Measuring large obstacle traversal over large spatiotemporal scales

Animals traverse large obstacles in complex 3-D terrain by using physical interaction to make diverse locomotor transitions. Understanding how such transitions emerge is challenging, especially at large spatiotemporal scales. Existing terrain testbeds limit observations to small scales (~10 strides or body lengths). Here, we used a novel terrain treadmill to study cockroach traversal of large pillar obstacles over large spatiotemporal scales. Our treadmill consists of a transparent outer sphere and a concentric inner sphere mounted with large pillars and is controlled to keep an untethered animal moving on top. Animals moved on the treadmill freely and continuously, even up to ~500 seconds (250× increase), covering ~50 m (20× increase), while changing direction freely. We reconstructed its 3-D motion to measure the body/antenna contact with obstacles. For sparse pillars, body-pillar interaction was minimal due to wider gaps and antennae use to detect and avoid obstacles. For cluttered pillars, animals interacted and rolled its body into gap and traversed. Behavior such as antenna sweeping, body turning, and pillar climbing were also observed. Our experimental system can measure locomotor behaviors with a high spatial resolution over a long duration and distance.