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Contact: Morgan Kelly
Princeton University

Chewing/lip Smacking

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Caption: Two recent studies based at Princeton University suggest that the oral-facial component of human speech evolved from lip smacking, a friendly back-and-forth gesture performed by primates. The studies show that the mechanics of primate lip smacking are distinct from those of chewing, similar to the separate mechanics of human speech and chewing. X-ray movies of adult rhesus macaques showed that lip smacking (left) results in a fast, loosely coordinated movement of internal structures such as the lips (green dot), tongue (red dot) and hyoid (blue dot) -- just as in human speech. Also similar to humans, chewing (right) produced a slow, tightly coordinated movement of these components in macaques. These parallels suggest that in primates chewing and lip smacking -- as with chewing and speech-related facial movement in humans -- have separate neural controls. With further study, the neural pathway in primates from the brain to facial mechanics could help illuminate the neurological basis of speech disorders in humans.

Credit: Videos courtesy of Asif Ghazanfar

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Related news release: Out of the mouths of primates, facial mechanics of human speech may have evolved

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