Babies laugh just like monkeys, researchers report.
An analysis of recorded laughter from 44 infants, aged three to 18 months, revealed that the youngest babies laughed both as they inhaled and exhaled, just like nonhuman primates such as chimpanzees.
The older babies laughed mainly on the exhale, the same as older children and adults.
"Adult humans sometimes laugh on the inhale but the proportion is markedly different from that of infants' and chimps' laughs. Our results so far suggest that this is a gradual, rather than a sudden, shift," lead researcher Disa Sauter said in a Canadian Acoustical Association news release.
On the exhale
This shift doesn't seem to be linked to any particular developmental milestones.
The vocal control developed as people learn to speak may be why humans are the lone primates that laugh only when they exhale, Sauter said. She's a psychologist and associate professor at the University of Amsterdam in the Netherlands.
Researchers are now investigating if there's a link between the amount of laughter produced on the inhale and exhale and the reasons people laugh, which also change with age. In infants, laughter is tied to physical play like tickling. In older people, laughter is triggered by physical play as well as social interactions.
"Beyond that, I'd be interested in seeing whether our findings apply to other vocalisations than laughter," Sauter said.
This research could lead to new insight about vocal production in children with developmental disorders.
"If we know what normally developing babies sound like, it could be interesting to study infants at risk to see whether there are very early signs of atypical development in their nonverbal vocalisations of emotion," Sauter explained.
The study is scheduled for presentation at a Canadian Acoustical Association meeting in Victoria, British Columbia. Research presented at meetings is typically considered preliminary until published in a peer-reviewed journal.
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