Planning manipulative hand movements: Do young children show the end-state comfort effect?

Adults plan ahead in order to avoid extreme joint angles because meeting a task's precision requirements is easier when joints are in a comfortable position. This effect is known as the end-state comfort effect and the precision hypothesis explains it. The name precision hypothesis is used because it addresses a state that allows movements to be performed with greater precision. The present study examined whether young children plan motor actions on the basis of the end-state comfort effect and whether an increasing demand for precision would make the effect more apparent. Forty children (age range=2.7-5.9 years) performed a task of picking up a bar with one hand and inserting one of its distal parts into a hole flush with the top of a box. Two bars differing in their distal shapes were used to manipulate precision: a cylindrical (Low Precision) and a semi-cylindrical (High Precision) bar. Children of all ages did not show the end-state comfort effect, even when the task demanded high precision for its conclusion. Instead, a start-state comfort was common with the right overhand being the preferred grip. This might indicate that (a)planning is restricted for grasping the bar; (b)the use of a preferred hand (right) in a given posture (overhand) may be a strong constraint on the selection of the grip pattern.