Workshop 4: Sensori-motor control of animals and robots
Equipping simulated humans and animals with the ability to locomote and interact within physics-based simulations presents a number of interesting challenges. In this talk I will describe work on controlling style in locomotion, anticipation during balancing, and control for in-hand manipulation. I will also discuss ongoing efforts to learn control strategies from captured motion.
Decisions depend on the reward at stake and the effort required. However, these same variables influence the vigor of the ensuing movement, suggesting that factors that affect evaluation of action also influence performance of the selected action. In this talk, I will describe a mathematical framework that links decision-making with motor control. Each action has a utility that combines the reward at stake with its effort requirements, both discounted as a function of time. The critical assumption of this model is to represent effort via the metabolic energy expended to produce the movement. I will show that a single mathematical formulation of action predicts both the decisions that animals make as well as the vigor of the movements that follow. This framework accounts for choices that birds make in walking vs. flying, choices that people make in reaching and force production, and the curious fact that pedestrians walk faster in certain cities. I suggest that decision-making and movement control share a common utility in which the expected rewards and the energetic costs are discounted as a function of time.
We have recently found that people can rapidly converge upon energetically optimal gaits when immersed in novel energetic landscapes created using robotic exoskeletons. Here I will present our new research focused on uncovering the mechanisms underlying the initiation of this optimization, as well as its process.
Life in rough terrain: Integration of mechanics and sensorimotor control for agile and robustly stable bipedal locomotion.Monica Daley
Animals must precisely control limb-substrate interactions to move effectively over varied and uncertain terrain while avoiding injury. One key source of uncertainty for animals is sensorimotor delay, which limits feedback response times. My research team study perturbed and transient locomotor dynamics to understand how animals effectively integrate mechanics and sensorimotor control to overcome these challenges. We often study ground birds, because they are diverse bipeds that span >1000-fold range in body mass, yet retain consistent morphology. I will discuss some similarities and differences between human and avian bipeds, which highlight different solutions to the problem of sensorimotor delay. Recently, we have begun studying bird perching balance, to understand how balance sense is integrated with proprioception and intrinsic leg mechanics. Bird-inspired control strategies may prove useful for developing agile autonomous robots.
Zahra Aminzare, Phil Holmes
Fast running insects employ a tripod gait with three legs in swing and three in stance, while slower walkers use a tetrapod gait with two legs in swing and four in stance. Fruit flies exhibit a tetrapod to tripod transition at intermediate speeds. We study the effect of stepping frequency on such gait transitions in a bursting neuron model where each cell represents a hemi-segmental thoracic circuit of the central pattern generator. Under phase reduction, the 24 ODE bursting neuron model becomes 6 coupled phase oscillators, each corresponding to a network driving one leg. Assuming that left and right legs maintain constant phase relations, we further reduce to a system describing ipsilateral phase differences defined on a torus. We show that bifurcations occur from multiple stable tetrapod gaits to a unique stable tripod gait as speed increases, and illustrate our results using data fitted to freely walking fruit flies.