Native Mandarin normal-hearing (NH) listeners can easily perceive lexical tones even under conditions of great voice pitch variations across speakers by using the pitch contrast between context and target stimuli. It is however unclear whether cochlear implant (CI) users with limited access to pitch cues can make similar use of context pitch cues for tone normalization. In this study, native Mandarin NH listeners and pre-lingually deafened unilaterally implanted CI users were asked to recognize a series of Mandarin tones varying from Tone 1 (high-flat) to Tone 2 (mid-rising) with or without a preceding sentence context. Most of the CI subjects used a hearing aid (HA) in the non-implanted ear (i.e., bimodal users) and were tested both with CI alone and CI+HA. In the test without context, typical S-shaped tone recognition functions were observed for most CI subjects and the function slopes and perceptual boundaries were similar with either CI alone or CI+HA. Compared to NH subjects, CI subjects were less sensitive to the pitch changes in target tones. In the test with context, NH subjects had more (resp. fewer) Tone-2 responses in a context with high (resp. low) fundamental frequencies, known as the contrastive context effect. For CI subjects, a similar contrastive context effect was found statistically significant for tone recognition with CI+HA but not with CI alone. The results suggest that the pitch cues from CIs may not be sufficient to consistently support the pitch contrast processing for tone normalization. The additional pitch cues from aided residual acoustic hearing can however provide CI users with a similar tone normalization capability as NH listeners.

Objectives For cochlear implant (CI) users with residual low-frequency acoustic hearing in the non-implanted ear, bimodal hearing combining the use of a CI and a contralateral hearing aid (HA) may provide more salient talker voice cues than CI alone to handle the variability of talker identity across trials. This study tested the effects of talker variability, bimodal hearing, and their interaction on response accuracy and time of CI users’ Mandarin tone, vowel, and syllable recognition (i.e., combined Mandarin tone and vowel recognition in this study). Design Fifteen prelingually deafened native Mandarin-speaking CI users (at age 20 or lower) participated in this study. Four talkers each produced six Mandarin single-vowel syllables in four lexical tones. The stimuli were presented in quiet via a single loudspeaker. To study the effects of talker variability, Mandarin tone, vowel, and syllable recognition was tested in two presentation conditions: with stimuli blocked according to talker (blocked-talker condition) or mixed across talkers from trial to trial (mixed-talker condition). To explore the effects of bimodal hearing, two processor conditions were tested: CI alone or CI+HA. The cumulative response time was recorded as an indirect indicator of the cognitive load or listening effort in each condition. The correlations were computed between demographic/hearing factors (e.g., hearing thresholds in the non-implanted ear) and bimodal performance/benefits (where bimodal benefits refer to the performance differences between CI alone and CI+HA). Results Mandarin tone recognition with both CI alone and CI+HA was significantly poorer in the mixed-talker condition than in the blocked-talker condition, while vowel recognition was comparable in the two presentation conditions. Bimodal hearing significantly improved Mandarin tone recognition but not vowel recognition. Mandarin syllable recognition was significantly affected by both talker variability and bimodal hearing. The cumulative response time significantly reduced with CI+HA compared with CI alone, but remained invariant with respect to talker variability. There was no interaction between talker variability and bimodal hearing for any performance measure adopted in this study. Correlation analyses revealed that the bimodal performance and benefits in Mandarin tone, vowel, and syllable recognition could not be predicted by the hearing thresholds in the non-implanted ear or by the demographic factors of the participants. Conclusions Talker variability from trial to trial significantly degraded Mandarin tone and syllable recognition performance in both the CI alone and CI+HA conditions. While bimodal hearing did not reduce the talker variability effects on Mandarin tone and syllable recognition, generally better Mandarin tone and syllable recognition performance with shorter response time (an indicator of less listening effort) was observed when a contralateral HA was used in conjunction with the CI. On the other hand, vowel recognition was not significantly ...

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