Fig. 3. Wall-following arena. (A) Two high-speed cameras were positioned above an enclosed arena. The field-of-view of each camera was centered on an observation wall. Half-silvered mirrors in front of each camera reflected light from a fiber-optic illuminator onto the retroreflective running substrate, providing a stark silhouette of the cockroach despite very low ambient light (see Fig. 4). (B) The arena viewed from above showing the two cameras' overlapping fields of view.