Fly eyes are not still: a motion illusion in Drosophila flight supports parallel visual processing.

Most animals shift gaze by a 'fixate and saccade' strategy, where the fixation phase stabilizes background motion. A logical prerequisite for robust detection and tracking of moving foreground objects, therefore, is to suppress the perception of background motion. In a virtual reality magnetic tether system enabling free yaw movement, Drosophila implemented a fixate and saccade strategy in the presence of a static panorama. When the spatial wavelength of a vertical grating was below the Nyquist wavelength of the compound eyes, flies drifted continuously and gaze could not be maintained at a single location. Because the drift occurs from a motionless stimulus - thus any perceived motion stimuli are generated by the fly itself - it is illusory, driven by perceptual aliasing. Notably, the drift speed was significantly faster than under a uniform panorama, suggesting perceptual enhancement as a result of aliasing. Under the same visual conditions in a rigid-tether paradigm, wing steering responses to the unresolvable static panorama were not distinguishable from those to a resolvable static pattern, suggesting visual aliasing is induced by ego motion. We hypothesized that obstructing the control of gaze fixation also disrupts detection and tracking of objects. Using the illusory motion stimulus, we show that magnetically tethered Drosophila track objects robustly in flight even when gaze is not fixated as flies continuously drift. Taken together, our study provides further support for parallel visual motion processing and reveals the critical influence of body motion on visuomotor processing. Motion illusions can reveal important shared principles of information processing across taxa

Rapid inversion: running animals and robots swing like a pendulum under ledges.

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. Here, we report 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. Quantification of these acrobatic behaviors provides biological inspiration toward the design of small, highly mobile search-and-rescue robots that can assist us during natural and human-made disasters. We report the first steps toward this new capability in a small, hexapedal robot

A Systemic Approach to Consider Complexity in Sawmill Modeling

The lumber industry is challenged to operate more efficiently. Sawmill systems use much equipment with various technologies and their management methods are very much influenced by size of operation, employee skills, hierarchy levels, and the high volatility of softwood lumber commodity markets. Because of interactions between the different manufacturing system components, its management becomes a complex matter. It is therefore difficult to assess the effect of given perturbations or improvements on the overall system.This study proposes a modeling approach based on the concept of system that provides a comprehensive view for modeling and analyzing sawmill systems. Adaptations of existing formalisms to represent operating, information, and decision sub-systems are put forward, while assembling these three sub-systems in an overall model gives a new vision of the sawmill and a powerful tool for systems integration. This modeling approach could be used for diagnostic as well as for sawmill improvement. Various examples are provided on the application of this approach

Neuromechanics of Maneuverability: Sensory-Neural and Mechanical Processing for the Control of High-Speed Locomotion

Maneuverability in animals is unparalleled when compared to the most maneuverable human-engineered mobile robot. Maneuverability arises in part from animals' ability to integrate multimodal sensory information with an ongoing motor program while interacting within a spatiotemporally complex world. Complicating this integration, actions from the nervous system must operate through the mechanics of the body. Since sensors and muscles are fused to a mechanical frame, mechanical processing occurs at both at the sensory (input) and motor (output) levels. To reveal the basic organization of the neural and mechanical parts of organisms during locomotion, I studied high-speed sensorimotor tasks in a remarkably maneuverable insect, the cockroach, which integrates sensory information to navigate through irregular, unpredictable environments. 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 sensing, in which animals transfer energy from movement to reconfigure a passive sensor. In the first chapter, I demonstrate that cockroaches can transfer the self-generated energy from locomotion to actively control the state of the antenna via passive mechanical elements, with important effects on body control. This chapter advances our current understanding of sensorimotor integration during rapid running by showing how the whole body, not just the sensor, can participate in sensory acquisition.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 rapidly integrate sensory information from noisy channels while constrained by neural conduction delays. When executing high-speed wall following using their antennae, cockroaches presumably integrate information between self and obstacles to generate appropriate turns, preventing collisions. Previous work on modeling high-speed wall following within a control theoretic framework 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 may function as a delay line. In the second chapter, I show how individual sensor units distributed on the antenna precondition neural signals for the control of high-speed turning.Since sensors of animals are embedded within the body, they must function through the mechanics of the body. In Chapter 3, I studied mechanical properties of the primary tactile sensors of cockroaches, the antennae, using experimental and engineering approaches. I revealed how both the static and dynamic properties of the antenna may influence sensory acquisition during quasi-static and dynamic sensorimotor tasks. Further elucidation of antennal mechanical tuning will lead to new hypotheses, integrating distributed mechanosensory inputs from a dynamic sensory appendage operating on a moving body. During rapid escape from predators, the neuromechanical system of animals is pushed to operate closer to its limits. When operating at such extremes, small animals are true escape artists benefiting from enhanced maneuverability, in part due to scaling. In Chapter 4, I show a novel neuromechanical strategy used by the cockroach P. americana and the gecko H. platyrus which may facilitate their escape when encountering a gap. Both species ran rapidly at 12-15 body lengths-per-second toward a 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. In cockroaches, I show that the behavior is mediated by a rapid claw-engagement reflex initiated during the fall. Finally, I show how the novel behavior has inspired the design of a small, hexapedal robot that can assist rescuers during natural and human-made disasters

A Systemic Approach for Sawmill Modeling

To illustrate how to perform sawmill modeling through the systemic approach, an independent sawmill and a sawmill integrated to a pulp complex were selected and modeled. Applications of a methodology for modeling the operation, information, and decision subsystems are presented. Comprehensive diagrams assembling the different subsystems for both sawmills are built.The fitness of this approach for the diagnosis of integration problems is shown. Examples of integration problems between production and administrative information systems, as well as organizational aspects of integration, are discussed. The systemic models appear to be useful tools to share a common vision of the organization and its mission

Drosophila Spatiotemporally Integrates Visual Signals to Control Saccades

Like many visually active animals, including humans, flies generate both smooth and rapid saccadic movements to stabilize their gaze. How rapid body saccades and smooth movement interact for simultaneous object pursuit and gaze stabilization is not understood. We directly observed these interactions in magnetically tethered Drosophila free to rotate about the yaw axis. A moving bar elicited sustained bouts of saccades following the bar, with surprisingly little smooth movement. By contrast, a moving panorama elicited robust smooth movement interspersed with occasional optomotor saccades. The amplitude, angular velocity, and torque transients of bar-fixation saccades were finely tuned to the speed of bar motion and were triggered by a threshold in the temporal integral of the bar error angle rather than its absolute retinal position error. Optomotor saccades were tuned to the dynamics of panoramic image motion and were triggered by a threshold in the integral of velocity over time. A hybrid control model based on integrated motion cues simulates saccade trigger and dynamics. We propose a novel algorithm for tuning fixation saccades in flies