How do babies laugh? Like chimpanzees!

Few things can delight an adult more easily than the brazen and uninhibited laugh of a baby. A new study shows, however, that babies' laughter differs from adult laughter in a decisive way: babies laugh while breathing out and inhaling, in a remarkably similar way to non-human primates.

The research will be described by Disa Sauter, psychologist and associate professor at the University of Amsterdam in the Netherlands, during a lecture given at the 176th meeting of the Acoustical Society of America, on the sidelines of Acoustics Week in Canada 2018 from the Acoustical Society of America, November 5-9 at the Victoria Conference Center in Victoria, Canada.

Together with colleagues, psychologist Mariska Kret and graduate student Dianne Venneker of the University of Leiden in the Netherlands, and Bronwen Evans, PhD student at University College London-Sauter, studied sequences of laughter taken in 44 infants and children aged 3 to 18 months. The recordings were taken from online videos in which babies were engaged in playful interactions. The recordings were then analyzed by 102 listeners, recruited from a population of psychology students, who evaluated how much laughter in each clip was produced at the expiration compared to inhalation.

Sauter and her colleagues discovered that younger babies usually laughed both by inspiration and by exhalation, like nonhuman primates like chimpanzees. In older babies studied, however, laughter was mainly produced on exhalation, as is the case in older children and adults.

"Adult humans sometimes laugh while inhaling, but the proportion is markedly different from that of laughing infants and chimpanzees.Our results suggest that this change is gradual rather than sudden," said Sauter, who points out that the transition does not seem be linked to particular stages of development. She noted, however, that these results were based on the judgments of non-expert auditors. "We are currently checking these results against the judgments of the phoneticians, who annotate in detail the bursts of laughter."

Sauter said that there was no reason allowed for humans, alone among primates, to laugh only by exhalation. One possibility, she said, is that it results from the vocal control that humans develop when they learn to speak.

Researchers are currently examining whether there is a link between the amount of laughter produced during inspiration and the expiration and the reasons individuals laugh, which also change with age. In infants and younger babies, as in nonhuman primates, laughter is the result of a physical game like tickling. In the elderly, laughter can come from a physical game but also from a social interaction.

"Beyond that, I would like to know if our findings apply to other vocalizations than laughter," Sauter said. Ultimately, the research could offer insights into the vocal production of children with developmental disabilities. "If we know what developing babies look like, it might be interesting to study infants at risk in order to see if there are any very early signs of atypical development in their nonverbal vocalizations." emotion."

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More information:
Presentation # 3aSC5, "How do babies laugh?" by Disa Sauter, Bronwen Evans, Dianne Venneker and Mariska Kret will be on Wednesday, November 7th at 9:25 am in SALON A at the Victoria Conference Center in Victoria, British Columbia, Canada. acousticalsociety.org/asa-meetings/