Pursuit altering the direction of a trajectory. Pursuit behaviour results from the movement of an attractor. In this case, the direction of the trajectory is altered since the attractor moves against the flow. Upper panels show (quasi-)potential surfaces, lower panels phase portraits as in Figure 3C. The progress of time is shown through increasingly dark shading, and by the arrow at the bottom of the figure. (A–D) Panels show the movement of the attractors towards the origin as activation strength (represented by α
in equation 1) is decreased over time. As the attractor ‘overtakes’ the trajectory (between panels B and C), the angle of the flow changes drastically, leading to a reversal in the direction of the trajectory (clearly visible in D). See also Additional file 3, Supporting Movie S3.