Influence of Upper Frequency Boundary on Consonant Perception in Normal Hearing and Cochlear Implant Adults

Abstract

Purpose: Although some studies argue that it is worthy for cochlear implant (CI) users to have frequency information above 3,000 Hz for consonant recognition, it is not clear whether CI patients make use of this information, especially in Korean. In this experiment, we tested whether consonant recognition in CI patients depended on the utilization of information from 3,000 to 8,000 Hz. Methods: We conducted consonant recognition tests in Korean [3 syllable structures: vowel-consonant-vowel (VCV), consonant-vowel (CV), and vowelconsonant (VC)] pronounced by one male and one female speakers for 3 normal hearing (NH) and 3 CI adults with 9 low-pass filtering frequency conditions. Results: Both groups showed decreased correction scores as cut-off frequency getting lower. CI subjects scored twice errors to NH subjects across frequency conditions. The cut-off frequency of 1,500 Hz brought a significant decrease of consonant recognition. Consonants in VCV syllable recognized better than VC and CV syllable in both groups. Fricatives and affricates in the manner of articulation and alveolar and palatal in the place of articulation are the ones that benefit from high frequency coding. Alveolar plosive sounds were most difficult sounds in both groups and this confirms previous studies of consonant recognition in Korean. Conclusion: NH and CI groups demonstrated poorer consonant recognition as cut-off frequency decreased with relatively large decrements of CI group. The information above 3,000 Hz conveys little information for consonant recognition in the normal and CI subjects while some CI subjects utilized information up to 6,000 Hz. There were large individual differences, particularly in CI group.