Did you hear the one about the monkey that walked into a bar?
A new study has shown that young babies laugh both as they inhale and exhale, similar to nonhuman primates, such as chimpanzees. All great ape species laugh, but according to the study, human laughter differs from that of other primates. Humans laugh primarily on the exhale, whereas other primates laugh on both the inhale and exhale.
The study looked at whether human infants laugh in a similar manner to apes. This was not something that was pulled out of thin air, however - babies and primates have both been found to laugh when tickled or during play, whereas human adults have been found to primarily laugh during many different kinds of social interactions.
To test the hypothesis that the proportion of infants' laughter produced on the exhale increases with age, researchers examined whether human infant laughter is acoustically more similar to non-human apes' laughter. They studied clips of laughter from 44 infants aged 3 to 18 months, which confirmed that at younger ages, human infants' laughter is similar to that of other great apes. They also discovered that older babies laughed mainly on the exhale, similar to older children and adults.
"Adult humans sometimes laugh on the inhale but the proportion is markedly different from that of infants' and chimps' laughs," said lead researcher Disa Sauter, psychologist and associate professor at the University of Amsterdam in the Netherlands. "Our results so far suggest that this is a gradual, rather than a sudden shift."
Experts claim that this shift isn't linked to any particular developmental milestones. As we learn to speak, said Sauter, the vocal control we develop may be linked to why humans are the only primates that laugh when they exhale. Researchers also plan to investigate whether or not there is a link between the amount of laughter produced on the inhale and exhale and the reasons people laugh. These reasons also change with age.
Despite how it may seem, this study wasn't just for giggles. Researchers hope that by studying how babies laugh, it 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 said.