A temporal limits encoder for cochlear implants

Abstract

Cochlear implant (CI) strategies extract multi-channel temporal envelopes to stimulate an array of electrodes. However, temporal pitch perception ability is known to be limited to a low frequency range at single channels. Therefore, this study proposes a temporal limits encoder (TLE) to make full use of the temporal processing abilities at each individual channels. First the total bandwidth is allocated to uniform narrow-bands, which are then down-shifted to the CI user's low frequency range (about 50–250 Hz) of temporal pitch. After the slowly varying signals are processed by half-wave rectification, the rectified signals are compressed and used to amplitude modulate interleaved high constant rate pulse sequences. By first deriving slowly varying signals, more information or even novel information about the original signal can be preserved based on the perceptual abilities of the implantees. Preliminary psychoacoustic frequency discrimination experiments suggest that the proposed TLE strategy can offer finer frequency resolution abilities.