Consonant and vowel confusions in well-performing adult cochlear implant users, measured with a nonsense syllable repetition test

ObjectiveThe study's objective was to identify consonant and vowel confusions in cochlear implant (CI) users, using a nonsense syllable repetition test.DesignIn this cross-sectional study, participants repeated recorded mono- and bisyllabic nonsense words and real-word monosyllables in an open-set design.Study sampleTwenty-eight Norwegian-speaking, well-performing adult CI users (13 unilateral and 15 bilateral), using implants from Cochlear, Med-El and Advanced Bionics, and a reference group of 20 listeners with normal hearing participated.ResultsFor the CI users, consonants were confused more often than vowels (58% versus 71% correct). Voiced consonants were confused more often than unvoiced (54% versus 64% correct). Voiced stops were often repeated as unvoiced, whereas unvoiced stops were never repeated as voiced. The nasals were repeated correctly in one third of the cases and confused with other nasals in one third of the cases. The real-word monosyllable score was significantly higher than the nonsense syllable score (76% versus 63% correct).ConclusionsThe study revealed a general devoicing bias for the stops and a high confusion rate of nasals with other nasals, which suggests that the low-frequency coding in CIs is insufficient. Furthermore, the nonsense syllable test exposed more perception errors than the real word test.