Estimating body pitch from distributed proprioception in a hexapod

Gollin A, Dürr V. Estimating body pitch from distributed proprioception in a hexapod. In: Vasiliki V, ed. Biomimetic and Biohybrid Systems. 7th International Conference, Living Machines 2018, Paris, France, July 17–20, 2018, Proceedings . Lecture Notes in Computer Science. Vol 10928. Cham: Springer; 2018: 187-199.Adaptability of legged locomotion relies on distributed proprioceptive feedback from the legs. Apart from low-level control of leg movements, proprioceptive cues may also be integrated to estimate overall locomotion parameters relevant to high-level control of behavior. For example, this couldbe relevant for reliable estimates of body inclination relative to the substrate, particularly in animals that lack dedicated graviceptors such as statocycsts. With regard to robotic systems, distributed proprioception could exploit physical interaction with the substrate to improve the robustness of inclinationestimates. In insect locomotion, it is unknown how overall parameters such as body inclination or forward velocity may be represented in the nervous system. If proprioceptive encoding was optimal, the afferent activity pattern of distributed proprioceptive cues from across the body should be a suitablerepresentation in itself. However, given noisy encoding in multiple afferent spike trains, it is unknown (i) how reliable the parameter estimates can be, and (ii) which parts of a distributed proprioceptive code are most relevant. Here we use a database on unrestrained whole-body kinematics of walkingand climbing stick insects in conjunction with simple spiking proprioceptor models to transform sets of joint angle time courses into corresponding sets of spike trains. In total, we tested four different types of models: a reference model without proprioceptive encoding and three proprioception models with differentfilter properties and spike generators. Within each model, we compared 4x4 conditions that differed in number and combination of joints and legs. Our results show that the contribution of middle and hind legs is of similar relevance for the estimation of body pitch, whereas front legs contribute only very little.Furthermore, femoral levation proved to be the most relevant degree of freedom, whereas estimates based on protraction and extension angles were less accurate