Toward a unified fielder theory: what we do not yet know about how people run to catch a ball.

Linear optic trajectory theory claims that people catch balls by running in a direction that keeps an optic trajectory of the ball linear. The authors show a range of ball trajectories for which departures of the optic trajectory from linearity do not predict which direction people will run, and the direction they choose does not correct these departures. Data from a wide range of ball trajectories show that people run so that the angle of elevation of gaze to the ball increases at a decreasing rate. But it is not yet known why people choose the particular path they do from the many that would achieve this.