Cochlear implant channels with high thresholds degrade medial vowel perception

There is considerable evidence that the functional interface between cochlear implant electrodes and the auditory nerve varies from channel to channel within individual patients. Recently a method was proposed to gauge the status of a channel’s interface on the basis of its threshold to focused stimulation using tripolar electrode configuration. This approach showed that channels with high tripolar thresholds have broader psychophysical tuning curves. In this study, the relationship between the number and distribution of high threshold channels with medial vowel identification in a bvt paradigm was examined. Tripolar thresholds were measured for all channels in seven listeners. Vowel identification was tested in the sound field with six repetitions. On the basis of each listener’s electrodogram (the sound processor output of current amplitude as a function of time and channel), the similarity of the vowels using a principle component analysis was examined. We then related the vowel confusions based on the electrodogram of different subsets of channels, based on basal to apical location or tripolar threshold. Preliminary results suggest that the channels with high tripolar thresholds, or in regions of high variability in tripolar threshold, can account for a significant amount of the variance in subject performance. [Work supported by NIH Grant No. DC8883.]