Bimanual coordination in children: manipulation of object distance.

The performance of many everyday activities requires the coordination of the two upper limbs to achieve the goal of the task. Although bimanual performance has been studied in detail in adults, few studies have examined how children coordinate the movements of the two hands during symmetric and asymmetric bimanual prehension. With the current study, we asked younger (4-6 years, n = 14) and older (7-10 years, n = 16) children to complete a discrete bimanual task. Specifically, they reached to grasp cylinders located at near and far positions in either unimanual or bimanual condition. During bimanual symmetric conditions, participants performed movements with both hands toward two objects located at the same distance (both near or both far), while in the bimanual asymmetric conditions, they reached for objects at different distances. Results of the kinematic analyses indicated that the young children consistently experienced the "two target" effect, whereby bimanual movements were executed more slowly than unimanual movements to the same distance. Older children employed a hybrid strategy, exhibiting slower movements in bimanual congruent conditions, but larger non-dominant apertures in bimanual incongruent conditions. This hybrid strategy was hypothesized to stem from developmental changes occurring in the integration of sensory information around 8 years of age. While older children exhibited temporal and spatial coordination patterns that were similar to patterns reported in adults, large relative timing differences at the start and end of bimanual movements and considerably weaker spatial coupling were seen in the younger children.