ROBERT SIEGEL, HOST:
And now, strictly in the interests of evolutionary psychology, the nurse asked me to sit down and asked me if I was comfortable and I said, well, I make a living.
(LAUGHTER)
SIEGEL: Now, did that person really find that funny because what we're going to hear about now is laughter. There's new research showing that people can often tell fake laughs from real laughs. Real laughter apparently has a set of unique acoustic features that fake laughs do not fully duplicate so people can often tell the difference between this...
(SOUNDBITE OF LAUGH)
SIEGEL: ...and this.
(SOUNDBITE OF LAUGH)
SIEGEL: But which is which? Greg Bryant of UCLA is going to tell us. He is an evolutionary psychologist and he is co-author of this study. Welcome to the program.
GREG BRYANT: Thank you.
SIEGEL: I just played two laughs from your study. Let's hear the first one again.
(SOUNDBITE OF LAUGH)
SIEGEL: Is that a real laugh or a fake laugh?
BRYANT: That, in our study, was a real laugh.
SIEGEL: Real laugh. Meaning?
BRYANT: Meaning that we recorded it in a conversation between two friends, as opposed to our fake laughs, which we asked people to produce on command.
SIEGEL: OK. Let's hear our fake laugh again.
(SOUNDBITE OF LAUGH)
SIEGEL: Now, if you played those two laughs and this is, I gather, what your study was, you played them for a number of people, how commonly could people say the first one was a genuine, authentic expression of humor and the second was a fake?
BRYANT: Right. So we played people both fake laughs and real laughs and when the correct answer was a real laugh, they got that correct answer over two-thirds of the time. But when they heard fake laughs, they also thought sometimes those were real so they were tricked about a third of the time.
SIEGEL: So there are false positives when it comes to fake laughs.
BRYANT: That's right.
SIEGEL: I see. And what is it? How do you figure it is that we somehow know or so many of us know that a laugh is not genuine?
BRYANT: Well, I think there are a number of acoustic features that people unconsciously pay attention to, things like higher pitch and loudness, but there also seems to be something that has to do with the breathing. In a real laugh, the proportion of breathiness to valve sound is higher. So there's more breathiness in a real laugh than there is in a fake laugh.
And we believe that that has to do with the fact that laughs are produced by different vocal systems so genuine laughs are produced by an emotional vocal system that we share with other animals and fake laughs are produced by the speech system which is human specific.
SIEGEL: Which is human specific.
BRYANT: Right.
SIEGEL: But a really good actor, you know, who could tell himself a great joke, a method actor would be able to do a convincing fake laugh, wouldn't he?
BRYANT: Right. That's a great question. I think that when people are able to use something like method acting, they are producing what I would call a real laugh. So people can sort of conjure up the real thing. I actually don't like the terminology real and fake, technically, because I think all laughs are real at some level.
But the question is, which vocal system is actually producing it.
SIEGEL: So really, what we're distinguishing between here are fake laughs and on the one hand and real and really good fake laughs on the other hand.
BRYANT: Right. Well, yeah, so there's emotional laughs. There are good fake laughs and there are bad fake laughs.
SIEGEL: Laughter is not your only academic interest. You've researched many things. But is there more to do with laughs?
BRYANT: Absolutely. I'm working on some studies showing that people can recognize if people laughing together know each other or not and I'm also interested in various kinds of laughs. So for example, I think that laughs generated when somebody's being tickled, those are different than polite laughs in conversation.
SIEGEL: I can only imagine the experiment that's coming to test that one.
BRYANT: Right.
SIEGEL: Well, Professor Bryant, thank you very much for talking with us about laughs.
BRYANT: Thanks for having me.
SIEGEL: That's Greg Bryant. He's associate professor of communication studies at UCLA. His study appears in the journal Evolution and Human Behavior. Transcript provided by NPR, Copyright NPR.