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This is Scientific American — 60-Second Science. I'm Christopher Intagliata.A baby's laugh is unmistakable: (CLIP: baby laughter) But aside from its squealing, high-pitched quality, there's another factor that sets a baby's laugh apart from ours: babies laugh on the exhale AND the inhale. Whereas adult humans "tend to laugh predominantly on the exhale. The classic kind of ha-ha-ha." Disa Sauter, a psychologist who studies emotions at the University of Amsterdam. Sauter and her colleagues collected 44 samples of babies laughing, from the ages of 3 months... (CLIP: 3 months) to 10 months... (CLIP: 10 months) all the way up to 18 months. (CLIP: 18 months)They played the samples for about 100 untrained volunteers, and asked them to deconstruct the laughs. Were the babies laughing on the inhale, the exhale, or both? "And there we find a nice relationship between the age of the baby and the amount of the laughter happening on the inhale." The younger the baby, the more laughs on the inhale. Because remember, our laughs gravitate towards the exhale as we age. And Sauter thinks one reason for that could be that we gain more vocal control as we learn to talk: because speaking also happens primarily on the exhale.  She presented the preliminary findings at a meeting of the Acoustical Society of America, in Victoria, Canada. The researchers are in the process of checking the judgments of the volunteers against those of professional phoneticians. As it happens: human babies aren't the only primates who laugh both breathing out and breathing in . (CLIP: chimp) Chimps do it too."They go like hoo hoo hoo. You know, they laugh more continuously while inhaling and exhaling. But it's... yeah, true, it's totally difficult to do on purpose." But Sauter, I thought, pulled off a pretty good impression. "I'll take that as a compliment! (laughs)"
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