Why youngsters try to do impossible things

When you see a small child try to fit into or on top of a doll-sized toy, you’re likely to laugh. That’s what three developmental psychologists initially did when their own toddlers attempted to fit into a toy car, a miniature room and a doll’s crib.

Judy DeLoache, the Kenan Professor of Psychology at U.Va., and co-investigators from Northwestern University and the University of Illinois at Urbana-Champaign set out to understand why youngsters, who actually know better, could ever make such dramatic mistakes about scale.

Not to worry, moms and dads. The study of 18- to 30-month-old children, published in the journal Science, found these kinds of errors — scale errors — to be common in this age group. Videotapes show many participants in the research seriously trying to slide down miniature slides, squeeze into tiny toy cars and sit in dollhouse chairs at U.Va.’s Child Study Center.

The children’s dramatic failures to use size when interacting with familiar objects may reflect immaturity in the interaction of two brain systems — one involved with the visual recognition of objects, the other with perception of object size, said DeLoache, who was lead author of the study. “In scale errors, the usual seamless integration between the two systems in the brain momentarily breaks down, and the size of an object is not incorporated into a child’s decision to act on it. However, once the action begins, children do use size information to adjust their motor behavior,” she said.

In deciding to get into the miniature car, children ignore how small it is, but then they accurately open its tiny door and aim a foot directly at its impossibly small opening. “There’s a dissociation between the use of size for planning actions versus controlling those actions,” said DeLoache.

“Even infants can discriminate the size of objects, so the question is why children sometimes ignore the fact that the objects are so small,” said David Uttal of Northwestern.

The answer to that question fits with theories that implicate two neurally and functionally distinct brain systems underlying the use of visual information. One brain area is involved in visually recognizing and categorizing objects (“That’s a chair.”) and planning what to do with them (“I’m going to sit down.”). Another is involved in perception of object size and use of visual information to control actions on objects.

“One reason this is so interesting is that similar kinds of dissociations occur in various neurological impairments in adults, but they have rarely been studied in healthy young children,” said Karl S. Rosengren of the University of Illinois at Urbana-Champaign.

The study also suggests a failure of inhibitory control, implicating immaturity of the prefrontal cortex.

The youngsters were put in a playroom with three large objects, then exposed to miniatures identical except for size. They were observed interacting with an indoor slide they could walk up and slide down, a child-sized chair they could sit in and a car they could get inside and, with their feet, propel around the room. The children were then taken for a walk, and when they returned to the room, they found the miniatures. If they did not spontaneously interact with the replacements, experimenters drew their attention to them without commenting on their size. From videotapes, the investigators identified 40 scale errors by 25 of the 54 children studied.