Single whisker representations in the circuitry of the cerebellar cortex

The cerebellum plays a crucial role in sensorimotor processing, yet little is known about its contribution towards sensory signal processing. The whisking behaviour in rodents is a model behaviour for sensorimotor function and the Crus I and II lob ules of the cerebellum have been shown to represent perioral stimulation, linearly encoded whisker setpoint and be important in the generation of whisker movement. To target our investigation of the sensory representation, I have used a very nar rowly defined stimulus, the deflection of a single whisker, to investigate the re sponse in cerebellar cortex neurons using whole-cell and cell-attached patch-clamp. In the first step of cerebellar cortex processing, I found the convergence in individual granule cell of mossy fibre inputs at latencies indicating a direct pathway through the trigeminal nuclei and a cortico-pontine path for the single whisker signal. Mo lecular layer interneurons were found to be highly precisely and rapidly excited by the early direct path input from granule cells. Lateral inhibition was also displayed by a molecular layer interneuron with an inhibitory response. The sole output of the cerebellar cortex, the Purkinje cells, exhibited simple spike responses often combining excitatory and inhibitory phases in the majority of rec orded cells despite the narrowness of the stimulus and the wide recording location. A complex spike response was measured in half of the Purkinje cells with a simple 7 response and never in Purkinje cell without simple spike responses. This separation of the Purkinje cell population into neurons receiving both mossy fibre and climbing fibre input on the single whisker deflection and those that only receive mossy fibre input suggest different mechanisms (e.g. plasticity) and functions. Together, these findings quantify the sensory input to the cerebellar cortex follow ing a single whisker deflection and the downstream processing of this signal.Open Acces

Experimental Performance of a Solar Air Collector with a Perforated Back Plate in New Zealand

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Motion constraint

In this paper, we propose a hybrid postural control approach taking advantage of data-driven and goal-oriented methods while overcoming their limitations. In particular, we take advantage of the latent space characterizing a given motion database. We introduce a motion constraint operating in the latent space to benefit from its much smaller dimension compared to the joint space. This allows its transparent integration into a Prioritized Inverse Kinematics framework. If its priority is high the constraint may restrict the solution to lie within the motion database space. We are more interested in the alternate case of an intermediate priority level that channels the postural control through a spatiotemporal pattern representative of the motion database while achieving a broader range of goals. We illustrate this concept with a sparse database of large range full-body reach motion

Collision detection algorithm

International audienceFor many years, collision detection has been of major interest in robotics and computer graphics. Numerous approaches have been investigated to detect interfering objects in applications such as robot task planning, computational biology, games, surgery simulation, and cloth simulation. The central physical concept is spatial exclusion, i.e. the fact that two physical objects cannot occupy the same spatial location. In the context of virtual computer-simulated objects, the spatial exclusion principle must be implemented through specific algorithms

Dynamic obstacle avoidance for real-time character animation

This paper proposes a novel method to control virtual characters in dynamic environments. A virtual character is animated by a locomotion and jumping engine, enabling production of continuous parameterized motions. At any time during runtime, flat obstacles (e.g. a puddle of water) can be created and placed in front of a character. The method first decides whether the character is able to get around or jump over the obstacle. Then the motion parameters are accordingly modified. The transition from locomotion to jump is performed with an improved motion blending technique. While traditional blending approaches let the user choose the transition time and duration manually, our approach automatically controls transitions between motion patterns whose parameters are not known in advance. In addition, according to the animation context, blending operations are executed during a precise period of time to preserve specific physical properties. This ensures coherent movements over the parameter space of the original input motions. The initial locomotion type and speed are smoothly varied with respect to the required jump type and length. This variation is carefully computed in order to place the take-off foot as close to the created obstacle as possibl

Robust on-line adaptive footplant detection and enforcement for locomotion

A common problem in virtual character computer animation concerns the preservation of the basic foot-floor constraint (or footplant), consisting in detecting it before enforcing it. This paper describes a system capable of generating motion while continuously preserving the footplants for a real-time, dynamically evolving context. This system introduces a constraint detection method that improves classical techniques by adaptively selecting threshold values according to motion type and quality. The footplants are then enforced using a numerical inverse kinematics solver. As opposed to previous approaches, we define the footplant by attaching to it two effectors whose position at the beginning of the constraint can be modified, in order to place the foot on the ground, for example. However, the corrected posture at the constraint beginning is needed before it starts to ensure smoothness between the unconstrained and constrained states. We, therefore, present a new approach based on motion anticipation, which computes animation postures in advance, according to time-evolving motion parameters, such as locomotion speed and type. We illustrate our on-line approach with continuously modified locomotion patterns, and demonstrate its ability to correct motion artifacts, such as foot sliding, to change the constraint position and to modify from a straight to a curved walk motio

On scaling strategies for the full-body postural control of virtual mannequins

Due to its intrinsic complexity, full-body postural input has been mostly limited to off-line motion capture and to on-line puppetry of a virtual character with little interaction with its environment (e.g. floor). The motion capture technology is now mature enough to envision the on-line full-body postural control of virtual mannequins involved in precise reaching tasks. We have investigated such tasks for mannequins of differing body heights in comparison to that of the system user. Such broad-range avatar control is relevant for virtual prototyping in various industrial sectors as a single person is responsible for evaluating a virtual prototype for a full range of potential end-users. In the present paper we report on two scaling strategies that can be enforced in such a context of height-differing avatar control. Both scaling strategies have been evaluated in a wide-range reach study both in front of a stationary immersive display and with an HMD. A comparison is also made with a baseline scenario, which exploits a simple rigid shape (i.e. a proxy), to assess the specific influence of controlling a complex articulated avata

Proactive Steering Toward Oriented Targets

In this paper we introduce a real-time steering controller ensuring the reach of a (possible mobile) target position and orientation, without requiring to build/update the full trajectory to that target. We name it the funnelling control. The final orientation is achieved through the continuous adjustment of the heading direction. This control mode is proactive in the sense that it anticipates the success/failure of the reach and adjusts the desired speed accordingly. Both features rely on an heterogeneously sampled table of radial-tangential seek angles obtained when the controller reaches a desired position target without prescribed orientation. By construction, the control update has a constant computing cost, even with variable target characteristics. Its low update cost makes it particularly suited for controlling a large number of mobile entities in real-time. The present exposition is made for an obstacle-free context

Relaxed Steering towards Oriented Region Goals

This paper extends the funnelling behavior to offer a low-cost flexible guidance of mobile entities towards a circular region goal with the guarantee of enforcing an orientation within a predefined tolerance interval. The key requirements are the same as the tunnelling control, i.e. a low and constant cost update of the control even when the goal parameters change (distance and relative orientation of the goal, position tolerance radius, orientation tolerance interval, desired speed). The smoothness and the optimality of the resulting trajectory being of high importance the paper qualitatively compares the trajectories produced by both tunnelling algorithms. The new relaxed approach appears to produce smoother and shorter path for path made of a succession of large region goals. These qualities and its low cost advocate for its exploitation for moving through large dynamically changing regions without precise a priori planning