Effects of Nerve Signal Transmission Delay in Somatosensory Reflex Modeling Based on Inverse Dynamics and Optimization

Human motion coordination is a long-standing research issue in biomechanics, and it should also have some implications for humanoid robot control. We have built a whole-body somatosensory reflex model based on our neuromusculoskeletal model and identified its parameters through non-invasive measurements and statistical analysis. Such models are crucial for analyzing and estimating signals in the nervous system. In this paper, we focus on signal transmission delay of the somatosensory reflex loop and investigate its relationship with the generalization capability of the reflex model. We obtain some sets of model parameters assuming different time delays using the data obtained from a stepping motion, and perform cross validations against stepping motions with different cycles as well as entirely different behaviors such as squat and jump. Interestingly, time delays close to the value expected from physiological properties show better cross-validation results than others. This result suggests that relatively simple reflex control can be generalized to multiple behaviors if the parameters are appropriate, and that robust control is possible even with large feedback delay.