Paratroopers yawn before jumping from planes. Violinists make it a practice before stepping on stage. Olympic contenders are known to do it just before their big event.
So says Prof. Robert R. Provine, who teaches psychology at the University of Maryland-Baltimore County and has studied yawning for 10 years. A neuroscientist intrigued by how the nervous system develops, he's learned lots about that relaxing gulp of air.
"Anxious people tend to yawn a lot," said Provine, who has studied the yawns of more than 1,000 people. "No one has shown it increases alertness, but that remains a possibility." And, he said, "Yawning may enhance performance."
Still, why we yawn remains a mystery. Provine is among the relatively few scientists in this country making yawning the focus of serious inquiry.
Yawning has been neglected as a field of research because it's so commonplace, Provine said in a recent interview in his campus lab.
"This behavior had been recognized as one that all people share, but it has been overlooked, because we do it every day," he said.
But research like Provine's, which documented how easy it is to get people to yawn just by showing them pictures of open mouths, may help unravel how the brain recognizes and uses visual information, he said.
This much is known, Provine said:
* The average yawn lasts about six seconds. We have little conscious control over the action, and stifling a yawn can't squelch the urge.
* We yawn the most in the hour after waking up. The second most common time yawns occur is the hour before sleep.
* We yawn when tired, anxious or bored.
* Yawning often is a byproduct of stretching; yawning itself might be a facial stretch.
The widely held belief that yawning is an automatic response to a shortage of oxygen or to the need to expel excess carbon dioxide has been discounted by Provine's experiments. He had 18 people alternately inhale carbon dioxide, oxygen, and room air, but found no corresponding change in yawning with any of those gases.
Seeing someone else yawn triggers yawning, a well-known phenomenon Provine backed up in the laboratory. It seems that just thinking about yawning can prompt that familiar twinge at the back of the throat.
"You see someone yawn, and you want to yawn," Provine said. "It's an unlearned class of social behavior with very deep and broad roots in human evolution."
In a series of experiments in 1989, Provine had 360 college students look at single videotape frames of various facial movements, including yawning and gaping mouths.
When viewing open mouths--regardless of whether the pictures were right side up, sideways or upside down--with few exceptions, the participants yawned in response.
It wasn't only the sight of a gaping mouth that triggered yawning. When shown a yawning face with the mouth cut from the picture, study participants felt as much urge to yawn as when the photo was intact.
Dr. Mary A. Carskadon, a professor of psychiatry and human behavior at Brown University, has conducted similar tests. Those who dismiss yawning as a foolish focus of research fail to appreciate its potential, she said. "When you see how (yawns) figure in brain maturation and communication, it gives a different context to this behavior."
Understanding why we yawn could have practical applications, from medicine to computers, Provine said.
Understanding the purpose of yawning could help doctors diagnose diseases, he said--or even aid scientists in developing computers that recognize the yawn of their users.