Laughter is a nonverbal vocal expression that often communicates positive affect and cooperative intent in humans. A laugh may signal mockery, humor, joy or simply be a response to tickling, but each kind of laughter conveys a wealth of auditory and social information. Researchers have distinguished between spontaneous and volitional laughter. Spontaneous laughter is emotionally-driven and involuntary (i.e., laughter produced in natural contexts between familiar speakers) while volitional, is non-emotional and articulated laughter (i.e laughter produced on command, inarguably deliberate and controlled).
Just one second laughter between people is enough to judge whether there exist friendship or not. This was a UCLA study published in the proceedings of National Academy of Sciences.
In past research, Bryant who is a co-author in this research, has investigated the idea that listeners can tell the difference between involuntary, or spontaneous, laughter and volitional, or “fake,” laughter. His findings indicate that the different kinds of laughs are produced by different vocal systems and that they have different communicative functions.
The scenario used in this research was the one in which listeners were best able to judge or gauge the relationship correctly was when two women friends were laughing together. The study suggests that laughter between friends is generally more spontaneous, and that listeners across the globe can hear the difference. To detect the relationship status among people, spontaneous and volitional laughter are produced by different underlying neural control systems, with spontaneous laughter generated by phylogenetically older vocal production mechanisms. The laugh types were acoustically distinct, and differentially judged in a predictable way according to manipulations of duration properties. The slowed down spontaneous laughs were perceptually indistinguishable from non-human animal vocalizations.
In a highly cooperative species such as ours, it is important for individuals to correctly identify the social alliances of others,” Bryant said. “If laughter helps people accomplish that, it has likely played a role in social communication leading to cooperative interactions.