Self-awareness makes some yawn-susceptible.
Self-aware or empathetic people are more likely to catch the yawns, say US researchers1.
Contagious yawning is known to be more than coincidence. Studies have shown that 40-60% of people who watch videos or hear talk about yawning end up joining in. But psychologists have wondered what causes it. "It seems like such a hokey phenomenon," says psychologist Steven Platek at Drexel University in Philadelphia.
Platek and his colleagues at the State University of New York in Albany sat subjects in front of videos of others yawning and tallied their responses to find out why people are susceptible or immune to contracting yawns.
Those impervious to the infection also struggle to put themselves in other people's shoes, psychological tests showed. For example, they might be less likely to recognize that a social faux pas or insult could cause someone else offence.
Identifying with another's state of mind while they yawn may trigger an unconscious impersonation, the team suggests. The findings might also explain why schizophrenics, who have particular difficulty in doing this, rarely catch yawns.
This makes evolutionary sense, agrees Ronald Baenninger, who has studied yawning at Temple University in Philadelphia, Pennsylvania. Contagious yawning may have helped our ancestors to coordinate times of activity and rest. "It's important that all group members be ready to do the same thing at the same time," Baenninger says.
Yawning's underlying cause still remains obscure, however. One common perception - that it is triggered in an airless room by lack of oxygen - has been disproved. Experiments showed that people given more oxygen or carbon dioxide are just as likely to yawn.
Baenninger believes that yawning keeps the brain aroused in situations where sleep is unwanted. This would explain why our peak yawn times are in the early morning and when struggling to stay awake at night.
He has shown that stretching the mouth into a fake yawn tends to mimic the body's response to a real one, such as an increase in heart rate. But, "If you do a fake yawn, they likely or not turn into a real one," he says.
Platek, S. M., Critton, S. R., Myers, T. E. & Gallup, G. G. Jr. Contagious yawning: the role of self-awareness and mental state attribution. Cognitive Brain Research, 17, 223 - 227, (2003).
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Pearson, H. Kind people catch yawns. Nature (2003). https://doi.org/10.1038/news030728-2