By Megan Marples, CNN
Laughter transcends all languages ââ- and now scientists know that this spontaneous response is also universal in some species of primates.
The laughter of human infants matches that of great apes, according to a study published Tuesday in Biology Letters.
Human adults laugh mainly on exhaling, while infants and great apes laugh during inhaling and exhaling, said study author Mariska Kret, associate professor of cognitive psychology at Leiden University in the United States. Netherlands.
First, adults inhale, then produce “ha-ha-ha” sounds in short bursts, starting loud and then fading, Kret said.
“The monkey type is harder to describe but there is an eh-ha-huh-ha alternation,” she added.
Infant laughter is not necessarily similar to that of all great ape species, but only those that are evolutionarily closest to humans, such as chimpanzees and bonobos, said. Marina Davila-Ross, a lecturer in comparative psychology at the University of Portsmouth in England, who was not involved in the study.
âIt seems to reflect that laughter is to some extent deeply rooted biologically,â she said.
Kret originally discovered this phenomenon while attending a talk by famous primatologist Jan van Hooff with a friend. When van Hooff said the monkeys laughed during inhale and exhale, Kret’s friend showed a video of her baby laughing in the same way.
To test whether infants laughed like monkeys, Kret collected audio clips of humans aged 3 months to 18 months laughing and asked listeners to rate the percentage of laughter produced by inspiration versus the expiration.
As a control, the researchers also included five clips of adults laughing.
After two rounds with at least 100 listeners each, the results were known. People could tell that infants laughed both when breathing in and breathing out, while adults mostly laughed when breathing out.
To ensure the results were accurate, Kret commissioned expert listeners to analyze the sound clips and their conclusions aligned with those of the novices.
Exhaling laughter is more contagious
The researchers also rated the listeners on the most pleasant and contagious sounds.
The results showed that the more laughter was produced on exhaling, the more people perceived it as positive.
The researchers confirmed this finding when they conducted another experiment and asked a new group of listeners to rate how positively they perceived laughter without being told about breathing patterns. The new group also found the dying laughter more enjoyable.
The laughter produced by the exhale tends to be louder and more controlled, Kret noted, which she says makes it easier for infants to communicate that they are having fun and want to keep playing.
Older infants produced more exhaling laughter
The older infants in the study also produced more exhaling laughter than the younger ones.
This could be because as babies grow older they learn “the function of communication and parents see that the baby is actively trying to clarify something,” Kret said.
Davila-Ross said she was surprised to see that the airflow associated with laughter changes as infants grow older.
“It would actually be very interesting to see if such changes can also be found for other non-verbal vocalizations of humans,” she added.
In future research, Kret said she hopes to repeat her experience with other vocalizations such as crying.
She is currently conducting other laughter experiments, including one involving orangutans, gorillas, and humans to see if they alter the sound of their laughter to mimic the laughter of those around them.
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