Toddlers ride rail to tool use. (Behavior).

At 16 months of age, many children adapt the way they use a handrail as they walk across a perilously narrow bridge to reach their parents on the other side. These on-the-fly changes that keep them from falling represent an early example of tool use, a hallmark of human intelligence, conclude two psychologists in the May Developmental Psychology.

Sarah E. Berger of Adelphi University in Garden City, N.Y., and Karen E. Adolph of New York University studied 24 boys and 24 girls. Most had been walking for about 4 months. Each 16-month-old had a series of chances to walk from one platform to another across a 29-inch-long wooden board that was either narrow (5 or 7 inches across) or wide (from 14 to 28 inches across). On half the trials, a handrail was placed on one side of the bridge. An experimenter followed alongside children to ensure their safety.

Toddlers always tried to walk across wide bridges, rarely touching the handrail when it was available. Most reached their destination on their own.

In contrast, toddlers often stayed off narrow bridges that lacked a handrail but usually attempted to cross those that had one. A majority of such crossings were successful, especially if kids first touched and explored the handrail and then grabbed it on the way across while slowing their pace and taking smaller steps. Kids also did better on narrow bridges if they switched their method of holding the handrail during a crossing, such as going from a one-handed grip facing frontward to a two-handed grip facing sideways. These adaptations show that the toddlers were using the handrail as a tool to help them achieve a goal that they could not otherwise attain, say the researchers.--B.B.