People can catch a 'fake laugh', according to a new study which found that listeners seem to pay attention to certain acoustic features of genuine laughter that are really hard to feign.
New research from the University of California - Los Angeles found that people can fool others by pretending to laugh at their jokes just over one-third of the time.
When your fake laughs fall short of convincing, tiny subtleties of your breathing are probably giving you away, said Greg Bryant, an associate professor of communication studies at UCLA.
"Quite a few fake laughs sound pretty good, but listeners seem to pay attention to certain acoustic features that are really hard to fake," he said.
For the study, published in the journal Evolution and Human Behavior, Bryant recorded the spontaneous conversations of college roommates. From these recordings, he collected 18 spontaneous laughs, which he considered to be genuine.
He then enlisted a different group of co-eds to laugh on command. From this exercise, he recorded 18 fake laughs of the same length as the real ones.
With Athena Aktipis, a research scientist at UC San Francisco, he then played the recordings to three groups of UCLA undergraduates.
In the first round, the participants were asked to determine whether the laughs were real or fake, and the students could usually tell the difference. But they were fooled by 37 per cent of the fake laughs.
In the second round, the researchers sped up the recordings and played them to a different group of college students. Speeding up the laughter significantly increased the likelihood that both kinds of laughs were judged as genuine, the researchers found.
When sped up, the fake laughs fooled the study subjects half the time.
Bryant and Aktipis then dramatically slowed down the recordings and played them to yet another group of participants. The researchers asked the students to figure out whether the sounds were made by humans or nonhuman animals.
The students couldn't tell whether genuine laughs were human or not, but they could tell that the fake laughs were made by people.
Bryant believes that the research illustrates that the two types of laughs - real and fake - are made by two separate vocalisation systems.
"Genuine laughs are produced by an emotional vocal system that humans share with all primates, whereas fake laughs are produced by a speech system that is unique to humans,"