CHICAGO - Within days of their birth, healthy babies will look you in the eye. By 4 months, they will delight in others. And by 9 months, they will exchange smiles.

Jacob Day did none of those things.

"We used to say it was like it burned his eyes to look at you," said his mother, Tamie Day, of Antelope, Calif. "It wasn't just that he wasn't looking at us; he was purposefully looking away."

Day, who has a psychology degree, suspected her son might have autism. She enrolled him in a study, published in April, that found that babies such as Jacob are indeed at high risk for autism if they do not respond to their names by the age of 1.

At 18 months, Jacob was diagnosed with autism, about a year earlier than usual. Before he turned 2, he began daily intensive behavior treatment to help him lead a more normal life.

Doctors and scientists are increasingly looking for early signs in babies of autism, attention deficit disorder, and other mental problems that, just a generation ago, scarcely anyone thought could appear in children so young.

Some scientists even believe that intensive treatment in some babies can actually prevent autism, attention deficit disorder and other problems.

An Institute of Medicine report in 2000 helped energize the idea. The report emphasized the plasticity of babies' brains. It also explained how interacting with babies can change their brain wiring.

"We used to say 'nature vs. nurture,' but now people really think it's 'nature through nurture,' " said the University of Chicago's Lawrence Gray.

Babies typically begin making eye contact soon after birth, and "understand at a basic, perhaps hard-wired, level that eyes are special - they look more at eyes than at other parts of the face," said Sally Ozonoff, an autism specialist at the University of California-Davis MIND Institute.

When his mother expressed her autism concerns at Jacob's six-month checkup, the doctor said "we were being a little overzealous," Day said.

Still, there was no pointing, no clapping, no shared smiles, and, when Jacob would laugh, it seemed like his own private joke. So his parents sought out UC-Davis specialists, who gave them the diagnosis.

Jacob, now 31/2, has made meaningful progress thanks to treatment, his mother said, including a breakthrough moment at age 2, when he looked up and gazed into her eyes. "He was smiling up at me and I realized that was the first time he had done that," she said.

Interest in infant mental health has been boosted by awareness of the prevalence of attention deficit disorders and autism, which government officials said in February affected 1 in 150 U.S. children and may be more common than previously thought.

In April, researchers from the federal Centers for Disease Control and Prevention and the Interdisciplinary Council on Developmental and Learning Disorders presented a report emphasizing earlier diagnosis and treatment.

The report said that about 17 percent of U.S. children have a developmental disability such as autism, mental retardation, and attention deficit-hyperactivity disorder, but that fewer than half were diagnosed before starting school.