Production and perception of volitional laughter across social contexts.

Human nonverbal vocalizations such as laughter communicate emotion, motivation, and intent during social interactions. While differences between spontaneous and volitional laughs have been described, little is known about the communicative functions of volitional (voluntary) laughter-a complex signal used across diverse social contexts. Here, we examined whether the acoustic structure of volitional laughter encodes social contextual information recognizable by humans and computers. We asked men and women to produce volitional laughs in eight distinct social contexts ranging from positive (e.g., watching a comedy) to negative valence (e.g., embarrassment). Human listeners and machine classification algorithms accurately identified most laughter contexts above chance. However, confusion often arose within valence categories, and could be largely explained by shared acoustics. Although some acoustic features varied across social contexts, including fundamental frequency (perceived as voice pitch) and energy parameters (entropy variance, loudness, spectral centroid, and cepstral peak prominence), which also predicted listeners' recognition of laughter contexts, laughs evoked across different social contexts still often overlapped in acoustic and perceptual space. Thus, we show that volitional laughter can convey some reliable information about social context, but much of this is tied to valence, suggesting that volitional laughter is a graded rather than discrete vocal signal.