A US study that tracked eye movements of autistic and non-autistic toddlers watching animations found that autistic toddlers tended to pay more attention to those movements that coincided with sound rather than any other, giving a possible explanation for why autistic young children stare more at people’s lips (where motion and sound are synchronized: lip-synch) than any other other parts of the body that might be sending important social cues, such as the eyes.

The study, which was partly funded by the National Institute of Health’s National Institute of Mental Health (NIMH) was led by Dr Ami Klin, of the Yale Child Study Center at Yale University School of Medicine, New Haven, Connecticut, and colleagues, and was published online on 29 March in Nature.

Klin told the press that:

“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,” said Klin, explaining that, “toddlers with autism are missing rich social information imparted by these cues, and this is likely to adversely affect the course of their development.”

NIMH Director Dr Thomas R Insel, said:

“For the first time, this study has pinpointed what grabs the attention of toddlers with ASDs.”

“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 added.

We already know that autistic people don’t respond straight away to social cues, but it has not been clear what contributes to that during early childhood development, and what is absorbing their atttention instead.

The key discovery came when researchers watched children’s responses to sound and vision while watching a nursery rhyme cartoon.

For the study, Klin and colleagues tracked the eye movements of 76 two year olds with and without ASD while they watched cartoon animations on split screen displays.

Using a video game development technique called motion capture, the researchers reduced the movement of the cartoon characters to points of light so that only joints of the body were visible, like characters depicted by constellations of stars moving in the night sky.

The point of light animated characters moved normally, upright and forward on one half of the screen and upside down and backwards on the other half. The normal soundtrack accompanied both presentations: the characters spoke the same things at the same time, except in the lower screen the speech was accompanied by upside down and backwards movements of the body.

Previous studies have shown that upside down and backward presentations of such movements trigger different brain circuits and interferes with how young children perceive biological motion.

Eye movement tracks revealed that 21 toddlers with ASD showed no preference for either of the animations, whereas 39 typically developing toddlers clearly preferred to watch the upright and forward ones, as did 16 non-autistic but developmentally delayed toddlers.

But, there was a puzzling exception: when sound and movement synchronized more accurately in the upright and forward version, the ASD toddlers paid more attention to it. This happened in a pat-a-cake cartoon when the points of light of the character clapping his hands repeatedly synchronized with the loud clapping sound in the upright and forward screen but because of the upside down and backward orientation in the lower screen, the points of light did not synchronize as well with the clapping sound.

In the case of the pat-a-cake cartoon, the toddlers with ASD paid attention to the upright and forward version 66 per cent of the time, clearly showing a strong preference for this version.

The researchers began to suspect that what at first appeared to be random viewing of the other presentations could be that the toddlers with ASD were actually observing other sound and vision synchronicities that might not be so obvious to a more casual observer. So they went back and re-analyzed the earlier data and found this to be the case: the eye tracks of the ASD youngsters were showing a preference for following subtle synchronous changes in motion and sound.

They found that 90 per cent of the ASD toddlers’ eye tracks showed they preferred to follow audio-visual synchronies, whereas the typically developing children preferred to follow the most socially relevant movements.

Klin and colleagues then followed up with tests using new animations that optimized audiovisual synchrony and confirmed the results.

The researchers suggested that these findings might explain something they discovered in an earlier study: that ASD children as young as 2 show a preference for watching people’s mouths rather than their eyes. It could be because the mouth is the feature with the most synchrony between sound and motion: lip-synch.

Klin said their findings 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,” added Klin.

“Two-year-olds with autism orient to non-social contingencies rather than biological motion.”

Ami Klin, David J. Lin, Phillip Gorrindo, Gordon Ramsay & Warren Jones.

Nature advance online publication 29 March 2009.

doi:10.1038/nature07868

Sources: NIH/National Institute of Mental Health.

Written by: Catharine Paddock, PhD