You can tell more about people’s relationships by listening to their laughter than from hearing their voices, a study finds.

Snippets of recorded laughter and conversations were played to a group of people that didn’t know the subjects.

And although the speaking clips were twice as long as the laughing ones, the listeners were able to identify whether the interactions were taking place between friends or strangers more accurately through the laughter.

Even just a second or two of laugher was usually enough to convey whether people were close or newly acquainted, the study found.

Loud and conspicuous

Laughter is far more effective at quickly communicating the state of two or more people’s emotional signals than speech because it is loud, conspicuous and contagious, the researchers said.

In that sense laughter is more like extreme emotional signals such as crying or screams than speaking, which are also elicit a rapid reaction, over relatively long distances.

“Laughter is generated by an evolutionarily old brain system. It acts as a signal of emotion and intention, providing rich information about speaker engagement,” said Greg Bryant, of the University of California at Los Angeles.

“A belly laugh or other really exuberant laugh would do the trick for sure, but the laughs we used were not quite like that. Examples between friends just have a slightly more excited sound to them, again, likely because friends are often more aroused together than strangers. And the reserved, forced laughs of strangers will contribute to the contrast,” he said.

Chorused signal

“We make the case that people ‘colaughing’ are, at some level, often producing a ‘chorused signal’ for others outside of the group. It’s below our awareness, but the signal can function that way without us realising it.”

“People are adept at making affiliation judgments from colaughter and only need a second of it. But listeners need much more speech to make the comparably accurate judgment.”

“Broadcasting the situation through laughter could serve to influence how outsiders might interact with that group. This can include encouraging interaction in some contexts, for example by inviting others to join. Or by discouraging it,” he said.

The study is published in the journal Royal Society Open Science.