Why humans are good with tools but chimps are not

New York: Ever wondered why we can use tools with such dexterity while nonhuman primates such as capuchin monkeys and chimpanzees can not?

Humans use what's known as a vision for action system. Visual information is integrated into planning action and guiding movements of the body in space, especially to use the hands to reach for and grasp objects and manipulate them in space, the researchers said.

Between 16-18 months and two years, humans develop a new relationship between vision and action.

Human children aged two, three and four and adult nonhuman primates were tasked to fit a stick, a cross and a tomahawk into a matching cut-out space on a tray.

Two-year-olds were able to fit the straight stick and the cross-shaped stick properly into the cut-out most of the time. Three- and four-year-olds were even better at it.

However, when it came time to fit the tomahawk stick into the cut-out, two-year-olds were unable to complete the task most of the time, while three and four-year-olds were also challenged.

Children were adept at using sight to help figure out how an object should be aligned to fit it into the space.

Sometimes some of the three and four-year-olds would hold the object, especially the cross or tomahawk stick, a little bit above the tray and move it in the air as if they were aligning it visually before they put it down.

Instead of depending on sight, nonhuman primates often used their sense of touch, known as their haptic senses, to feel how the object fit into the space.

"Adult chimps and capuchin monkeys are among the most accomplished spatial problem solvers among the nonhuman primates, but even the two-year-olds are much better than they are at alignment," said lead researcher Dorothy Fragaszy from University of Georgia.

When asked to complete the task in a two-dimensional version, children were less successful.

"You can feel when a three-dimensional object hits the edge of a cut-out. You do not feel anything with a flat two-dimensional object such as a disk. For nonhuman primates, the haptic component is essential," Fragaszy said.