Investigation of pitch discrimination and the effect of learning for virtual channels realized by current steering

As virtual channels could be perceived by the majority of implant users, they promise potential for advanced speech coding strategies, providing enhanced spectral resolution. An improvement in resolution was found from first stimulation up to 6 months afterwards.

Independent current sources allow distribution of the current between adjacent electrode contacts in a defined ratio, thus steering the current. The goal of our study was to investigate a) whether all users were able to distinguish between adjacent physical channels, b) how many users could perceive a distinct pitch as the current was steered between two adjacent contacts and c) whether a learning effect was observed.

A pitch ranking measurement was performed during an acute test session for a group of 39 cochlear implant users. The results were analysed with respect to the implanted electrode system. The learning process during the first 6 months after implantation was investigated for a selected subgroup.

About half of the study participants were able to perceive intermediate channels; 5% were able to discriminate more than eight intermediate channels, which correspond to half of the physical channels. A wide variation was found across the array.