Michael E. McCarty

Problem Solving in Infancy: The Emergence of an Action Plan

Young childrens strategies were evaluated as they grasped and used objects. Spoons containing food and toys mounted on handles were presented to 9-, 14-, and 19-month-old children with the handle alternately oriented to the left and right. The alternating orientations revealed strategies that the children used for grasping items. Younger children usually reached with their preferred hand, disregarding the items orientation. In the case of the spoon, this strategy produced awkward grasps that had to be corrected later. Older children anticipated the problem, alternated the hand used, and achieved an efficient radial grip (i.e., handle grasped with base of thumb toward food or toy end) for both orientations. A model of the development of action-selection strategies is proposed to illustrate planning in children younger than 2 years.

The Beginnings of Tool Use by Infants and Toddlers

Children (aged 9, 14, 19, and 24 months) were encouraged to use tools to achieve a demonstrated goal. Each tool was most efficiently applied when held by the handle with the thumb toward the head of the tool in a radial grip. The tools were presented at midline and oriented to the left and right on alternating trials, so the children who managed to grasp a tool in both orientations with the radial grip demonstrated planning of actions in advance. The tools included a spoon, hairbrush, toy hammer, and magnet; the goals were to feed ones self, feed another, brush ones hair, brush anothers hair, hit pegs, and retrieve metal objects. Children were found to use more radial grips with the self-directed tools (i.e., hairbrush-to-self and spoon-to-self), indicating that they could plan their actions better when directed toward the self than toward an external goal.

Evidence of Motor Planning in Infant Reaching Behavior

When adults reach for an object, kinematic measures of their approach movement are affected by what they intend to do after grasping it. We examined whether such future intended actions would be reflected in the approach-to-grasp phase of infant reaching. Twenty-one 10-month-old infants were encouraged to either throw a ball into a tub or fit it down a tube. Kinematic measures of the approach phase of the reach toward the ball were obtained using a motion analysis system. Infants, like adults, reached for the ball faster if they were going to subsequently throw it as opposed to using it in the precision action. The perceptual aspects of the ball were the same and cannot account for these kinematic differences. Infants appear to be planning both segments of their actions in advance. Our findings provide evidence for a level of sophistication in infant motor planning not reported before.

How Infants Use Vision for Grasping Objects

The role of vision was examined as infants prepared to grasp horizontally and vertically oriented rods. Hand orientation was measured prior to contact to determine if infants differentially oriented their hands relative to the objects orientation. Infants reached for rods under different lighting conditions. Three experiments are reported in which (1) sight of the hand was removed (N = 12), (2) sight of the object was removed near the end of the reach (N = 40, including 10 adults), and (3) sight of the object was removed prior to reach onset (N = 9). Infants differentially oriented their hand to a similar extent regardless of lighting condition and similar to control conditions in which they could see the rod and hand throughout the reach. In preparation for reaching, infants may use the current sight of the objects orientation, or the memory of it, to orient the hand for grasping; sight of the hand had no effect on hand orientation.

Self-directed action affects planning in tool-use tasks with toddlers

Toddlers grasp a tool more effectively when it is self-directed (e.g., spoon) than other-directed (e.g., hammer), possibly because the consequences of self-directed actions are more obvious. When the negative consequences of an inefficient grip were made equally salient, the self-directed versus other-directed differences remained.