If someone near you yawns, do you yawn, too? About half of adults yawn after someone else does in a phenomenon called contagious yawning. Now a new study has found that most children aren't susceptible to contagious yawning until they're about 4 years old -- and that children with autism are less likely to yawn contagiously than others.

The study, conducted by researchers at the University of Connecticut, appears in the September/October 2010 issue of the journal Child Development.

To determine the extent to which children at various stages of social development are likely to yawn contagiously, the researchers studied 120 typically developing 1- to 6-year-olds. Although babies begin to yawn spontaneously even before they leave the womb, most of the children in this study didn't show signs of contagious yawning until they were 4.

The team also studied about 30 6- to 15-year-olds with autism spectrum disorders (ASD), comparing them to two other groups of typically developing children with the same mental and chronological ages. The children with ASD were less likely to yawn contagiously than their typically developing peers, the researchers found. And children with diagnoses that imply more severe autistic symptoms were much less likely to yawn contagiously than those with milder diagnoses.

"Given that contagious yawning may be a sign of empathy, this study suggests that empathy -- and the mimicry that may underlie it -- develops slowly over the first few years of life, and that children with ASD may miss subtle cues that tie them emotionally to others," according to the researchers. This study may provide guidance for approaches to working with children with ASD so that they focus more on such cues.