner. The actual stimulation sites are therefore not limited to the number of electrodes. Clinical experiments, however, show that virtual channels are not always perceived. In this paper, electrical simulation with finite element analysis on a half turn human cochlea model is adopted to model the virtual channel effect, and the conditions for generating virtual channels are discussed. Five input current ratios (100/0, 70/30, 50/50, 30/70, 0/100) are applied to generate virtual channels. Three electrode arrays parameters are taken into consideration: distance between electrode contact and modiolus, spacing between adjacent electrode contacts and scale of electrode contact size. By observing the activating function contours, the virtual channel patterns and performances can be measured and examined. The results showed that a broad excitation pattern is necessary to produce the kind of electrode interaction that can form distinct virtual channels.