Abstract
When humans observe the actions of others, they can often accurately anticipate the outcome of those actions. This is perhaps best exemplified on the playing field, where athletes must anticipate the outcome of an action based in part on the complex movement of an opponent's body. In this study, we tested the reliability and use of local and distributed sources of information available in the actor's motion. These issues were investigated within the context of blocking a penalty kick in soccer. Because of extreme time constraints, the keeper must anticipate the direction in which the ball is kicked before the ball is contacted, forcing him or her to rely on the kicker's movement. In Experiment 1, we used a motion capture system to record the joint locations of experienced soccer players taking penalty kicks. The reliability of both local (e.g. orientation of the non-kicking foot) and distributed (e.g. mode/motor synergy) sources of information was measured by computing the degree to which each source correlated with true kick direction. Experiment 2 investigated the relationship between reliability and use of information sources. The motion data were used to create animations from a keeper's viewpoint of a point-light kicker approaching and kicking a ball. On each trial, subjects watched an animation and judged kick direction (left or right). The sources of information upon which judgments were based were identified by computing the correlation between information and judged kick direction. By comparing the reliability and use of different sources of information, we can characterize the ability to exploit local and distributed information when anticipating a movement's outcome. In Experiment 3, we presented subjects with artificial stimuli in which only one source of information was reliable, providing a more direct test of people's ability to use specific sources of information.