Natural laughter that has nothing artificial, involving the vocal chords, and made with an open mouth, is the most appealing.
The study found 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," Discovery News quoted Michael Owren, an experimental psychologist at Georgia State University in Atlanta, as saying.
"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," Owren added.
To learn more, Owren and colleagues began by recording people as they laughed while either socializing 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 analyzed listeners 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. So 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 said.
Confirming earlier work, listeners also liked female laughter more. He findings suggest that, beginning in childhood, we learn to associate the wide-open guffaw with life's most positive experiences, Owren said. 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. It's a kind of unconscious that we build up throughout life that significantly influences the way we interpret laughter events in everyday social situations," he said.
The study has been reporting this week at the Pan-American/Iberian Meeting on Acoustics in Cancun.