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Baby faces show the right side of emotion.

Baby faces show the right side of emotion

The crease of a smile and the angle of a frown are providing surprising clues to how the brain generates spontaneous emotional expressions in the first year of life.

In two independent studies, researchers document greater emotional intensity on the right side of the face among infants, although previous investigations indicate emotional expressions are more intense on the left side of the face among right-handed adults.

Researchers assume the adult pattern reflects the influence of the brain's right hemisphere, which controls many muscles on the left side of the face and is crucial in generating emotional displays. In addition, the left hemisphere -- which controls much of the right side of the face -- may be more important in inhibiting emotional displays, thus contributing to more intense expressions on the left side.

The new evidence suggests the right hemisphere matures more quickly during infancy, says psychologist Catherine T. Best of Wesleyan University in Middle-town, Conn. Its initial specialization for emotion apparently involves dampening the expression of spontaneous emotions produced deep within the brain. As the left hemisphere matures and emotions come under more voluntary control during preschool years, its inhibiting effect on emotions eventually may surpass that of the right hemisphere.

Best and colleague Heidi F. Queen made computer copies of photographs of six smiling and four crying babies between 7 and 13 months of age. Each half of a face was then combined with its mirror image. For example, the right side of a smiling face was flopped over to create a complete face. In a series of experiments reported in the March DEVELOPMENTAL PSYCHOLOGY, right-handed university students used a seven-point scale to rate the intensity of emotional expression in each composite image. They also determined whether the right- or left-side composite for each infant was more expressive.

Right-sided expressions were rated as more intense, the researchers note, especially when the mouth was rated separately. Crying expressions were rated as more intense than smiling expressions.

Another study, conducted by Mary K. Rothbart and her co-workers at the University of Oregon in Eugene, had undergraduates rate the intensity of distressed and happy expressions made by 59 infants videotaped several times between 3 and 13 1/2 months of age. Using stills from the videotapes, raters covered each half of a baby's face before making a judgment.

Again, expressions were significantly more intense on the right side of the face, say the psychologists, who will describe their findings in an upcoming NEURO-PSYCHOLOGIA.

Best says these results support evidence of an earlier right-hemisphere inhibition of spontaneous left-sided movements in general. For instance, most infants prefer to turn their heads and bodies to the right (SN: 1/7/89, p.10).

"While we can only speculate now on the brain development that mediates the change from infant to adult facial [patterns]," Rothbart says, "a better understanding of this process may not only explain facial expressions -- it may also clarify basic mechanisms of emotional development."
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Title Annotation:research on how brain generates emotional expression
Author:Bower, Bruce
Publication:Science News
Date:Mar 11, 1989
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