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An NIH-funded study in 2-year-olds with autism spectrum disorders (ASD) suggests why they might find mouths so attractive. It is the lip-sync — the exact match of lip motion and speech sound.
ASD children were preoccupied with this audiovisual synchrony. Unaffected peers focused on socially meaningful movements instead — gestures and facial expressions.
The research was led by Ami Klin, PhD, of the Yale Child Study Center, and was funded in part by NIH’s National Institute of Mental Health.
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. Toddlers with autism are missing rich social information imparted by these cues, and this is likely to adversely affact the course of their development.
Klin, along with Warren Jones, PhD, and colleagues at Yale, reported the findings online in the journal Nature.
This study, for the first time, has pinpointed what grabs the attention of toddlers with ASD, says NIMH Director Thomas R Insel, MD.
“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,” he adds.
The researchers had a eureka moment when they noticed children’s responses to audiovisual synchrony that was embedded in a nursery rhyme cartoon.
While it was known that people with autism don’t spontaneously orient to social signals, it was unclear what early-emerging mechanism contributes to that.
So Klin, Jones and colleagues 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 video games, 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. They played 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 presentation. Initially, eye-tracking data 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, the 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, unlike the others, 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. 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.
So the researchers began 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.
Audio-visual synchronies accounted for about 90 percent of the preferred viewing patterns of toddlers with ASD and none of unaffected toddlers. Typically developing children focused instead on the most socially relevant information.
And a follow-up experiment, using new animations optimized for audiovisual synchrony, confirmed these results.
Klin, Jones and colleagues also recently reported that children with autism look more at people’s mouths than eyes as early as age 2. Since the mouth is the facial feature with most audiovisual synchrony — lip motion with speech sound — the researchers propose that their new findings offer a likely explanation for this phenomenon.
Our results suggest that, in autism, genetic predispositions are exacerbated by atypical experience from a very early age, altering brain development. Attention to biological motion is a fundamental mechanism of social engagement, and in the future, we need to understand how this process is derailed in autism, starting still earlier, in the first weeks and months of life.
NIMH is funding Klin and Jones’s related research project that explores related behaviors in infants who have older siblings already diagnosed with ASD, and who, because of the genetic heritability risk in autism, have greater risk of also developing the condition.
Source: press release from http://www.eurekalert.org on 3/30/09. The name of the report published inNature is “Two-year-olds with autism fail to orient toward human biological motion but attend instead to non-social physical contingencies. Klin A, Lin DJ, Gorrindo P, Ramsay G, Jones W. Nature, 2009 Mar 29.
Also participating in the research were David Lin, now at Harvard Medical School; Phillip Gorrindo, now at Vanderbilt University; Gordon Ramsey, PhD, Haskins laboratories. The study was funded through the NIH’s STAART Program (Studies To Advance Autism Research & Treament).
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