Laughter Between Friends Has Its Own Unique Sound

Photo: Colin Hawkins/Getty Images

Social psychology can be a cruel thing sometimes, casting doubt on the veracity of our friendships (did you know, for example, that half the people you consider friends probably don’t feel the same way?) and leaving us to question whether we’re really as fun, or funny, as we think we are (another fun fact: Most people are pretty bad at spotting fake laughter).

In a recent column in The Wall Street Journal, writer Robert M. Sapolsky offered up a feel-good finding from the field, one that may help those other two truth bombs go down a little easier: Laughter between friends has its own special acoustical signature.

The observation comes from a study published earlier this year in the Proceedings of the National Academy of Sciences that examined listeners’ perceptions of two or more people sharing a laugh, or what the researchers called “co-laughter”:

The researchers prompted college volunteers with topics likely to produce laughter (such as bad roommate experiences) and then had pairs of the students chat. The researchers recorded the conversations and identified instances of co-laughter. Crucially, half the pairs were friends and half were strangers.

The authors then played those isolated snippets of co-laughter to nearly 1,000 people from 24 cultures, from Americans to New Guinea highlanders. Subjects received no contextual information and with each example of co-laughter were asked, “Do you think these two people are friends or strangers?” In every culture, people accurately identified friend pairs. A second study, in which participants were asked, “how much do you think these people like each other,” showed similar results.

Interestingly, the results differed a little bit based on the laughers’ gender (all the pairs were either two men or two women): Participants were better at picking out sets of friends when those friends were female, and better at picking out strangers when they were male — possibly because, as the authors noted, female friends tend to laugh more in general than male or mix-gender friend pairs.

Either way, though, it’s a pretty impressive feat, considering that co-laughter between friends was no longer or otherwise obviously different than laughter between strangers. But when the researchers examined the sounds in greater detail, they found a few key differences: “Laugh features predicting listeners’ friend responses included shorter call duration, associated with judgments of friendliness and spontaneity, as well as greater pitch and loudness irregularities, associated with speaker arousal,” they wrote.

In other words: True laughter between friends was made up of more abrupt, varied sounds, while people who didn’t know each other tended to stick to more uniform ha-ha-has.There’s something a little heartwarming about this particular finding: There are so many situations where staying true to your authentic self can be a challenge, but here, at least, is one thing that’s tough to fake.

Laughter Between Friends Has Its Own Unique Sound