Flexibility in intercepting moving objects.

When hitting moving targets, the hand does not always move to the point of interception in the same manner as it would if the target were not moving. This could be because the point at which the target will be intercepted is initially misjudged, or even not judged at all, but it could also be because a different path is optimal for intercepting a moving target. Here we examine the extent to which performance is degraded if people have to follow a different path than their preferred one. Forcing people to make small adjustments to their path by placing obstacles near the path hardly influenced their performance. When the orientation of elongated targets was manipulated, people adjusted their paths, but not quite enough to avoid intercepting the targets at a sub-optimal angle, probably because following a more curved path would have reduced the spatial accuracy and taken more time. When the task was to hit targets in certain directions, people had to sometimes follow much more curved paths. This gave rise to larger errors and longer movement times. An asymmetry in performance between hitting moving targets further in the direction in which they were moving and hitting them back from where they came is consistent with the different consequences of timing errors for the two directions of target motion. We conclude that the path that people take to intercept moving targets depends on the precise constraints under the prevailing conditions rather than being a consequence of judgment errors or of limitations in the way in which movements can be controlled.