Polyphonic pitch perception in cochlear implant users

Abstract

Cochlear implant (CI) devices take advantage of the tonotopic organization of the auditory nerve to provide moderate speech recognition. While commercial place-pitch strategies are sufficient for speech comprehension in quiet conditions, CI users struggle to detect multiple, simultaneous sources of pitch. In a polyphonic pitch-trajectory task, two streams (low and high pitch) are presented simultaneously. Participants perform a 1-interval-4-alternative forced-choice procedure to identify which stream changed in pitch and whether it went higher or lower in pitch (low-lower/low-higher/high-lower/high-higher). The low and high streams are high-rate pulsetrains modulated at 110 Hz and 220 Hz, respectively. The stimulus is 1 s in duration and the target stream contains an ascending or descending modulation-frequency sweep over the last 200 ms. The low stream will be presented to the most apical electrode and the high stream presented to electrode separations of 0, 2, 4, and 8. Preliminary results indicate that CI users perform better on the electrode psychophysical tasks than on acoustic variations. Additionally, performance is improved with sharper temporal envelopes. These results suggest that CI users are able to perceive polyphonic pitch and that resolution is limited by how temporal information is conveyed by clinical devices.