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April 6, 2009
Toddlers With Autism Preoccupied By Audiovisual Synchrony
One of the hallmarks of autism spectrum disorders (ASD) is an unusual pattern of eye contact during social interactions, particularly a tendency to look toward people's mouths rather than their eyes. A new finding may explain why.
Children pay special attention to what researchers call "biological motion," such as human movement, from within days of birth. By 3 months, infants already prefer to look more at a person's eyes than other parts of the face. But toddlers with ASD don't pay special attention to human movement.
Researchers believe these toddlers are missing the rich social information imparted by biological motion, which is likely affecting the course of their development. Supporting this idea, the brain regions involved in biological motion perception overlap with those involved in perceiving basic social signals such as facial expressions.
A team led by Dr. Ami Klin and Dr. Warren Jones of the Yale Child Study Center wanted to understand what children with ASD were paying attention to. Funded by NIH's National Institute of Mental Health (NIMH), Autism Speaks and the Simons Foundation, they tracked the eye movements of 2-year-olds with and without ASD while the toddlers looked at cartoon animations on split-screen displays. The cartoons played normally on one half of the screen, but upside-down and in reverse on the other half. The normal soundtrack of the actor's voice, recorded when the animations were made, accompanied the presentations.
As reported online in Nature on March 29, 2009, the eye-tracking data showed that 39 typically developing toddlers and 16 developmentally delayed but non-autistic toddlers clearly preferred the upright animations. In contrast, 21 toddlers with ASD had no preference, looking back and forth between the 2 animations. However, their responses to 1 animation didn't fit this pattern.
The toddlers with ASD shifted their attention to the upright figure 66% of the time—a strong preference—during a game of pat-a-cake, where the figure claps his hands repeatedly. The researchers realized that what made the pat-a-cake animation unique was that the movement of the animated figure seemed to cause the clapping sound. The synchrony of action and sound only existed on the upright side of the screen; the inverted figure was played in reverse and so its motions weren't in sync with the soundtrack.
This clue led the researchers to suspect that the toddlers with ASD might have a preference for audiovisual synchrony. That would explain why children with ASD look more at peoples' mouths than their eyes as early as age 2. The mouth is the facial feature with the most audiovisual synchrony, with lip motion matching the sounds of speech.
Re-analyzing the data to factor in changes in motion and sound, the researchers found that audio-visual synchronies accounted for about 90% of the preferred viewing patterns of toddlers with ASD. A follow-up experiment using new animations optimized for audiovisual synchrony confirmed the finding.
"For the first time, this study has pinpointed what grabs the attention of toddlers with ASDs," said NIMH Director Dr. Thomas R. Insel. "In addition to potential uses in screening for early diagnosis, this line of research holds promise for development of new therapies based on redirecting visual attention in children with these disorders."