Feedback Control as a Framework for Understanding Tradeoffs in Biology

Control theory arose from a need to control synthetic systems. From regulating steam engines to tuning radios to devices capable of autonomous movement, it provided a formal mathematical basis for understanding the role of feedback in the stability (or change) of dynamical systems. It provides a framework for understanding any system with feedback regulation, including biological ones such as regulatory gene networks, cellular metabolic systems, sensorimotor dynamics of moving animals, and even ecological or evolutionary dynamics of organisms and populations. Here we focus on four case studies of the sensorimotor dynamics of animals, each of which involves the application of principles from control theory to probe stability and feedback in an organism's response to perturbations. We use examples from aquatic (electric fish station keeping and jamming avoidance), terrestrial (cockroach wall following) and aerial environments (flight control in moths) to highlight how one can use control theory to understand how feedback mechanisms interact with the physical dynamics of animals to determine their stability and response to sensory inputs and perturbations. Each case study is cast as a control problem with sensory input, neural processing, and motor dynamics, the output of which feeds back to the sensory inputs. Collectively, the interaction of these systems in a closed loop determines the behavior of the entire system.Comment: Submitted to Integr Comp Bio

Data from: Luminance-dependent visual processing enables moth flight in low light

Animals must operate under an enormous range of light intensities. Nocturnal and twilight flying insects are hypothesized to compensate for dim conditions by integrating light over longer times. This slowing of visual processing would increase light sensitivity but should also reduce movement response times. Using freely hovering moths tracking robotic moving flowers, we showed that the moth’s visual processing does slow in dim light. These longer response times are consistent with models of how visual neurons enhance sensitivity at low light intensities, but they could pose a challenge for moths feeding from swaying flowers. Dusk-foraging moths avoid this sensorimotor tradeoff; their nervous systems slow down but not so much as to interfere with their ability to track the movements of real wind-blown flowers

Sponberg_et_al._Science_aaa3042_data

A zip file contain 9 csv data files and one readme.txt describing the data contents

Autostabilizing airframe articulation: Animal inspired air vehicle control

Abstract — The sparse sensing and limited articulation that are characteristic of human-engineered robotic systems contrast dramatically with sensorimotor systems observed in nature. Animals are richly imbued with sensors, have many points of articulation and are heavily over-actuated. In fact, the compliant nature of the body (or Plant) of most animals requires constant control input to the muscles for postural maintenance. In this study, we show how flying insects use a compliant airframe to maintain flight stability via active articulation of the frame. We first derive the equations of motion for a model flying insect, inspired by the hawkmoth, a large fast flying and agile insect. By linearizing the equations of motion about a hovering equilibrium, we demonstrate that abdominal motions are sufficient to stabilize flight on a scale of 50ms. We then tested whether these insects use the abdomen for flight control by first measuring the open-loop transfer function between visual pitch rotations and abdominal movement in a tethered moth preparation. The measured transfer function was consistent with an abdominal control strategy. We then closed the loop and found that moths actively stabilize visual pitch rotations using abdominal motion as the only control input. The behavior was robust to variations in gain and to a variety of visual stimuli. These experiments establish airframe articulation as a plausible control mechanism for active flight. I