Word of the Day: Pandiculation
Keep track of the number of times you yawn while reading this:
Myth states that we yawn to get rid of extra carbon dioxide and take in more oxygen. In 1987, Provine* et al tested this idea on - who else - college students. They were given different gas mixtures to breath, one of which contained 100x the level of CO2 in normal air. Although respiratory rate increased, there were no differences in the number or duration of yawns between the normal air and the gas mixtures groups.
Every vertebrate species yawns but apparently it's only contagious in humans. As the good Dr. Seuss put it in his Sleep Book "A yawn is quite catching you see. Like a cough. It just takes one yawn to start other yawns off."
It's still unclear why yawns are contagious, but Provine has tested what triggers the yawning. When test subjects just see a yawning mouth, it doesn't trigger a yawn. But if the mouth is covered and the nose and eyes of the yawning face shows, it does.
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Have you yawned yet? :)
* Robert R. Provine is Professor of Psychology and Assistant Director of the Neuroscience Program at the University of Maryland Baltimore County.