According to a new research, watching how a tot reacts to cartoons could help spot autism.
It is already known that individuals with autism spectrum disorders (ASD) tend to stare at people's mouths rather than their eyes. Now, the new study of 2-year-olds with the social deficit disorder has suggested why they might find mouths so attractive: lip-sync-the exact match of lip motion and speech sound.
"Typically developing children pay special attention to human movement from very early in life, within days of being born. But in children with autism, even as old as two years, we saw no evidence of this," explained Ami Klin, Ph.D., of the Yale Child Study Center, who led the research.
"Toddlers with autism are missing rich social information imparted by these cues, and this is likely to adversely affect the course of their development," the expert added.
The research's crucial moment came when researchers followed up on a clue from children's responses to audiovisual synchrony embedded in a nursery rhyme cartoon.
While it was known that people with autism do not spontaneously orient to social signals, it was unclear what early-emerging mechanism may contribute to that. Nor was it clear exactly what they were attending to instead. To find out, the research team tracked the eye movements of two-year-olds with and without the disorder while they looked at cartoon animations on split-screen displays.
The researchers borrowed a technique from the video game industry, called motion capture. They then reduced the movements to only points of light at each joint in the body, like animated constellations. These cartoons played normally, upright and forward, on one half of the screen, but upside-down and in reverse on the other half. The inverted presentation engages different brain circuits and is known to disrupt perception of biological motion in young children.
The normal soundtrack of the actor's voice, recorded when the animations were made, accompanied the presentations.
Eye-tracking data initially showed that 21 toddlers with ASD had no preference for the upright animations, looking back and forth between the two. By contrast, 39 typically-developing toddlers and 16 developmentally delayed but non-autistic toddlers clearly preferred the upright animations.
However, responses to one animation didn't fit the pattern. The toddlers with ASD changed their behavior and shifted their attention to the upright figure as it played a game of pat-a-cake, where the figure claps his hands repeatedly.
In this animation, the movements of the points of light actually cause the clapping sound. This physical synchrony-dots colliding to produce a clapping sound-only existed on the upright side of the screen, because the inverted figure played in reverse and its motions weren't in sync with the soundtrack.
The children with ASD chose the upright figure 66 percent of the time, a strong preference.
This clue led the researchers to suspect that what initially appeared to be random viewing by the ASD toddlers might actually reflect preference for audiovisual synchronies that were less obvious than the clapping. So they re-analyzed the data, factoring in more subtle synchronous changes in motion and sound.
A follow-up experiment using new animations optimized for audiovisual synchrony confirmed these results.
The study has been published in the journal Nature.