Everybody loves a good laugh, but not all laughs are created equal. Sharing a laugh with friends sounds different than laughing with strangers—and a new study shows that people all over the world are surprisingly good at telling which laugh is which from even the briefest exposure to the sound.
Researchers asked 966 individuals from 24 societies scattered across the globe to listen to brief recordings of pairs of people laughing together for about one second. Some of those pairings matched two friends, but others were strangers. Most listeners, 61 percent overall, proved reliably good at identifying who were friends and who were not from only the sounds of their laughter.
“Laughing isn't necessarily just about communication between the people who are laughing, but potentially it might be a signal to outsiders that gives them some information,” says Greg Bryant, a cognitive psychologist at the University of California, Los Angeles Center for Behavior, Evolution and Culture, and a coauthor on the study published today in the Proceedings of the National Academy of Sciences. “A group of people laughing at a bar might be producing a chorus of signals to others without really being aware of it.”
The results of the study may shed light on laughter’s role as one of the nonverbal communication behaviors that may have helped to drive the evolution of cooperative human societies, Bryant and his colleagues suggest. Laughter may help newcomers or outsiders who hear it to make quick judgments about the status and affiliation of individuals within small groups, the researchers say.
“Laughter may be a simple behavior, but it's also a powerful tool that provides insight into more complicated and difficult vocalizations, like speech and language,” says Robert R. Provine, a neuroscientist at the University of Maryland, Baltimore County, and author of Curious Behavior: Yawning, Laughing, Hiccupping, and Beyond. Studies of laughter can provide a simple systems approach to unlocking aspects of human behavior, he says.
How did so many listeners tell friends and strangers apart? Very careful listening was the key, along with subconscious recognition of what friends sound like when together.
There are “different acoustic features that are associated with arousal [between friends], which is also associated with spontaneous laughter—as opposed to what you might consider a more fake laugh,” Bryant says. Features such as greater variability in loudness and pitch were among the tip-offs. “The laughs are different,” he explains. “Generally, people are more aroused when they produce spontaneous laughs. That's what the listeners were hearing, and they associated that with people who know each other.”
The laughs were snippets extracted from conversations between several pairs of California college students who were recorded in 2003 for a study on ironic speech. This ensured that all the laughs were part of natural conversations and nobody was asked to chuckle on cue. The laughers also had no idea that their giggles and guffaws specifically would someday be the focus of study by an international group of researchers.
Listeners included diverse groups from across the globe, including Tanzania's Hadza people, rural Peruvians and university-educated Europeans and Egyptians.
The study's cross-cultural nature is particularly important, Provine notes. “With laughter you're looking at a human universal, a behavior that's shared by all members of our species,” he says. “To make generalizations about laughter, we need information about its use in different cultures so that we can see that laughter doesn't have one meaning in one society and another in a different society.”
“Given the fact that they found these results across 24 societies, including among individuals who weren't even English speakers like the recorded subjects were, coming up with numbers like this is impressive,” Provine adds.
Yet the ability of listeners to correctly identify the laughers' relationships was better for some pairings of laughers and listeners than others. “When both of the speakers were females, and they were friends, people's accuracy in recognizing the correct answer was close to 80 percent,” Bryant says. In the United States, where the speakers originated, listeners were able to identify the laughers as friends 95 percent of the time. Female strangers, on the other hand, proved particularly difficult to interpret for all societies—participants correctly guessed the laughers’ relationship less than half the time, meaning simply flipping a coin would have been more accurate.
What might account for this discrepancy? It's just one of the questions the research raises, but Bryant has some ideas.
“It probably has something to do with people's assumptions about females laughing together,” he says. Listeners “take that as a more reliable cue that they are actually friends. There's some evidence that females tend to take longer to develop a relationship where they do laugh together, so on some level, people may intuitively know that."
Laughter is important to relationships because it's one of the most social of all human vocalizations, Provine adds. “Recent research has indicated that laughter occurs 30 times more often in social situations then in solitary ones,” he notes. “When you're alone, laughter basically disappears.”