Effects of stimulation rate on modulation detection and speech recognition by cochlear implant users

Objective: This study investigated the effect of low to moderate electrical stimulation rates (275, 350, 500 and 900 pps/ch) on modulation detection ability of cochlear implant subjects, and the relationship between modulation detection and speech perception as a function of rate. Design: A repeated ABCD experimental design for the four rate conditions was employed. A sinusoidally amplitude modulated acoustic signal was presented to the audio input of a research processor. Stimuli were presented at an acoustic level that produced electrical levels close to the subjects' most comfortable level (MCL) of stimulation and at an acoustic level 20 dB below this. Study Sample: Ten postlingually deaf adult users of the Nucleus CI24 cochlear implant participated. Results: Acoustic modulation detection thresholds (MDTs), averaged across the subject group, were significantly better for rates of 500 pps/ch compared to the other rates examined for stimuli presented at MCL. In addition, there was a significant relation between speech perception in noise and acoustic MDTs at MCL. Conclusions: The benefits obtained in speech perception and modulation detection as a function of rate were attributed to an increased electrical dynamic range as a function of stimulation rate, at least for rates up to 500 pps/ch.