Babies posture to learn.

A 9-month-old infant placed on a wooden platform spies a brightly colored ball and crawls awkwardly but relentlessly toward the toy. He reaches the platform's edge and vainly thrusts an arm in the air. The ball lies beyond his reach on another platform, across a sheer drop of more than 2 feet. Unperturbed, he keeps right on going, as if to crawl through thin air.

Never fear, an attending adult plucks the reckless baby from harm's way. Yet the child's not always so rash. The same infant stays put if the adult seats him with his legs dangling over the platform's edge. There, the baby sits with ease and gazes at the tempting toy. Given a second chance to crawl, however, the infant will again take the plunge.

Consider this a lesson in the surprisingly close affinity of learning to early postural milestones--sitting, crawling, and walking. As they master each posture, infants must learn new ways to control their bodies and to factor depth information into their actions, contends psychologist Karen E. Adolph of New York University. Thus, babies make better action-oriented decisions when they're in a familiar posture, she says.

Adolph and her coworkers studied 11 boys and 8 girls, all 9 months old. Each child had nearly 4 months of experience at sitting upright but had been crawling for only about 1 1/2 months. While sitting, the babies usually avoided reaching across a gap for a toy that was too far away to grasp, Adolph reports in the July PSYCHOLOGICAL SCIENCE. In contrast, when in a crawling pose, the same kids frequently headed off the platform toward a distant toy and had to be scooped up by the experimenter.

In related work, Adolph found that babies who learn to avoid steep slopes as crawlers have to educate themselves about inclines all over again as novice walkers (SN: 3/20/99, p. 184).

Demonstrations of posture-specific learning provide a challenge to influential theories about why babies refuse to crawl off experimental setups where a sheet of safety glass creates the illusion of a sheer drop to the floor far below. Those theories suggest that regardless of expertise at crawling or other postures, infants stop at a visual cliff's edge only after having taken enough actual falls to become scared of heights or after figuring out that empty space can't support a body.