Vowel confusion patterns in children and adults with cochlear implants

Abstract

Suboptimal interfaces between cochlear implant (CI) electrodes and their target neurons may distort the spectral information that is important for vowel identification. The goal of this investigation was to relate vowel confusion patterns of CI users to their site-specific (i.e., frequency-specific) variation in electrode-neuron interface across the electrode array. The electrode-neuron interface is estimated using single-channel detection thresholds with a spatially focused electrode configuration; elevated thresholds indicate channels with relatively poorer frequency transmission. We hypothesized that higher focused thresholds on channels transmitting low frequency (<983 Hz) information would be associated with errors in vowel height, whereas higher thresholds on channels transmitting mid- and high-frequency (>984 Hz) information would be related to vowel advancement errors. Vowel recognition was assessed with a closed set of medial vowels in 4-talker babble noise. Focused thresholds were measured on electrodes 2–15. Vowel confusions were examined according to the direction of errors in 2-dimensional physical articulatory and acoustic F1-F2 space. Results showed that higher average focused thresholds on the 3 most basal electrodes tested (2327–4630 Hz) were associated with perception of front vowels as more back. These findings suggest that suboptimal electrode-neuron interfaces could systematically affect CI listeners’ perception of vowel characteristics.