Combining Place and Rate of Stimulation Improves Frequency Discrimination in Cochlear Implant Users

In the auditory system, frequency is represented as tonotopic and temporal response properties of the auditory nerve. While these response properties are inextricably linked in normal hearing, cochlear im-plants can separately excite tonotopic location and temporal synchrony using different electrodes and stimulation rates, respectively. This separation allows for the investigation of the contributions of tono-topic and temporal cues for frequency discrimination. The present study examines frequency discrimina-tion in adult cochlear implant users as conveyed by electrode position and stimulation rate, separately and combined. The working hypothesis is that frequency discrimination is better provided by place and rate cues combined compared to either cue alone. This hypothesis was tested in two experiments. In the first experiment, frequency discrimination needed for melodic contour identification was measured for frequencies near 10 0, 20 0, and 40 0 Hz using frequency allocation modeled after clinical processors. In the second experiment, frequency discrimination for pitch ranking was measured for frequencies between 10 0 and 1600Hz using an experimental frequency allocation designed to provide better access to place cues. The results of both experiments indicate that frequency discrimination is better with place and rate cues combined than with either cue alone. These results clarify how signal processing for cochlear implants could better encode frequency into place and rate of electrical stimulation. Further, the results provide insight into the contributions of place and rate cues for pitch.(c) 2022 Elsevier B.V. All rights reserved.