Reaching movements in children: accuracy and reaction time development.
The present study was undertaken to follow the development of the capability to produce adult-like fast and precise movements reaching visual targets, during childhood. A two-dimensional reaching task was used. We focussed on pre-planning capabilities, by instructing subjects to produce movements as fast as possible, preventing corrections after initiation of movement. The capability of information processing and accurate motor response production were assessed by measuring reaction time (RT, the time elapsed between target presentation and movement onset), movement time (MT, the time elapsed between movement onset and movement end) and precision of response (correlation of response extent and direction with target distance and direction). One child (male) was tested repeatedly since age 6 until age 9. At age 7, RTs decreased. At age 8, accuracy increased, after a temporary decrease at 7. Both accuracy and RT eventually reached the adult level. MTs were similar to the adult ones right from the beginning and they never changed significantly. The results were confirmed in four groups of five children each, aged 6, 7, 8 and 9, respectively. A control group of five adults was also tested. It is concluded that, between age 6 and 9, children become capable of quickly processing visual target information and producing accurate fast and uncorrected reaching trajectories based upon proprioceptive information only, like those typical of adults, by shortening RTs and improving precision, while maintaining adult-like MTs throughout. The capability of quickly reacting to a target acting as a ;Go' signal (measured by RT) and that of information processing to program an accurate motor trajectory (measured by the precision achieved) appear not to be developmentally linked, the former improving earlier, the latter later.