MARY LOUISE KELLY, HOST:
Psychologists have long pondered the meaning of laughter, and more recently, they've asked what it tells us about the relationship between people.
GREG BRYANT: Can people make accurate judgments about whether a pair of people laughing together - whether they are friends or strangers?
AUDIE CORNISH, HOST:
That's Greg Bryant, a cognitive scientist at UCLA. A few years back he took that question worldwide, playing snippets of friends laughing or strangers laughing to everyone from hunter-gatherers to college students. And across 24 cultures, he found that people could tell friends and strangers apart merely by the sound of their laughter.
KELLY: OK, so pop quiz - let's see if you all can pass the test. Here is one sample...
(LAUGHTER)
KELLY: ...And the other.
(LAUGHTER)
KELLY: If you guessed the second pair to be friends, you would be right.
CORNISH: Well, now Bryant's team has asked, what about speech? Does that also telegraph friendship? Here's sample one.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #1: It's like - and you know they're wrong.
UNIDENTIFIED PERSON #2: And then...
UNIDENTIFIED PERSON #1: It's like, no.
UNIDENTIFIED PERSON #2: Yeah.
CORNISH: All right - and the other.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #3: Some chalupa...
UNIDENTIFIED PERSON #4: Yeah.
UNIDENTIFIED PERSON #3: ...Or something...
UNIDENTIFIED PERSON #4: Because they scored a hundred points.
UNIDENTIFIED PERSON #3: Yes.
CORNISH: The first speakers were friends, but it's a bit harder to tell.
KELLY: In fact, Bryant's new study, published this week by the Royal Society, found that the hundred study volunteers were significantly better at differentiating friends from strangers when eavesdropping on laughter rather than speech.
BRYANT: In this particular study, the samples of speech were about twice as long as the laughter, and they still weren't as good.
CORNISH: There is an evolutionary reason for this, says Adrienne Wood of the University of Virginia. She says laughter is a, quote, "play signal," which tells those around us that we have harmless intentions. Other animals do it, too.
ADRIENNE WOOD: Many mammals have evolved this vocalization that is kind of an early version of human laughter that is this rapid panting.
KELLY: And based on these new findings, Bryant suspects laughter is meant to be overheard.
BRYANT: When people are laughing together, they are consciously producing a signal that is actually designed for broadcast. Overhearers can detect something about their social alliance through the way they laugh together.
CORNISH: Of course, given our new social arrangements - stuck at home, seeing less of friends - laughter may be harder to come by. But Wood says we need to keep up the practice.
WOOD: Laughter is a social experience. So if you're living alone right now, watching a funny movie is not going to get you to laugh necessarily. So maybe try doing, like, a Netflix party or something where you could laugh with other people because it's really good for you.
KELLY: All right. OK, Audie, what do you say - virtual Netflix party this weekend?
CORNISH: Yeah, I mean, as long as I get to pick the movie.
KELLY: (Laughter).
(SOUNDBITE OF BROKE FOR FREE'S "ADD AND") Transcript provided by NPR, Copyright NPR.