Only about 11 percent of children with an autism spectrum disorder yawned after the storyteller yawned, compared to 43 percent of typically developing children.
Among children with autistic disorder, a more severe form of the syndrome, none yawned contagiously, while about 23 percent of kids with pervasive developmental disorder -- a milder form of autism -- yawned.
"Typical infants seem to be growing more emotionally attuned with others as they age, with the age of 4 being critical for that," Helt said. "Kids with autism don't seem to be becoming more and more emotionally attuned with others as they age."
The study doesn't prove that a lack of "contagious yawning" is a sure sign of a developmental problem.
Helt also noted that it's possible that the autistic children weren't paying attention to others around them, or they noticed the yawns and other facial expressions but didn't know how to interpret them.
Geraldine Dawson is chief science officer for Autism Speaks, an advocacy group dedicated to funding research into the causes, prevention, treatment and a cure for autism. She said: "It is well known that children with autism are less likely to imitate other people. This study suggests that this difficulty in imitation extends to very basic behaviors, such as yawning."
Intervention programs that target "imitation skills" can be very effective in helping children with autism in their social development, she added.
In a second study in the same issue of the journal, researchers from the Institute of Education in London found that thinking and perception skills of children with autism spectrum disorders can vary substantially among individual children and can improve over time.
The researchers assessed the abilities of 37 children with autism spectrum d
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