The laughing patterns of human infants match those of another species, a new study finds

Megan Marples 2021
Researchers (Biology Letters) found that infants laugh in a similar pattern to great apes.

Laughter transcends all languages --
now Mariska Kret (Leiden Univ NL) cs know this spontaneous response is universal across some primate spp, too:
The laughing patterns of human infants match those of gr.apes:
-human adults primarily laugh while exhaling,
-infants & gr.apes laugh during inhalation & exhalation.
First adults inhale, then produce "ha-ha-ha" sounds in short bursts, starting loud, then fading away:
"The ape-type is more difficult to describe,
but there is an alternation huh-ha-huh-ha."

Marina Davila-Ross (Univ.Portsmouth , not involved):
Infant laughter isn't necessarily similar to all gr.ape spp, just chimps & bonobos:
"It seems to reflect that laughter is to some extent biologically deeply grounded."

Kret originally discovered this phenomenon while attending a talk by Jan van Hooff.
When van Hooff said apes laugh during inhalation & exhalation, Kret's friend showed a video of her baby laughing in the same manner.
Kret collected audio clips of humans ages 3 to 18 months old laughing,
she asked listeners to rate what % of the laugh was produced by inhaling vs exhaling.

As a control, researchers also included 5 clips of adults laughing.
After 2 rounds incl.>100 listeners each, the results were in:
-infants laughed both while in- & exhaling,
-adults mainly laughed by exhaling.

To ensure the results were accurate, Kret had expert listeners analyze the sound bites,
their findings aligned with those of the novices.
Exhaling laughter is more contagious
Researchers also had the listeners rate, which sounds were the most pleasant & contagious.
The results showed:
the more that the laughter was produced by exhaling, the more people perceived it as positive.
Researchers confirmed this finding when they conducted another experiment:
they asked a new group of listeners to rate how positively they perceived the laughter without being informed of breathing patterns.
The new group also found exhaling laughter to be more pleasant.
Kret:
Laughter produced by exhaling tends to be louder & more controlled,
this makes it easier for infants to communicate that they are having fun, and want to continue playing.

Older infants in the study also produced more exhaling laughter than younger ones.
Kret:
This could be because, as babies grow up, they learn "the communicative function of it, and parents see that the baby is actively trying to make something clear."

Davila-Ross was surprised to see that the air-flow ass.x the laughter changes as the infants grew older:
"Can such changes also be found for other non-verbal vocalizations of humans?"

In future research, Kret hopes to repeat her experiment with other vocalizations, e.g. crying.
Kret is currently running other laughter experiments, incl. one involving orangs, gorillas & humans:
do they change the sound of their laughter to mimic the laughter of those around them?

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