Abused kids face up to angry expressions. (Hostile Intent).

Physical abuse at home does more than leave some children with broken bones, burns, and other injuries. Scientists now suspect that, over time, this parental cruelty tunes a school-age child's perceptual system to pick up signs of anger in others' facial expressions.

Physically abused kids adapt to their harsh reality by developing an emotional radar for glimmers of anger, theorizes psychologist Seth D. Pollak of the University of Wisconsin-Madison.

"Perceptual categories for specific emotions are flexible and subject to learning during childhood," Pollak says. As an abused child's brain incorporates this emphasis on detecting anger, he or she has increasing difficulty connecting with others in school and elsewhere, Pollack suggests.

He and Wisconsin colleague Doris J. Kistler report their findings in the June 25 Proceedings of the National Academy of Sciences.

Using posed facial expressions of happiness, sadness, fear, and anger, the researchers created digital images that gradually change from one emotion to another. For example, in one series of images, a face starts angry and ends up sad, displaying a shifting blend of the emotions in between.

Pollak and Kistler presented these images to 23 physically abused and 17 nonabused children, all around 9 years old. The children first examined pairs of faces with slightly different expressions and tried to identify which of the pair matched a third face. A given facial pair might include, say, one face that is 100 percent happy and one that's 80 percent happy and 20 percent sad. The children then reported what they saw as the dominant emotion in each image.

Both abused and nonabused kids recognized pure expressions of each emotion. The two groups also responded comparably to blends of happiness with sadness or fear.

However, abused children reacted far more strongly than the others did to signs of anger. They labeled faces as angry even when that emotion contributed only 40 percent to the expression. Nonabused children identified anger only when it contributed at least 70 percent. Moreover, abused kids had more difficulty than their nonabused peers did in telling apart expressions that predominantly consisted of anger.

These findings highlight how children learn to cope with physical abuse, comments psychologist Megan R. Gunnar of the University of Minnesota in Minneapolis--St. Paul. "Physically abused kids become experts at perceiving anger with a minimal amount of information," she says.

A parallel process may apply to children of depressed parents, adds psychologist Nathan A. Fox of the University of Maryland at College Park. These kids could become sensitized to elements of sadness in facial expressions.