Contrastive stress production by children with cochlear implants: Accuracy and acoustic characteristics

Mandarin-speaking Children With Cochlear Implants Face Challenges in Using F0 Expansion to Express Contrastive Focus

OBJECTIVES

Children with cochlear implants (CIs) face challenges in perceiving fundamental frequency (F0) information because CIs do not transmit F0 effectively. In Mandarin, F0 can contrast meanings at the word level, that is, via lexical tones with distinct F0 contours, and signal contrastive relations between words at the utterance-level, that is, via contrastive focus with expanded F0 range and longer duration. Mandarin-speaking children with CIs have been reported to face challenges in producing distinct F0 contours across tones, but early implantation facilitates tonal acquisition. However, it is still unclear if utterance-level prosody, such as contrastive focus, is also challenging for these children, and if early implantation also offers benefits for focus production. Therefore, this study asked how accurately children with CIs can produce contrastive focus, and if early implantation leads to more accurate focus production, with acoustic patterns approaching that of children with typical hearing (TH).

DESIGN

Participants included 55 Mandarin-speaking children (3 to 7 years) with CIs and 55 age-matched children with TH. Children produced noun phrases with and without contrastive focus, such as RED-COLORED cat versus red-colored cat . Three adult native listeners perceptually scored the productions as correct or incorrect. The "correct" productions were then acoustically analyzed in terms of F0 range and duration.

RESULTS

Based on the perceptual scores, children with CIs produced focus with significantly lower accuracy (38%) than their TH peers (84%). The acoustic analysis on their "correct" productions showed that children with TH used both F0 and duration to mark focus, producing focal syllables with an expanded F0 range and long duration, and postfocal syllables with a reduced F0 range and short duration. However, children with CIs differed from children with TH in that they produced focal syllables with long duration but not an expanded F0 range, although they produced postfocal syllables with a reduced F0 range and short duration like their TH peers. In addition, early implantation correlated with the percept of more accurate focus productions and better use of F0 range in focal marking.

CONCLUSIONS

This study finds that Mandarin-speaking children with CIs are still learning to apply appropriate acoustic cues to contrastive focus. The challenge appears to lie in the use of an expanded F0 range to mark focus, probably related to the limited transmission of F0 information through the CI devices. These findings thus have implications for parents and those working with children with CIs, showing that utterance-level prosody also requires speech remediation, and underscores the critical role of identifying problems early in the acquisition of F0 functions in Mandarin, not only at the word level but also at the utterance-level.

A meta-analysis of expressive prosody in cochlear implant users

INTRODUCTION

Prosody is used to express indexical (identifying the talker), linguistic (e.g., question intonation, lexical stress), pragmatic (e.g., contrastive stress, sarcasm), and emotional/affective functions. It is manifested through changes in fundamental frequency (f0), intensity, and duration. F0 and intensity are degraded when perceived through a cochlear implant (CI). The purpose of this meta-analysis is to compare expressive prosody in speech produced by CI users versus normal hearing peers.

METHODS

A systematic search of the literature found 25 articles that met all inclusion criteria. These articles were assessed for quality, and data pertaining to the expression of f0, intensity, and duration, as well as classification accuracy and appropriateness ratings from normal hearing listeners, were extracted and meta-analyzed using random effects models.

RESULTS

The articles included in the meta-analysis were generally of acceptable or high quality. Meta-analyses revealed significant differences between individuals with CIs vs. normal hearing on all measures except mean f0, mean intensity, and rhythm. Effect sizes were generally medium to large. There was significant heterogeneity across studies, but little evidence of publication bias.

CONCLUSIONS

CI users speak with less variable f0, smaller f0 contours, more variable intensity, a slower speech rate, and reduced final lengthening at syntactic boundaries. These acoustic differences are reflected in significantly poorer ratings of speech produced by CI users compared to their normal hearing peers, as assessed by groups of normal hearing listeners. Because atypical expressive prosody is associated with negative outcomes, clinicians should consider targeting prosody when working with individuals who use CIs.

Strategic perceptual weighting of acoustic cues for word stress in listeners with cochlear implants, acoustic hearing, or simulated bimodal hearing

Perception of word stress is an important aspect of recognizing speech, guiding the listener toward candidate words based on the perceived stress pattern. Cochlear implant (CI) signal processing is likely to disrupt some of the available cues for word stress, particularly vowel quality and pitch contour changes. In this study, we used a cue weighting paradigm to investigate differences in stress cue weighting patterns between participants listening with CIs and those with normal hearing (NH). We found that participants with CIs gave less weight to frequency-based pitch and vowel quality cues than NH listeners but compensated by upweighting vowel duration and intensity cues. Nonetheless, CI listeners' stress judgments were also significantly influenced by vowel quality and pitch, and they modulated their usage of these cues depending on the specific word pair in a manner similar to NH participants. In a series of separate online experiments with NH listeners, we simulated aspects of bimodal hearing by combining low-pass filtered speech with a vocoded signal. In these conditions, participants upweighted pitch and vowel quality cues relative to a fully vocoded control condition, suggesting that bimodal listening holds promise for restoring the stress cue weighting patterns exhibited by listeners with NH.