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Gabriel Diaz, Flip Phillips, Brett Fajen; Intercepting moving targets: A little foresight helps a lot. Journal of Vision 2008;8(6):622. doi: 10.1167/8.6.622.
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Behavioral studies suggest that humans performing a fixed-heading interception task regulate velocity to maintain a constant bearing angle (CBA); that is, to null the change in the target's exocentric direction. This purely feedback-driven CBA strategy has been contrasted with a purely predictive strategy that requires the pursuer to predict the eventual time and location of the future interception point. However, there exists a continuum of possible strategies in between the purely feedback-driven CBA strategy and the purely predictive strategy that have yet to be considered. Our study is aimed at investigating these intermediate strategies in which the pursuer regulates velocity to null the change in bearing angle a short time into the future. Subjects sat in front of a large projection screen and watched computer generated displays that simulated linear self-motion over a textured ground plane. Simulated speed was controlled by adjusting a foot pedal, the position of which was mapped onto speed according to a first-order lag. A spherical target approached the subject's path from one of two angles, at one of two initial speeds, and along one of five potential trajectories with varying degrees of curvature. Human performance was compared with a model of interception behavior that, at each time-step t, produced the velocity adjustment that would minimize the change in bearing angle at time t+Δt, taking into account the target's behavior during that interval. By adjusting the parameter Δt, the model can simulate the full range of strategies between the purely feedback-driven CBA strategy (Δt = 0) and the purely predictive strategy (Δt = target's time-to-contact with the interception point). We found that the model most closely approximates the human data when Δt is at intermediate values, suggesting that subjects regulate velocity to null the change in bearing angle a short time into the future.
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