Temporal and intensity processing in cochlear implants

The dissertation consists of two related yet independent psychophysical studies to improve cochlear implant (CI) performance. The first study focuses on discrimination of temporal patterns in cochlear implants. The temporal patterns covered a wide range of mean rates from temporal envelope (2--50 Hz), periodicity (50--500 Hz) and fine structure (>500 Hz). Psychophysical results from actual CI users of Nucleus devices showed a great deal of individual variability in discriminating temporal patterns, with the best users being able to differentiate fine temporal patterns. The second study focuses on intensity coding with different electrical stimulation waveforms (standard biphasic pulses and experimental delayed pseudo-monophasic pulses) and electrode configurations (monopolar and tripolar stimulation). Psychophysical results from CI users of Clarion devices showed that for both electrode configurations the experimental waveform lowers electric stimulation thresholds but maintains essentially the same maximal comfort level. The present results generally support the reintroduction of temporal fine structure cues to improve CI performance but predict limited benefits in either patient performance or power savings by manipulations of electric waveforms and electrode configurations.