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.