Washington: Contagious yawning may not be linked to empathy and tiredness and could decrease as one ages, a new study has found.
The study from the Duke Centre for Human Genome Variation could ultimately shed light on illnesses such as schizophrenia or autism.
"The lack of association in our study between contagious yawning and empathy suggests that contagious yawning is not simply a product of one's capacity for empathy," said study author Elizabeth Cirulli.
Contagious yawning is a well-documented phenomenon that occurs only in humans and chimpanzees in response to hearing, seeing or thinking about yawning, researchers said.
It differs from spontaneous yawning, which occurs when someone is bored or tired.
Previous research, including neuro-imaging studies, has shown a relationship between contagious yawning and empathy, or the ability to recognise or understand another's emotions.
Other studies have shown correlations between contagious yawning and intelligence or time of day.
Interestingly, people with autism or schizophrenia, both of which involve impaired social skills, demonstrate less contagious yawning despite still yawning spontaneously.
A deeper understanding of contagious yawning could lead to insights on these diseases and the general biological functioning of humans, researchers said.
The researchers recruited 328 healthy volunteers, who completed cognitive testing, a demographic survey, and a comprehensive questionnaire that included measures of empathy, energy levels and sleepiness.
The participants then watched a three-minute video of people yawning, and recorded the number of times they yawned while watching the video.
The researchers found that certain individuals were less susceptible to contagious yawns than others, with participants yawning between zero and 15 times during the video.
Of the 328 people studied, 222 contagiously yawned at least once. When verified across multiple testing sessions, the number of yawns was consistent, demonstrating that contagious yawning is a very stable trait.
The only independent factor that significantly influenced contagious yawning was age: as age increased, participants were less likely to yawn.
However, age was only able to explain 8 percent of the variability in the contagious yawn response.
"Age was the most important predictor of contagious yawning, and even age was not that important. The vast majority of variation in the contagious yawning response was just not explained," Cirulli said.
The study was published in the journal PLOS ONE.