SAN DIEGO, May 4 (UPI) -- U.S. researchers say infants who have older siblings with autism often fail to seek emotional cues from adults as other toddlers would.

Psychology professor Leslie Carver of the University of California, San Diego, says the study, presented at the 2007 International Meeting for Autism Research in Seattle, is the first to investigate "social referencing" behavior in children from families at high risk for autism.

"Our results," Carver said in a release, "support two important ideas about autism: That those behaviors that are diagnostic of the disorder fall on one end of a broad behavioral spectrum, and also that there is a strong genetic component to autism, evidenced by the behavioral resemblance in close family members."

Social referencing involves checking in with the emotional displays of others and regulating our own emotions and behavior in response. While most children begin social referencing at about age of 1, this behavior is impaired in individuals with autism.