scholarly journals Experimental and theoretical study of velocity fluctuations during slow movements in humans

2019 ◽  
Vol 121 (2) ◽  
pp. 715-727 ◽  
Author(s):  
Emmanuel Guigon ◽  
Oussama Chafik ◽  
Nathanaël Jarrassé ◽  
Agnès Roby-Brami
Keyword(s):  
Control Process ◽  
Arm Movement ◽  
Velocity Profiles ◽  
Optimal Feedback Control ◽  
Movement Speed ◽  
Velocity Fluctuations ◽  
Model Driven ◽  
Movement Trajectories ◽  
Position Signal ◽  
Constant Duration

Moving smoothly is generally considered as a higher-order goal of motor control and moving jerkily as a witness of clumsiness or pathology, yet many common and well-controlled movements (e.g., tracking movements) have irregular velocity profiles with widespread fluctuations. The origin and nature of these fluctuations have been associated with the operation of an intermittent process but in fact remain poorly understood. Here we studied velocity fluctuations during slow movements, using combined experimental and theoretical tools. We recorded arm movement trajectories in a group of healthy participants performing back-and-forth movements at different speeds, and we analyzed velocity profiles in terms of series of segments (portions of velocity between 2 minima). We found that most of the segments were smooth (i.e., corresponding to a biphasic acceleration) and had constant duration irrespective of movement speed and linearly increasing amplitude with movement speed. We accounted for these observations with an optimal feedback control model driven by a staircase goal position signal in the presence of sensory noise. Our study suggests that one and the same control process can explain the production of fast and slow movements, i.e., fast movements emerge from the immediate tracking of a global goal position and slow movements from the successive tracking of intermittently updated intermediate goal positions. NEW & NOTEWORTHY We show in experiments and modeling that slow movements could result from the brain tracking a sequence of via points regularly distributed in time and space. Accordingly, slow movements would differ from fast movement by the nature of the guidance and not by the nature of control. This result could help in understanding the origin and nature of slow and segmented movements frequently observed in brain disorders.

scholarly journals Targeting in Virtual Workspaces: motor learning consolidates spatial memory for performance clusters

2019 ◽  
Author(s):  
Bradly Alicea ◽  
Corey Bohil ◽  
Frank Biocca ◽  
Charles Owen
Keyword(s):  
Repeated Measures ◽  
Target Location ◽  
Movement Time ◽  
Three Dimensional ◽  
Arm Movement ◽  
Hierarchical Cluster ◽  
Movement Speed ◽  
Advantages And Disadvantages ◽  
Training Interval ◽  
Speed And Accuracy

Our objective was to focus on linkages between the process of learning and memory and the placement of objects within an array of targets in a virtual workspace. Participants were instructed to place virtual objects serially within a three-dimensional target array. One phase presented each target sequentially, and required participants to make timed ballistic arm movements. The other phase presented all nine targets simultaneously, which required ballistic arm movement towards the correct target location as recalled from the learning phase. Movement time and accuracy were assessed using repeated-measures ANOVA, a hierarchical cluster analysis, and a multiple linear regression. Collectively, this revealed numerous speed and accuracy advantages and disadvantages for various positional combinations. Upper positions universally yielded longer movement times and larger error measurements. Individual ability for mental rotation combined with task learning over a fixed training interval was found to predict accuracy for specific locations. The prediction that location influences movement speed and accuracy was supported, but with some caveats. These results may be particularly useful in the design of instructor stations and other hybrid physical-virtual workspaces.

Are Complex Control Signals Required for Human Arm Movement?

1998 ◽  
Vol 79 (3) ◽  
pp. 1409-1424 ◽  
Author(s):  
Paul L. Gribble ◽  
David J. Ostry ◽  
Vittorio Sanguineti ◽  
Rafael Laboissière
Keyword(s):  
Joint Stiffness ◽  
Arm Movement ◽  
Movement Speed ◽  
Muscle Properties ◽  
Complex Control ◽  
Equilibrium Trajectory ◽  
Control Signals ◽  
Human Arm ◽  
Constant Rate ◽  
Arm Motion

