Control of body position of a stick insect standing on uneven surfaces

Abstract

When a multi-legged animal walks over uneven surfaces, each leg has to span a different distance between body and ground. Thus the animal has to solve the problem of how to control the body height, i.e. to coordinate the movement of the legs in such a way that the vertical projections of leg lengths match these distances. For the standing animal, this is investigated here by testing twelve different substrate configurations and measuring body height and forces applied by the legs on the substrate. The results are consistent with the hypothesis that the legs can be considered to represent independent height controllers. They can be understood as proportional controllers with nonlinear characteristics. The mechanical coupling between the leg is sufficient to explain the experimental results. Thus, no neuronal coupling has to be assumed to exist between these controllers. This agrees with a hypothesis proposed earlier for walking animals (Cruse 1976).