Edited by Susan T. Fiske, Princeton University, Princeton, NJ, and approved March 9, 2016 (received for review December 18, 2015)
Human cooperation requires reliable communication about social intentions and alliances. Although laughter is a phylogenetically conserved vocalization linked to affiliative behavior in nonhuman primates, its functions in modern humans are not well understood. We show that judges all around the world, hearing only brief instances of colaughter produced by pairs of American English speakers in real conversations, are able to reliably identify friends and strangers. Participants’ judgments of friendship status were linked to acoustic features of laughs known to be associated with spontaneous production and high arousal. These findings strongly suggest that colaughter is universally perceivable as a reliable indicator of relationship quality, and contribute to our understanding of how nonverbal communicative behavior might have facilitated the evolution of cooperation.
Laughter is a nonverbal vocal expression that often communicates positive affect and cooperative intent in humans. Temporally coincident laughter occurring within groups is a potentially rich cue of affiliation to overhearers. We examined listeners’ judgments of affiliation based on brief, decontextualized instances of colaughter between either established friends or recently acquainted strangers. In a sample of 966 participants from 24 societies, people reliably distinguished friends from strangers with an accuracy of 53–67%. Acoustic analyses of the individual laughter segments revealed that, across cultures, listeners’ judgments were consistently predicted by voicing dynamics, suggesting perceptual sensitivity to emotionally triggered spontaneous production. Colaughter affords rapid and accurate appraisals of affiliation that transcend cultural and linguistic boundaries, and may constitute a universal means of signaling cooperative relationships.
Author contributions: G.A.B. designed research; G.A.B., R.F., E.C., L.A., C.L.A., M.B.P., S.T.B., A.B., B.C., D.D.S., C.D., J.F., M.F., P.G.-P., A.H., S.V.K., T.K., N.P.L., F.R.L., P.P., K.Q., B.A.S., H.J.S., M.S., S.S., W.T., E.A.v.d.H., H.V.-A., S.E.Y., J.C.Y., T.Y., and Y.Z. performed research; G.A.B. and R.F. analyzed data; G.A.B., D.M.T.F., and R.F. wrote the paper; D.M.T.F. conceived and organized the cross-cultural component; and E.C. coordinated cross-cultural researchers.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: Experimental response data from all study sites and acoustic data from all laugh stimuli are available at https://escholarship.org/uc/item/99j8r0gx.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1524993113/-/DCSupplemental.
