Children as young as 5 months can perform rudimentary addition and subtraction, indicating that humans are born with an inherent mathematical ability well before they are taught arithmetic, an Arizona researcher has found.
The results, to be reported today in the British journal Nature, appear to resolve a long-running debate on whether children distinguish among small numbers of items by consciously counting or by purely perceptual, non-numerical means.
The new research shows that they do count, said psychologist Karen Wynn of the University of Arizona, the paper's author.
"Infants are not just passive recipients that take in the world passively, but they can actively make inferences and reason about some aspects of the world," she said. "This is another instance of infants having a more surprising understanding of the world than we had known."
The findings provide "apparently cast-iron evidence . . . that young babies' intellectual skills may go a good deal further" than scientists had previously expected, said psychologist Peter E. Bryant of Oxford University. The paper "is a notable event in the history of developmental psychology," he added.
During the past 20 years, researchers have found that infants display a remarkable variety of intuitive skills. Well before they are six months old, infants can tell objects apart by their size, shape and color. They can tell when objects are solid or not. They know that objects continue to exist when they are hidden. They can even tell if a speaking person's lip movements are appropriate for the speech they are hearing.
"These are striking skills to find in a creature which used to be thought of as utterly incompetent and ineffective, but they could all in one way or another be described -- even dismissed -- as perceptual," Mr. Bryant said.
Researchers have long argued whether infants can directly recognize differences in the number of items or simply see that one group is larger or smaller than another. Ms. Wynn's results, he said, indicate that the infants have a real numerical skill.
Ms. Wynn used a "looking-time" procedure that is widely employed in studying infants. In essence, the technique relies on the fact that infants will stare longer at something that is surprising or unexpected than they will at something that is predicted.