Optimizing the number of electrodes with high-rate stimulation of the clarion CII cochlear implant

Objective-This blind crossover study evaluates the effect of the number of electrodes of the Clarion CII cochlear implant on speech perception in silence and in noise using a "high-rate" continuous interleaved sampling (CIS) strategy. Material and Methods-Nine users of this implant with 3-11 months of experience of an 8-channel CIS strategy [833 pulses per second (pps)/channel, 75 mus/phase] were fitted in a random order with 8-, 12- and 16-channel CIS strategies (+/-1400 pps/channel, 21 mus/phase). After I month of exclusive use of each strategy the performance was tested with consonant-vowel-consonant words in silence (sound only) and in speech-shaped background noise with signal-to-noise ratios (SNRs) of + 10, + 5, 0 and - 5 dB. Results-With "high-rate" strategies most patients' speech understanding in noise improved, although the optimum number of electrodes was highly variable. Generally, faster performers benefited from more active electrodes, whilst slower performers deteriorated. If each patient's optimal strategy was determined by a weighted sum of the test results at + 10, + 5 and 0 dB SNR, the average phoneme score improved from 57% to 72% at a SNR of + 5 dB, and from 46% to 56% at a SNR of 0 dB. The average phoneme score in silence was approximate to 85% for all strategies. Conclusion-We conclude that speech perception (especially in noise) can improve significantly with "high-rate" speech processing strategies, provided that the optimum number of electrodes is determined for each patient individually.