The effect of stimulation rate on speech perception in individuals using Nucleus Freedom Cochlear Implant

The aim of the present study was to investigate the effect of high electrical stimulation rates in cochlear implants (CI) on speech perception. Four participants using Nucleus Freedom CI and five adult participants with normal hearing performed a vowel consonant vowel (VCV) consonant (iCi) recognition task in quiet and a (Bamford-Kowal-Bench) BKB sentence recognition task in noise at +10 dB signal to noise ratio (SNR). The performance of the participants was measured for three stimulation rates, namely 1800 pulses per second per channel (pps/ch), 2400 pps/ch and 3500 pps/ch, with the Advanced Combination Encoder Revised i.e. ACE (RE) speech coding strategy. Participants with normal hearing were also studied to see the effect of overlap on CI acoustic modelling. The speech perception results of the participants using the Nucleus Freedom system were compared with those of participants with normal hearing on CI acoustic modelling. The VCV test scores were further analyzed for feature transmission errors in place and manner of articulation as well as in voicing features. The results showed that there was no advantage of high stimulation rates for both consonant recognition in quiet and sentence recognition in noise. The CI acoustic models were found to be useful in studying the effect of rates in those using a CI. Although CI acoustic model with overlap lead to poor performance in consonant recognition in quiet and sentence recognition in noise test, they seemed to be the better approximation of the scores among the users of CI