When you laugh, the whole world laughs with you - as long as your sentiment is genuine, your vocal cords are engaged, and your mouth is open.
A new study has that people experienced the most positive emotional reactions when they heard spontaneous, open-mouthed laughter, especially if the laughter came from a woman. Breathy laughter made with a closed mouth didn't elicit the same good feelings.
The finding adds to a growing understanding of how laughing functions as a deeply rooted form of unconscious communication between people.
By studying the nuances of laughter sounds, researchers may also eventually figure out how to design computers that can produce the right kinds of laughter in the right kinds of situations.
"I think of laughter sounds as a kind of fundamental mechanism for building up and maintaining positive social relationships," says Associate Professor Michael Owren, an experimental psychologist at Georgia State University in Atlanta.
"Laughter is almost a dominant feature in social interactions. It clearly has some role in promoting positive emotional bonds. But it's not clear how that's working."
To learn more, Owren and colleagues began by recording people as they laughed while either socialising in a happy way or watching funny videos. The team kept only examples of laughter that was associated with positive feelings, and they separated the clips into short bursts of sound that featured either open-mouthed or closed-mouthed laughing.
From previous work that analysed listener's emotions through subtle movements in their faces, the researchers knew that people respond more positively to voiced laughter, which engages the vocal chords in a "ha-ha" kind of way, than to unvoiced laughter, which involves more of a panting sound.
In the new experiment, all of the clips included only voiced laughter.
When a group of 28 people listened to nearly 50 bouts of the recorded clips, they gave the most positive ratings to open-mouthed laughter, Owren is reporting this week at the Pan-American/Iberian Meeting on Acoustics in Cancun. Confirming earlier work, listeners also liked female laughter more.
The findings suggest that, beginning in childhood, we learn to associate the wide-open guffaw with life's most positive experiences, says Owren. Eventually, all it takes is to hear that happy sound to feel happier.
"We suspect that we all as listeners have learned emotional responses to laughter sounds that have different kinds of acoustic cues," he says. "It's a kind of unconscious [response] that we build up throughout life that significantly influences the way we interpret laughter events in everyday social situations."
From a practical view, he says, scientists will need to understand how different laughter sounds elicit different emotions in order to ever have hope of programming computers that can respond appropriately in social settings.
Laughter is universal
The study also fleshes out our understanding of laughter as a staple of human behaviour, with roots that precede humanity, says Robert Provine, a neuroscientist at the University of Maryland, Baltimore County, and author of Laughter: A Scientific Investigation.
Chimpanzees sound like they're panting when they play, he said. As our ancestors developed speech, "pant-pant" became "ha-ha," and human laughter was born.
Today, laughter is ubiquitous in human societies and there is laughter in most social interactions. Whether forced or real, laughter clearly serves a social purpose, says Provine, occurring 30 times less often when we're alone than when we're with others.
Despite individual variations in voice and style, laughter also follows consistent patterns from person to person and place to place, hinting as something very deep and universal.
In his work, for example, Provine has found that most bouts of laughter occur in short bursts that last for about one-fifteenth of a second and repeat every one-fifth of a second.
"We're dealing here with something at the bedrock of human nature that all people have in common," he says "While there are thousands of languages and hundreds of dialects, everyone speaks laughter in much the same way."