Motion prediction and the velocity effect in children

In coincidence-timing studies, children have been shown to respond too early to slower stimuli and too late to faster stimuli. To examine this velocity effect, children aged 6, 7.5, 9, 10.5, and adults were tested with two different velocities in a prediction-motion task which consisted of judging, after the occlusion of the final part of its path, the moment of arrival of a moving stimulus towards a specified position. A similar velocity effect, resulting in later responses for the faster velocities than for the slower, was found primarily in the three younger groups of children (for the longer occlusion conditions: 600-1,320 milliseconds). However, this effect was not seen in all children in these groups. Individual analyses showed that this velocity effect, when present, is linked to the use of distance rather than time information, or to the confusion between these in extrapolating the occluded trajectories. The tendency to use one type of information or the other is a good predictor of accuracy and variability in this task and a good indicator of the development stage of the participants. Across development, children tend to initially use distance information with poor accuracy but relative consistency in responses. In a second stage, they use time and distance information alternatively across trials trying to find a better source of information with still poor accuracy and now great variability. In a final stage, they use time information to reach consistency and accuracy in their responses. This chronology follows the stages proposed by Savelesbergh and Van der Kamp (2000) explaining development with an initial stage of 'freezing' non-optimal relationships between information and movement, then a 'freeing' stage during which new solutions are searched for, and finally an 'exploiting' stage with an optimal relationship between information and movement.