Interaction between phonemic and prosodic perception in cochlear implant users

Abstract

Because most cochlear implants (CI) are designed and adjusted to enable phonemes in speech to be most efficiently perceived, prosody is perceived poorly and may even interfere with phonemic perception. We studied the effects of (1) Japanese-language pitch accent on phonemic perception and (2) the presentation level on the perception of phonemes and pitch accents, with word intelligibility tests in three postlingually deaf CI patients (N24, SPEAK). Two-syllabic Japanese words were presented with either low-high or high-low pitch accent at +10, 0, -10, and -15/-20dB relative to the most comfortable level (MCL). Results showed that the same phonemes were heard differently depending on the accent type or the presentation level, suggesting an interaction between phonemic and prosodic perception. Different types of pitch accent were found to affect phoneme perception differentially at MCL or higher. Phonemic perception improved as the presentation level increased, whereas the performance of pitch accent identification was similar across all levels. These results suggest that postimplantation training should explicitly incorporate prosodic factors to improve overall speech intelligibility.