The secret to strong social skills? Genuine laughter from five months old

Infants as young as five months old can differentiate the sound of laughter between friends and the laughter between strangers, a new study from researchers at New York University (NYU) and the University of California Los Angeles  (UCLA) has found.

The results are of interest to those in the early childhood education and care (ECEC) sector as they suggest that the ability to detect the nature of social relationships is instilled early in life, with implications for children’s social and emotional growth based on the interactions of adults around them, including ECEC educators. The results suggest that the ability to detect the nature of social relationships is instilled early in human infancy, possibly the result of a detection system that uses vocal cues.

The vocal cues between educators in the ECEC environment, the study suggests, are important foundational aspects to help children scaffold their learning about genuine and reciprocal relationships, friendship, and emotional interaction.

“Infants’ sensitivity to different kinds of laughter might be one of the early emerging tools they use to understand and navigate the complex social world,” study co-author Dr Athena Vouloumanos said.

“Instances – even very brief instances – of shared laughter can reveal rich information about people’s relationships, detectable in infants as young as five months of age and universally by adults around the world,” added co-author Dr Gregory Bryant.

Recent studies into ‘co-laughter’ – simultaneous laughter between two or more individuals – have shown that adult listeners across different cultures and languages can quickly evaluate the nature of relationships between people: are they friends, acquaintances, or strangers based on the intonation and changes in the laughter pattern.

Doctors Vouloumanos and Bryant used their research to determine if this ability is evident in infants, with the aim of revealing how early in life information in vocalisations can be used to detect the type of relationships we see involving third parties.

In the study, researchers examined how five-month-olds processed the exchanges of co-laughter of adults – specifically, those who were strangers and those who were friends – by gauging how long they listened to these sounds.

In the first of two experiments, five-month-old infants heard alternating audio recordings of colaughter between friends and between strangers; here, the infants listened longer to colaughter between friends. These results showed, then, that infants could not only differentiate between the two types of laughter, but, when given the choice, they preferred to listen to friends laughing.

In a second experiment, the researchers linked visual depictions of friends and strangers to their colaughter in order to determine if the infants could tie colaughter to judgments about human relationships.

Infants saw two types of video clips of actors interacting: in one, two women faced and smiled at each other, as if they were friends; in another, the two women turned their backs to each other, indicating that they were strangers. Both videos froze on a still frame of the actors facing the infant with neutral expressions. Infants then heard alternating audio recordings of friends’ laughter or strangers’ laughter.

The researchers predicted that if infants recognised the social context that was appropriate to each type of laughter, they would look longer when the laughter and social context were mismatched — that is, when stranger co-laughter followed interactions between friends or when friend co-laughter followed those between strangers.

Gaze length is also a commonly used measurement for spotting infants’ comprehension of interactions, with a longer gaze evidence of surprise — or, in this case, a mismatch between co-laughter and the nature of the relationship.

As predicted, the infants looked longer when the social interaction was incongruent with the type of co-laughter, suggesting that they could match the colaughter that fit the depicted social relationships.

“The ability to rapidly evaluate acoustic features in co-laughter that reveal social relationships between individuals appears early in human infancy and might be the product of an adaptive affiliation detection system that uses vocal cues,” the authors concluded.

The study, Five-month-old infants detect affiliation in colaughter, has been published in Scientific Reports.