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How long infants spend looking at other people's eyes may be an early marker of autism, a new study suggests.

In the study, infants watched a video of a person acting like a caregiver, while the researchers tracked their eye movements.

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Infants that later developed autism were found to show declines in how long they looked at the caregiver's eyes, starting around ages 2 months to 6 months.

By age 2, children with autism looked at caregiver's eyes about half as long as children without autism.

The earlier doctors can identify autism, the more effective treatments are thought to be. Future studies may help researchers figure out how to preserve some of the eye-looking skills that babies with autism seem to have at birth, the researchers said.

Future treatment may be able to "build on that early eye-looking and help reduce some of the associated disabilities that often accompany autism," said study researcher Warren Jones, of Emory University.

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