Pitch ranking using sung vowels in cochlear implants: a comparison of monopolar and tripolar stimulation

Cochlear implant listeners typically perform poorly in tasks of complex pitch perception. One explanation is that wide current spread during implant activation creates channel interactions that may interfere with delivery of across-channel temporal information. Current focusing using a tripolar mode of stimulation has been proposed as a way of reducing channel interactions, minimising spread of excitation and potentially improving place and temporal pitch cues. The present study evaluated the effect of mode on performance of CI listeners on a pitch ranking task using male and female sung vowels separated by either a half or a quarter octave. Results were variable across participants, but on average pitch ranking was at chance level when the pitches were a quarter octave apart, and improved when the difference was a half octave. No advantage was observed for tripolar over monopolar mode in pitch ranking of sung vowels at either interval, suggesting that previously published psychophysical advantages for focused modes may not translate into improvements in pitch perception. Evaluation of the centre of gravity of the stimulation pattern, plus a lack of significant difference between male and female voices, suggested that participants may not have been able to access temporal pitch cues in either mode.