Fig. 2. Stance trajectories and gait pattern change during turning. (A) Stance trajectories of the tibia–tarsus joint on the surface of the sphere, drawn relative to the tethered body. Trajectories are largely parallel to the body axis during straight walking (Ai; before stimulus motion) but of different length and orientation during curve walking (Aii; during stimulus motion). Same trial as in Fig. 1. Each line shows a stance trajectory in body-centred coordinates, with the animal facing to the right. Circles labelled T1, T2 and T3 mark the location of the coxae of the first, second and third thorax segment, respectively. Horizontal dotted reference lines are drawn parallel to the body long axis. Left and right legs are outside and inside the curvature, respectively. For clarity, stance trajectories of middle legs are shown in grey. Numbered arrows on the lower panel indicate selected start- or endpoints of the first and second trajectories after onset of visual motion. (B) The stepping pattern of the same trial as in A. Horizontal line segments depict stance phases of a given leg. O1, O2 to O3 denote outer front, middle and hind legs, respectively (left legs). I1 to I3 denote corresponding inner legs (right legs). Steps that started during the stimulus period are shown in grey.