Comparative physiology and biomechanics are our areas of interest. We quantify whole animal performance and address its mechanistic bases. We focus primarily on locomotor performance because it is a readily quantifiable behavior which often has ecological and evolutionary significance. Our research program deals with the energetics and dynamics of terrestrial locomotion.
An understanding of diverse animals promises to yield the “architectural secrets” that will aid in the development of a general theory of animal locomotion and animal design. General principles can then be used as hypotheses to explain the remarkable diversity in physiology and morphology. Diversity enables discovery.
Diversity of organisms. Our approach is not limited to a particular group of animals. However, the study of arthropod, amphibian and reptilian locomotion has proved to be most rewarding. It is very important to realize that we do not study these animals simply because we want to know something about how they move, although many of them do have an important impact on ecology (such as being pests or to be used as a bio-control agent). We study them to discover general principles about how muscles and skeletons work. We do not study them because we like them. Many of them are actually disgusting, but they tell us secrets of nature that we cannot find out from studying one species, like humans.
Title: Multifunctionality in ghost crabs [Dwight Springthorpe]
In collaboration with Dan Goldman’s lab at Georgia Tech (link: http://crablab.gatech.edu/ )
Ghost crabs are remarkably multifunctional animals. They are capable of running, climbing, capturing prey and burrowing- all with the same set of relatively simple appendages. Among these behaviors, burrowing is of particular interest because it represents a complex suite of behaviors including specialized postures, locomotion in confined environments and goal-directed manipulation of the substrate. By using novel x-ray imaging methods, we recently gained new insight into the crabs’ burrowing strategies, finding that burrowing crabs possess a broad toolkit. Burrowing involves hook-and-pull motions (similar to the excavation behavior observed in ant eaters), scratch digging (as found in many rodents), body rotations and highly coordinated movements to manipulate collected substrate. Ongoing work focuses on how these behaviors change with substrate properties and how these crabs are able to use their limbs for such diverse tasks. Results will offer insight into the general principles of animal multifunctionality and inspire a new generation of bio-inspired robots, capable of navigating complex obstacles through multimodal locomotive and manipulative strategies.
Control via inertial appendage during rapid locomotion [Tom Libby]
The amazing mobility of small animals is certainly due in part to interactions between their limbs and the substrate as they run and climb. Equally important is their stability during transitions, for example during short leaps or falls. Without the ability to push on the environment, lizards turn to their tails for control – accelerating the inertia of their large caudal appendages results in a counter-torque on their bodies, which they can use to maneuver.
When perturbed during a leap, lizards control the swing of their tails in a measured manner to redirect angular momentum from their bodies to their tails, stabilizing body attitude in the sagittal plane. Our dynamics model revealed that an animal swinging its tail experienced less rotation than a body with a rigid tail, a passively compliant tail or no tail. Moreover, we found that tail swing correlated with perturbation size and direction, indicating that lizards use proportional feedback control. To examine a known controlled tail response, we built a lizard-sized robot with an active tail that used sensory feedback to stabilize pitch as it drove off a ramp. This relatively simple machine has inspired active tails on a number of more sophisticated robots, including XRL, the latest version of RHex.
View related movies and images at:
Interaction between sensor and movement during active sensing task [Jean-Michel Mongeau]
When actively sensing, animals can expend energy to acquire information by emitting signals or moving sensory structures. However, it is not clear if the energy from locomotion, itself, could permit a different form of active sensing where animals transfer the energy from movement to reconfigure a passive sensor. During rapid tasks such as high-speed locomotion, the whole sensory apparatus of animals is propelled through the environment while operating on a moving body. Using a combination of behavioral and robotic experiments with LIMBS lab, we have demonstrated that cockroaches can transfer the self-generated energy from locomotion to actively control the state of the antenna via passive mechanical elements (i.e. hairs) with important effects on body control. Here, we have broadened the definition of active sensing to include sensing mediated by passive sensor-environment interactions with locomotion as the energy source. This project advances our current understanding of active sensing by showing how the whole body, and not just the sensor, can participate in sensory acquisition.
Collaborators: Alican Demir, Noah Cowan (LIMBS lab, Johns Hopkins University)
Information flow from individual sensory units operating on moving body [Jean-Michel Mongeau]
Information flow from individual sensory units operating on locomotion-driven appendages to the generation of motor patterns is not well understood. The nervous system must integrate sensory information from noisy channels while constrained by neural conduction delays. When performing high-speed wall following using their antennae, cockroaches integrate information from body-to-wall distance and generate appropriate turns to prevent collisions. Previous work on modeling high-speed wall following predicted that a sensory controller for antenna tactile sensing of wall position (P) and the derivative of position (D) was sufficient for control of the body. I hypothesized that individual mechanoreceptive units along the antenna were tuned to enable stable running. Extracellular multi-unit recordings revealed P and D sensitivity and variable-latency responses suggesting the antenna functions as a delay line. This study revealed how individual sensor units distributed on a sensor array precondition neural signals for the control of a dynamical, moving body.
Collaborators: Simon Sponberg (University of Washington), John Miller (Montana State University)
Neuro-mechanical processing: mechanical tuning of sensory appendage [Jean-Michel Mongeau]
As sensors of animals are embedded within the body, they must function through the mechanical properties of the body. In addition, it is critical to understand how the body drives sensory appendages to understand how mechanics condition neural encoding. I have studied mechanical properties of the primary tactile sensors of cockroaches, the antennae, using a combination of experimental, computational and robotic techniques in collaboration with the LIMBS lab. I have revealed how both the static and dynamic properties of the antenna influence sensory acquisition during quasi-static and dynamic sensorimotor tasks. Further elucidating antennal mechanical tuning
will lead to hypotheses integrating distributed mechanosensory inputs from a dynamic sensory appendage operating on a moving body. This work has led to the design of biologically-inspired sensor to study the interaction between mechanics and sensing and this sensor is currently being interfaced to a mobile robot for tactile navigation.
Collaborators: Alican Demir, Noah Cowan (LIMBS, Johns Hopkins University)
Biomechanics of agility in small animals [Jean-Michel Mongeau]
Escaping from predators often demands that animals rapidly negotiate complex environments. The smallest animals attain relatively fast speeds with high frequency leg cycling, wing flapping or body undulations, but absolute speeds are slow compared to larger animals. Instead, small animals benefit from the advantages of enhanced maneuverability in part due to scaling. We discovered a novel behavior in small, legged runners that may facilitate their escape by disappearance from predators. We video recorded cockroaches and geckos rapidly running up an incline toward a ledge, digitized their motion and created a simple model to generalize the behavior. Both species ran rapidly at 12–15 body lengths-per-second toward the ledge without braking, dove off the ledge, attached their feet by claws like a grappling hook, and used a pendulum-like motion that can exceed one meter-per-second to swing around to an inverted position under the ledge, out of sight. We discovered geckos in Southeast Asia can execute this escape behavior in the field.
Collaborators: Ardian Jusufi, Paul Birkmeyer, Ron Fearing (Berkeley); Aaron Hoover (Olin College)
View related Quicktime movie. [Side view of a cockroach, P. americana, performing a high-speed inversion while running up a ramp. The first sequences are real time. The second sequences are slowed 10X. The last sequence is slowed 50X. doi:10.1371/journal.pone.0038003.s002]