Effects of the Number of Channels and Channel Stimulation Rate on Speech Recognition and Sound Quality Using Precurved Electrode Arrays

This study investigated the relationship between the number of active electrodes, channel stimulation rate, and their interaction on speech recognition and sound quality measures while controlling for electrode placement. Cochlear implant (CI) recipients with precurved electrode arrays placed entirely within scala tympani and closer to the modiolus were hypothesized to be able to utilize more channels and possibly higher stimulation rates to achieve better speech recognition performance and sound quality ratings than recipients in previous studies. Participants included seven postlingually deafened adult CI recipients with Advanced Bionics Mid-Scala electrode arrays confirmed to be entirely within scala tympani using postoperative computerized tomography. Twelve conditions were tested using four, eight, 12, and 16 electrodes and channel stimulation rates of 600 pulse per second (pps), 1,200 pps, and each participant's maximum allowable rate (1,245-4,800 pps). Measures of speech recognition and sound quality were acutely assessed. For the effect of channels, results showed no significant improvements beyond eight channels for all measures. For the effect of channel stimulation rate, results showed no significant improvements with higher rates, suggesting that 600 pps was sufficient for maximum speech recognition performance and sound quality ratings. However, across all conditions, there was a significant relationship between mean electrode-to-modiolus distance and all measures, suggesting that a lower mean electrode-to-modiolus distance was correlated with higher speech recognition scores and sound quality ratings. These findings suggest that even well-placed precurved electrode array recipients may not be able to take advantage of more than eight channels or higher channel stimulation rates (> 600 pps), but that closer electrode array placement to the modiolus correlates with better outcomes for these recipients.