Children's development of reaching: temporal and spatial aspects of aimed whole-arm movements

Age-related changes in movement time and spatial distribution of pointing errors were investigated using a whole-arm target-aimed task. 60 children (6 to 11 yr.) and 10 young adults were required to reach towards targets located on a vertical screen in four conditions: target lit for 4 sec. in light (1), in darkness (2), target lit for 200 msec. in light (3), in darkness (4). Accuracy was perfect in Conditions 1 and 2, with a significant increase of MT in Condition 2 between the ages 7 and 10. Accuracy decreased slightly in Condition 3 and strongly in Condition 4, despite a similar shortening of MT. In Condition 4 the subjects undershot the target position: horizontally from age 8 and vertically in all age groups, with an increase of vertical bias by girls at age 9. These results suggest age-related changes in computation of arm movement towards the target.