Abstract
Several authors have recently presented evidence for perceptual and neural distinctions between genuine and acted expressions of emotion. Here, we describe how differences in authenticity affect the acoustic and perceptual properties of laughter. In an acoustic analysis, we contrasted spontaneous, authentic laughter with volitional, fake laughter, finding that spontaneous laughter was higher in pitch, longer in duration, and had different spectral characteristics from volitional laughter that was produced under full voluntary control. In a behavioral experiment, listeners perceived spontaneous and volitional laughter as distinct in arousal, valence, and authenticity. Multiple regression analyses further revealed that acoustic measures could significantly predict these affective and authenticity judgements, with the notable exception of authenticity ratings for spontaneous laughter. The combination of acoustic predictors differed according to the laughter type, where volitional laughter ratings were uniquely predicted by harmonics-to-noise ratio (HNR). To better understand the role of HNR in terms of the physiological effects on vocal tract configuration as a function of authenticity during laughter production, we ran an additional experiment in which phonetically trained listeners rated each laugh for breathiness, nasality, and mouth opening. Volitional laughter was found to be significantly more nasal than spontaneous laughter, and the item-wise physiological ratings also significantly predicted affective judgements obtained in the first experiment. Our findings suggest that as an alternative to traditional acoustic measures, ratings of phonatory and articulatory features can be useful descriptors of the acoustic qualities of nonverbal emotional vocalizations, and of their perceptual implications.

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Notes
To avoid multicollinearity being present in the dataset, only F0 mean, F0 variability, total duration, burst duration, percentage of unvoiced segments, harmonics-to-noise ratio, spectral center of gravity and intensity were used in the regression.
Only 4 trained listeners completed the mouth opening scale.
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Acknowledgments
We would like to thank Gary McKeown and one anonymous reviewer for thoughtful and constructive comments on earlier versions of the manuscript. Stimulus recording and data collection for Experiment 1 was supported by a Wellcome Trust Senior Research Fellowship (WT090961MA) awarded to Sophie Scott.
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Lavan, N., Scott, S.K. & McGettigan, C. Laugh Like You Mean It: Authenticity Modulates Acoustic, Physiological and Perceptual Properties of Laughter. J Nonverbal Behav 40, 133–149 (2016). https://doi.org/10.1007/s10919-015-0222-8
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DOI: https://doi.org/10.1007/s10919-015-0222-8