Ignoring ‘Biological Motion’ Could Be an Early Warning Sign for Autism

by Carl Sherman

June 17, 2009

Children aren’t usually diagnosed with autism until they are 3 or older because the disorder’s hallmark social deficits often aren’t apparent until then. But research at the Yale Child Study Center suggests that the absence of a fundamental capacity underlying socialization could lead to an earlier diagnosis—and a head start on treatment.

Within days of birth, human infants (and other species’ young) are drawn to movements made by living things. Earlier research found this preference for “biological motion” missing in autistic adults, adolescents and school-age children. A study published March 29 in Nature by Ami Klin, director of the Yale autism program, Warren Jones and colleagues showed the same thing in children as young as 2 with autism. What attracted these children instead was audiovisual synchrony—patterns of movement matched by sounds.

The study tracked eye movements of 21 toddlers diagnosed with autism, 39 typically developing children and 16 who were developmentally delayed but not autistic. They watched five point-light animations of human figures—cartoons reduced to moving points of light at the joints—playing children’s games such as “peek-a-boo” and “pat-a-cake” accompanied by a soundtrack. The animations were displayed on a split screen next to the same figures turned upside down and run backward, which disguises biological motion.

The nonautistic children paid significantly more attention to the upright figure, while the eyes of the children with autism moved apparently at random between the figures.

There was one exception: Watching the “pat-a-cake” animation, children with autism, too, looked more at the upright figure than the reversed, inverted version. The reason, the researchers conjectured, was synchrony—only in the clapping game were sound and movement clearly coordinated.

To test their hypothesis, the researchers reanalyzed the autistic toddlers’ seemingly random response to the other sequences. “We found that underlying their visual behavior was a strong pursuit of audiovisual synchrony,” Klin says. “It accounted for 90 percent of the variation.”

The attraction to synchrony could explain an earlier observation by the same researchers: While typically developing 2-year-olds watch the eyes of adults who are speaking to them, children with autism look at adults’ mouths, where movement matches sound most closely. “Autistic children can learn what words mean this way, but intention is expressed in the eyes, not the mouth,” Klin says. “They can’t learn about things that are conveyed intuitively, rather than explicitly.”

More broadly, the failure of a mechanism that draws attention to human movement could lay the groundwork for more complex failures of social development. “You would think that if this perceptual bias were knocked out, other abilities that might build on it would be corrupted,” says Charles Nelson, research director of the developmental medicine center at Children’s Hospital, Boston, who was not involved in this research.

Klin doesn’t think inattention to biological motion causes autism. “It’s one of the earliest, most robust reflections of social disability, but not the only one,” he says. “It’s a proxy for something even more fundamental, which probably will be described in a neurochemical or molecular way.”

At the same time, the absence of a behavioral response that is normally evident in the first week of life might enable doctors to detect signs of autism, and start treatment, long before more obvious symptoms become apparent, he says.

 Nelson agrees: “I can imagine its use as a screening tool. If we see an abnormal response in a high-risk child, these are the kids we’d pay attention to.”

Understanding what attracts the attention of children with autism might also help researchers design more effective interventions. “Perhaps we can manipulate the environment to minimize distraction and increase reward from things more conducive to social development,” Klin says.