Abstract
There is a wide range of acoustic and visual variability across different talkers and different speaking contexts. Listeners with normal hearing (NH) accommodate that variability in ways that facilitate efficient perception, but it is not known whether listeners with cochlear implants (CIs) can do the same. In this study, listeners with NH and listeners with CIs were tested for accommodation to auditory and visual phonetic contexts created by gender-driven speech differences as well as vowel coarticulation and lip rounding in both consonants and vowels. Accommodation was measured as the shifting of perceptual boundaries between /s/ and /∫/ sounds in various contexts, as modeled by mixed-effects logistic regression. Owing to the spectral contrasts thought to underlie these context effects, CI listeners were predicted to perform poorly, but showed considerable success. Listeners with CIs not only showed sensitivity to auditory cues to gender, they were also able to use visual cues to gender (i.e., faces) as a supplement or proxy for information in the acoustic domain, in a pattern that was not observed for listeners with NH. Spectrally-degraded stimuli heard by listeners with NH generally did not elicit strong context effects, underscoring the limitations of noise vocoders and/or the importance of experience with electric hearing. Visual cues for consonant lip rounding and vowel lip rounding were perceived in a manner consistent with coarticulation and were generally used more heavily by listeners with CIs. Results suggest that listeners with CIs are able to accommodate various sources of acoustic variability either by attending to appropriate acoustic cues or by inferring them via the visual signal.
Highlights
Variability in the acoustic realization of speech segments is a well-known phenomenon that can arise from several sources, including coarticulation with neighboring segments and intertalker differences related to gender and vocal tract size
To the extent that these effects are representative of the many inter-talker and cross-context variations present in natural speech, successful accommodation appears to emerge without fine spectral resolution
The 50% crossover point in /s/-/ / identification in each context was calculated from the group aggregate GLMMs in both experiments
Summary
Variability in the acoustic realization of speech segments is a well-known phenomenon that can arise from several sources, including coarticulation with neighboring segments and intertalker differences related to gender and vocal tract size. Despite this variability in the physical properties of the signal, normal hearing (NH) listeners are remarkably successful at perceiving and understanding speech. Acoustic simulations of CI processing confirm, that NH listeners can understand speech with a high degree of accuracy even when signals are spectrally degraded (Shannon et al, 1995; Friesen et al, 2001). Perceptual weighting for phonetic cues decreases in the spectral domain and increases in the temporal domain for listeners with CIs or for NH www.frontiersin.org
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