Figure 1.

Flight trajectory and yaw angles. A, Horizontal projection of a flight trajectory with head position (arrow bases) and head yaw (arrow direction) shown every 25 ms. The gray dots mark the midpoints of saccades, which are numbered for the purpose of reference. The flight arena is a cage with dimensions of 40 × 40 × 40 cm³, with images of herbage covering the walls. The position of the walls is at x, y = -20, +20 cm. The total length of a typical blowfly is ∼1 cm, ∼50% longer than the arrows shown in the figure. B, Black line, Head yaw angle (rotation around its vertical axis) for the flight shown in A; gray line, track direction (tangent of path projected on a horizontal plane) for the flight shown in A. The yaw defined by the track direction, combined with zero roll, fixed pitch, and original x, y, z coordinates, yields the without-saccades stimulus variant.