Effects of Improper Spectral Delay on Speech Recognition with Cochlear Implants: A Simulation Study

Actual pulse rate in common cochlear implant systems is an essential parameter in terms of recognition performance and preference of patients. Finding the ideal pulse rate seems to be an evergreen topic independently of the used encoding strategy and architecture of the electrode array. At the same time, implantees react sensitively to rate changes, which makes the design of such trials difficult. We give a simplified model of spectral delays caused by a given total pulse rate, and compare these delays to natural cochlear delays. The comparison is carried out by feeding a hidden Markov model based speech recognizer with an adequately preprocessed speech corpus. Simulation outcomes give an insight why both too low and too high total pulse rates manifest in poor performance, and give a prediction on the recognition capabilities of each phone at various pulse rates. The experiments included in this study emphasize the importance of biotic cochlear delays and urge their application in future cochlear implant speech processing strategies.