A new study published on Monday suggests that the laughter we share with our friends sounds different from the laughter we share with strangers. That enables onlookers to judge the type of relationship the laughing people have, Dr. Greg Bryant, professor of communication studies at the University of California and lead author of the study, told The Huffington Post. “Laughter between friends is often faster, louder and longer,” he said.

     The researchers played 48 short audio clips(音频片段) of two people laughing for 966 volunteers representing 24 different cultural backgrounds, including remote hunter-gatherer communities. Some of the recordings were of two recently acquainted(认识的) strangers, while the others were of two friends. The pairs could be two men, two women, or a man and a woman. The volunteers were asked to listen and identify which laughing pairs were friends and which were strangers.

     “The volunteers correctly identified whether the people were friends or strangers 61 percent of the time. Their accuracy rate reached 83 percent when the two people were female friends,” Bryant said. “But it fell to 44 percent when the two women were strangers.”

      “While the researchers had predicted that people in all cultures would be able to distinguish between friends and strangers,” he said. “We didn’t expect specifically that women friends would be reliably judged best in every society.”

    The study indicates how universal the perception of vocal emotions can be in Bryant’s words. The researchers noted that it also highlights one way laughter allows us to communicate social information indirectly.

   “Laughter may be a simple behavior, but it’s also a powerful tool that provides insight into more complicated(复杂的) vocalizations, like speech and language. The study shows how even in the most remote places on our planet, a laugh among friends is a special sound,” Dr. Robert R. Provine, a neuroscientist at the University of Maryland said.