Categorical Perception in Two Pairs of Mandarin Tones among Bimodal Cochlear Implanted Children

We investigated the categorical perception for two tone-pairs in Mandarin (T1-T2 and T1-T4) by two groups of 4-5 year-old children - normal-hearing (NH) children and hearing-impaired children with bimodal cochlear implants/hearing aids. The perceptual identification tests using two sets of synthetic speech stimuli varying only along F-0 continua were administered. Both the hearing and Cochlear Implant (CI) groups showed categorical effects in the two identification tests, but the category boundaries in the CI group were more biased toward T2 (rising tone) or T4 (falling tone) than was observed in the NH group. This finding suggests that the children with CIs are perceptually less sensitive to contour tones with dynamic pitch movements. For the CI group, the categorical effect was slightly stronger than the NH group in perceiving the T1-T4 continuum, but was weaker than the NH group in perceiving the T1-T2 continuum, suggesting that the children with CIs had particular difficulty in perceiving pitch distinction between the level and rising tones.