There’s nothing worse, when you’re trying to stay awake at work during the postlunch lull, than looking over and seeing a colleague yawn. To most of us, yawning seems all too contagious, but a new study in the journal Child Development suggests that the ability to “catch” a yawn actually requires some sophisticated social skills.

Psychologists at the University of Connecticut studied more than 120 children, who ranged in age from one to six. While reading each child a story, a researcher would stop several times to yawn conspicuously. Fewer than 10 percent of the children younger than four yawned in response. Among the older kids, that percentage jumped significantly, with 35 to 40 percent of kids displaying contagious yawning.

“We know that the social brain develops over the first few years of life,” says Molly Helt, the study’s lead author and a doctoral student in psychology. Although youngsters are certainly sensitive to others’ expressions, she says, their brains may not yet be capable of unconsciously mirroring those emotions. “At some point we sort of start to take on the emotions of other people without even thinking about it,” Helt says.

In the second part of the study the researchers put kids with autism through the same scenario. They discovered that children with disorders on the autism spectrum were significantly less likely to catch yawns—among five- to 12-year-olds, 11 percent yawned, compared with 43 percent of typically developing children.

Although kids with autism may have no problem identifying that someone else is yawning, Helt says, their brains seem less likely to respond by unconsciously mimicking the expression back. “They’re not developing that automatic emotional linkage with those around them,” Helt says. “If we learn more about how the social brain wires up in the early years, maybe we can take that and apply it to kids with autism as an early intervention.”