Why is it that when we see someone yawn, it’s often so hard not to do the same? Is yawning contagious? This was the question investigated in a new study from researchers from Tohoku University in Japan, who found it’s perceptual sensitivity rather than the common explanation of empathy that’s responsible for the hard-to-stop yawning.  

The study involved showing subjects photos of people yawning in order to get them to yawn. Hidden cameras observed the participants, while a machine tracked their eyes. The subjects were given 60 photos with four levels of yawning, differing in intensity. The people had to judge whether the depicted person was yawning. To have a control comparison, they were also shown 60 happy and 60 angry photos and asked to remark if the people were angry or happy. 

Those who were more likely to detect yawning were also those who were more likely to start yawning. Sensitivity to angry or happy faces did not seem to relate to contagious yawning in a meaningful way.

To see if yawning is related to empathy, the participants were measured for their Autistic Quotient (AQ) via an autism-spectrum questionnaire. This also showed little relation to yawning frequency. Interestingly, female subjects had a higher susceptibility to being caught by the yawning contagion. 

Dr. Chia-huei Tseng, the lead researcher on the study and an associate professor at Tohoku University, explained that recent clinical observations showed how individuals with autism or schizophrenia did not yawn like typical people. This led some to link the lack of empathy to being unaffected by contagious yawning and prompted their investigation.

"We find that for non-clinical population, perceptual ability is more closely related to contagious yawning than empathy is," said Tseng. "Since it's been documented that people with autism tend to suffer from impaired perception such as an atypical eye gazing on faces and a difficulty in judging facial emotions, it's possible that their perceptual limitation causes them to be unable to detect someone else's yawning expression. This is a possible explanation for their lack of contagious yawning."

What causes yawning is still largely a mystery, with psychologist Andrew Gallup proposing it may be needed to cool the brain. A 2016 study from the State University of New York did find an notable link between yawning and the size of one’s brain. Brain size may be linked to yawn length. Creatures with smaller brains, like gorillas and elephants, yawn for a shorter time than humans.

You can check out the new study right here.