Improving consonant intelligibility for Ineraid patients fit with continuous interleaved sampling (CIS) processors by enhancing contrast among channel outputs

Objective: In Experiment 1 the objective was to determine whether patients who have been implanted with the Ineraid electrode array perform better on tests of consonant identification when signals are processed through a continuous interleaved sampling (CIS) processor than when signals are processed through an analogue (Ineraid) processor. In Experiment 2 the objective was to determine, for patients using the CIS strategy, whether identification accuracy for stop consonant place of articulation could be improved by enhancing differences in the patterns of the signal processor channel outputs. Design: In Experiment 1, 16 consonants were presented in VCV format for identification. In Experiment 1 the CIS patients evidenced difficulty in identifying /p t k/. Therefore, in Experiment 2 the voiceless stop consonants were presented in two stimulus conditions. In one, the stimuli were unfiltered. In the other, the stimuli were individually filtered so as to enhance the differences in channel outputs for /p/, /t/, and /k/. Results: In Experiment 1 the patients performed better with CIS processors than with analogue processors. In Experiment 2 the 'enhanced' stimuli were identified with better accuracy than were the unfiltered stimuli. Conclusions: We confirm that Ineraid patients achieve higher scores on tests of consonant identification when using a CIS processor than when using an analogue processor. Errors in identification of stop consonant place of articulation, when using a CIS processor, are due to the similarity in the patterns of the processor's channel outputs. By showing that consonant intelligibility can be improved by filtering, we show that we have not reached the limit of speech understanding that can be supported by the population of neural elements remaining in our patients' auditory systems.