Children with autism often have difficulty making eye contact, and now a new study suggests this may be due in part to how their brains process visual information, rather than being purely a social deficit.
In the study, children with autism showed activity over a larger area of the brain's cortex when an image was placed in the periphery of their visual field, compared with when the image was placed in the center of their visual field. The opposite was true in children who did not have the disorder.
When a child with autism avoids eye contact, "we are very much inclined to interpret this as a social deficit," said study researcher John Foxe, a neuroscientist at Albert Einstein College of Medicine in New York. "But it may be a much more fundamental issue," stemming from a reduced ability early in life to control the muscles that govern eye movements, he said.
In the study, the researchers looked at 22 children with autism, and 31 kids without the disorder. A checkerboard pattern was flashed in front of the children on a screen, while electrodes were used to measure their brain activity. The researchers tried to determine how much of the cortex's area was dedicated to processing the checkerboard's location.
For most people, a much larger area of the cortex is dedicated to the center of the visual field, as opposed to the periphery. "If you put your thumb up, out in front of you at an arm's length, it takes up about 1 degree of visual space, and your brain has about 4 square centimeters of cortex devoted to it. If you move your thumb six or eight inches to right, now only 1.5 square millimeters of cortex is devoted," Foxe explained.
In the study, "what we found was that indeed, at peripheral locations, children with autism spectrum disorders showed larger responses in the cortex," he said.
The "map" of the cortex, in which the space allotted to each visual field is set, develops early in life. The new finding suggests that "children with autism have a basic difference in how their visual cortex is mapped," Foxe said. "More neurons were being devoted to process information in the periphery."
It's known that children with autism often have deficits in their motor skills, and it may be that during infancy, this extends to a reduced ability to control eye movements, which prevents the cortex from being mapped as it is in people without the condition, Foxe said.
The inability to control eye movements certainly doesn't cause autism, but may work"like gasoline on a fire," Foxe said. An infant with autism may be unable to direct their eyes to exactly where they want, and people in the child's life react to not having eye contact with the child. People think the child is disengaged from social interactions, so they disengage, and it becomes a cycle, he said.
However, much more research is needed to confirm whether this is true, the new study provides only the first evidence of this idea, he said.
Further research should also test younger children, he said. The youngest children in the new study were 7, but autism can reliably be diagnosed as early as age 3 or 4, and may even be detected during the first months of a child's life, he said.