The use of online control: a developmental perspective.

ABSTRACT

To date very little research has addressed the abilities of young participants to respond to a change in visual information provided during movement execution. This study attempted to determine the ability of 45 participants (5, 7, 9 years) to respond to a change in visual information during a discrete rapid aiming movement. A perturbation paradigm where the target size changed after movement onset was used. In the control context, movements were made to each target size (small, medium, large) with no perturbation. In contrast, during the experimental context the target always began as a medium target. Upon movement initiation, the target size could remain constant or might unexpectedly become larger or smaller. Temporal, kinematic, and correction data were collected to determine the control process underlying the aiming movement. No interaction was found between age and condition for movement time (MT), and results indicated that all ages scaled movement time to final target size. The accuracy data revealed the 9-year-old participants were more accurate than the 5- and 7-year-old participants. To determine where the changes in duration were made, the time to and after peak velocity (TTPV, TAPV), and peak velocity values (PV) were examined. The PV values indicated that, during the control context, the participants scaled their movement to the target size. However, during the experimental condition generally no significant differences were found in either measure, suggesting a programmed response based on the original target size. This was supported by the correction data collected prior to peak velocity, lending further support to a programmed response. Following peak velocity, it was found that differences in MT were as a result of time spent in deceleration. This increased TAPV, and increased number of corrections observed, suggest that all participants were using on-line control following peak velocity in response to the change in visual information. The data collected supports a model of control that incorporates both open-loop control during the initial impulse phase, and closed-loop control during the current control phase for participants as young as 5 years.