Eye contact during early infancy may be a key to early identification of autism, according to a new study.
When and how long a baby looks at other people's eyes within the first two to six months offers the earliest signs of whether a child is likely to develop autism, scientists say.
The study reveals the earliest sign of developing autism ever observed - a steady decline in attention to others' eyes within the first two to six months of life.
Typically developing children begin to focus on human faces within the first few hours of life, and they learn to pick up social cues by paying special attention to other people's eyes, researchers said.
Children with autism, however, do not exhibit this sort of interest in eye-looking. In fact, a lack of eye contact is one of the diagnostic features of the disorder.
To find out how this deficit in eye-looking emerges in children with autism, Warren Jones and Ami Klin from the Marcus Autism Center, Children's Healthcare of Atlanta, and Emory University School of Medicine followed infants from birth to age 3.
The infants were divided into two groups, based on their risk for developing an autism spectrum disorder.
Jones and Klin used eye-tracking equipment to measure each child's eye movements as they watched video scenes of a caregiver.
The researchers calculated the percentage of time each child fixated on the care-giver's eyes, mouth, and body, as well as the non-human spaces in the images. Children were tested at 10 different times between 2 and 24 months of age.
By age 3, some of the children - nearly all from the high risk group - had received a clinical diagnosis of an autism spectrum disorder.
The researchers then reviewed the eye-tracking data to determine what factors differed between those children who received an autism diagnosis and those who did not.
"In infants later diagnosed with autism, we see a steady decline in how much they look at mom's eyes," said Jones.
This drop in eye-looking began between two and six months and continued throughout the course of the study.
By 24 months, the children later diagnosed with autism focused on the care-giver's eyes only about half as long as did their typically developing counterparts.
"Autism isn't usually diagnosed until after age 2, when delays in a child's social behaviour and language skills become apparent. This study shows that children exhibit clear signs of autism at a much younger age," said Thomas R Insel, director of National Institute of Mental Health (NIMH).
The study was published in the journal Nature.