Belyk, Michel;
McGettigan, Carolyn;
(2022)
Real-time magnetic resonance imaging reveals distinct vocal tract configurations during spontaneous and volitional laughter.
Philosophical Transactions of the Royal Society B: Biological Sciences
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Abstract
A substantial body of acoustic and behavioural evidence points to the existence of two broad categories of laughter in humans: spontaneous laughter that is emotionally genuine and somewhat involuntary, and volitional laughter that is produced on demand. In this study, we tested the hypothesis these are also physiologically distinct vocalisations, by measuring and comparing them using real-time MRI (rtMRI) of the vocal tract. Following Ruch & Ekman (2001), we further predicted that spontaneous laughter should be relatively less speech-like (i.e. less articulate) than volitional laughter. We collected rtMRI data from five adult human participants during spontaneous laughter, volitional laughter, and spoken vowels. We report distinguishable vocal tract shapes during the vocalic portions of these three vocalisation types, where volitional laughs were intermediate between spontaneous laughs and vowels. Inspection of local features within the vocal tract across the different vocalisation types offers some additional support for Ruch and Ekman’s (2001) predictions. We discuss our findings in light of a dual-pathway hypothesis for the neural control of human volitional and spontaneous vocal behaviours, identifying tongue shape and velum lowering as potential biomarkers of spontaneous laughter to be investigated in future research.
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