Investigating the influence of pulse rate and duration on pitch perception in cochlear implants
Multi-rate sound processing strategies may potentially provide improved speech recognition and music perception in cochlear implants, although it may be necessary to tune these strategies using psychophysical data to provide maximum benefit to the user. To investigate the need for tuning, cochlear implant users participated in several rate-based psychophysical experiments. Subjects performed single-and two-rate pitch ranking tasks to investigate the influence of pulse rate on the overall pitch structure. The introduction of a second rate resulted in frequent pitch reversals between closely spaced electrodes. In addition to the multi-rate pitch structure, the duration necessary to perceive a rate change must also be considered. Experiments were performed using ABA stimuli, where rate B was higher than rate A. Subjects completed an embedded rate discrimination task in which the duration of B was fixed and its rate varied adaptively for durations ranging from 20-200 ms. The rate of segment B was then fixed, and its duration varied adaptively. Results imply that embedded rate difference limens may not be a function of duration, and that the minimum duration required for detecting a change in pulse rate is subject specific.
