Study of a Servo-control Strategy for Projectile Interception

Models of a servo control strategy for projectile interception proposed by Chapman (1968) are developed in order to determine how the strategy performs in the presence of important constraints known to limit the performance of human fielders. Simulation experiments were conducted for two cases: (a) The fielder is initially in the plane of projectile motion and moves forwards and backwards in this plane—the 1D case. (b) The fielder is not initially in the plane of projectile motion—the 2D case. Simulations showed that Chapman's strategy is robust and works well in the 1D case despite various limiting constraints. Model behaviour was qualitatively similar to published data on human performance. In the 2D case the strategy works to some extent, but performance is severely limited. Including an additional control action as originally suggested by Chapman can improve matters considerably. The problem of how to distinguish use of Chapman's strategy from an alternative predictive strategy is raised. Despite considerable problems in making such a distinction, simulation studies indicated a possible observable difference. This was tested in a simple experiment: The results tended to favour Chapman's strategy but did not enable a predictive strategy to be definitively ruled out.