Abstract
Humans have a remarkable capacity to finely control the muscles of the larynx, via distinct patterns of cortical topography and innervation that may underpin our sophisticated vocal capabilities compared with non-human primates. Here, we investigated the behavioural and neural correlates of laryngeal control, and their relationship to vocal expertise, using an imitation task that required adjustments of larynx musculature during speech. Highly trained human singers and non-singer control participants modulated voice pitch and vocal tract length (VTL) to mimic auditory speech targets, while undergoing real-time anatomical scans of the vocal tract and functional scans of brain activity. Multivariate analyses of speech acoustics, larynx movements and brain activation data were used to quantify vocal modulation behaviour and to search for neural representations of the two modulated vocal parameters during the preparation and execution of speech. We found that singers showed more accurate task-relevant modulations of speech pitch and VTL (i.e. larynx height, as measured with vocal tract MRI) during speech imitation; this was accompanied by stronger representation of VTL within a region of the right somatosensory cortex. Our findings suggest a common neural basis for enhanced vocal control in speech and song. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.
Highlights
Many cognitive, neural and physiological adaptations have been implicated in the evolution of human speech [1,2,3]
ΔF is related to the resonant properties of the vocal tract and covaries negatively with vocal tract length (VTL)—adults show lower ΔF than children, and adult male voices typically have lower ΔF than adult female voices owing to the secondary descent of the larynx during puberty in human males
When participants were asked to move the larynx vertically, without speaking, the investigators observed extensive activation covering the ventrolateral sensorimotor cortex in both hemispheres, which included the dorsal larynx motor cortex (LMC). Our results extend this finding, as we show that the post-central gyrus houses representations of VTL during speech that are associated with expertise-related group differences in voice modulation through larynx movement
Summary
Neural and physiological adaptations have been implicated in the evolution of human speech [1,2,3]. As F0 and VTL typically covary negatively across human voices (i.e. adult males have longer VTLs and lower pitches than adult females and children), we predicted that including atypical combinations of voice parameters (e.g. short VTL with lowered pitch; long VTL with raised pitch) should add difficulty to the task Both design choices were made to maximize the discriminability of expert versus non-expert vocal control. Using multivariate analyses of behaviour and neural activation (representational similarity analysis, RSA; [40]) during speech preparation and execution, we aimed to measure imitation accuracy and locate the representation of pitch/vocal fold tension and VTL/larynx height during the two phases of speech imitation. We predicted that expertise in singing would generalize to greater speech imitation accuracy in the singers, and reveal more robust corresponding neural representations of laryngeal activity in this group
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