Intercepting moving targets: a little foresight helps a lot.

Behavioral studies suggest that humans intercept moving targets by maintaining a constant bearing angle (CBA). The purely feedback-driven CBA strategy has been contrasted with the strategy of predicting the eventual time and location of the future interception point. This study considers an intermediate anticipatory strategy of moving so as to produce a CBA a short duration into the future. Subjects controlled their speed of self-motion along a linear path through a simulated environment to intercept a moving target. When targets changed speed midway through the trial in Experiment 1, subjects abandoned an ineffective CBA strategy in favor of a strategy of anticipating the most likely change in target speed. In Experiment 2, targets followed paths of varying curvature. Behavior was inconsistent with both the CBA and the purely predictive strategy. To investigate the intermediate anticipatory strategy, human performance was compared with a model of interceptive behavior that, at each time-step t, produced the velocity adjustment that would minimize the change in bearing angle at time t + Deltat, taking into account the target's behavior during that interval. Values of Deltat at which the model best fit the human data for practiced subjects varied between 0.5 and 3.5 s, suggesting that actors adopt an anticipatory strategy to keep the bearing angle constant a short time into the future.