Gribble, Paul L., David J. Ostry, Vittorio Sanguineti, and Rafael Laboissière. Are complex control signals required for human arm movement? J. Neurophysiol. 79: 1409–1424, 1998. It has been proposed that the control signals underlying voluntary human arm movement have a “complex” nonmonotonic time-varying form, and a number of empirical findings have been offered in support of this idea. In this paper, we address three such findings using a model of two-joint arm motion based on the λ version of the equilibrium-point hypothesis. The model includes six one- and two-joint muscles, reflexes, modeled control signals, muscle properties, and limb dynamics. First, we address the claim that “complex” equilibrium trajectories are required to account for nonmonotonic joint impedance patterns observed during multijoint movement. Using constant-rate shifts in the neurally specified equilibrium of the limb and constant cocontraction commands, we obtain patterns of predicted joint stiffness during simulated multijoint movements that match the nonmonotonic patterns reported empirically. We then use the algorithm proposed by Gomi and Kawato to compute a hypothetical equilibrium trajectory from simulated stiffness, viscosity, and limb kinematics. Like that reported by Gomi and Kawato, the resulting trajectory was nonmonotonic, first leading then lagging the position of the limb. Second, we address the claim that high levels of stiffness are required to generate rapid single-joint movements when simple equilibrium shifts are used. We compare empirical measurements of stiffness during rapid single-joint movements with the predicted stiffness of movements generated using constant-rate equilibrium shifts and constant cocontraction commands. Single-joint movements are simulated at a number of speeds, and the procedure used by Bennett to estimate stiffness is followed. We show that when the magnitude of the cocontraction command is scaled in proportion to movement speed, simulated joint stiffness varies with movement speed in a manner comparable with that reported by Bennett. Third, we address the related claim that nonmonotonic equilibrium shifts are required to generate rapid single-joint movements. Using constant-rate equilibrium shifts and constant cocontraction commands, rapid single-joint movements are simulated in the presence of external torques. We use the procedure reported by Latash and Gottlieb to compute hypothetical equilibrium trajectories from simulated torque and angle measurements during movement. As in Latash and Gottlieb, a nonmonotonic function is obtained even though the control signals used in the simulations are constant-rate changes in the equilibrium position of the limb. Differences between the “simple” equilibrium trajectory proposed in the present paper and those that are derived from the procedures used by Gomi and Kawato and Latash and Gottlieb arise from their use of simplified models of force generation.

Physical activity as the main factor affecting body composition of the visually impaired

Physiotherapy ◽  
2017 ◽  
Vol 25 (1) ◽  
Author(s):  
Anita Olszewska ◽  
Anna Jackowiak ◽  
Agnieszka Chwałczyńska ◽  
Krzysztof A. Sobiech
Keyword(s):  
Physical Activity ◽  
Body Composition ◽  
Physical Fitness ◽  
Visually Impaired ◽  
Arm Movement ◽  
Lower Limbs ◽  
Movement Speed ◽  
Abdominal Muscles ◽  
Blind And Visually Impaired ◽  
The Right

AbstractThe aim of the study was to determine how physical activity affected the physical fitness and body composition of the blind and visually impaired.The study included 28 male students from the Lower Silesia Special Educational Centre No. 13 for the Blind and Visually Impaired in Wroclaw, aged 18–22 years, with disability degree certificates. The subjects were divided into two groups: physically active men (TR,Men engaging in additional forms of physical activity presented significant (Additional physical activity undertaken by the visually impaired has a positive effect on their physical fitness, namely and primarily on their flexibility, functional strength, speed, arm movement speed, jumping ability, and the strength of the abdominal muscles. Moreover, additional physical activity significantly affects the overall and segmental body composition in the lower limbs and the right upper limb.

The structure and development of a wing-tip vortex

1996 ◽  
Vol 312 ◽  
pp. 67-106 ◽  
Author(s):  
William J. Devenport ◽  
Michael C. Rife ◽  
Stergios I. Liapis ◽  
Gordon J. Follin
Keyword(s):  
Flow Structure ◽  
Velocity Profiles ◽  
Tip Vortex ◽  
Mean Velocity ◽  
Velocity Fluctuations ◽  
The Core ◽  
Show Evidence ◽  
Vortex Centre ◽  
Velocity Spectra ◽  
Naca 0012

Experiments have been performed on the tip vortex trailing from a rectangular NACA 0012 half-wing. Preliminary studies showed the vortex to be insensitive to the introduction of a probe and subject only to small wandering motions. Meaningful velocity measurements could therefore be made using hot-wire probes.Detailed analysis of the effects of wandering was performed to properly reveal the flow structure in the core region and to give confidence in measurements made outside the core. A theory has been developed to correct mean-velocity profiles for the effects of wandering and to provide complete quantitative estimates of its amplitude and contributions to Reynolds stress fields. Spectral decomposition was found to be the most effective method of separating these contributions from velocity fluctuations due to turbulence.Outside the core the flow structure is dominated by the remainder of the wing wake which winds into an ever-increasing spiral. There is no large region of axisymmetric turbulence surrounding the core and little sign of turbulence generated by the rotational motion of the vortex. Turbulence stress levels vary along the wake spiral in response to the varying rates of strain imposed by the vortex. Despite this complexity, the shape of the wake spiral and its turbulent structure reach an approximately self-similar form.On moving from the spiral wake to the core the overall level of velocity fluctuations greatly increases, but none of this increase is directly produced by turbulence. Velocity spectra measured at the vortex centre scale in a manner that implies that the core is laminar and that velocity fluctuations here are a consequence of inactive motion produced as the core is buffeted by turbulence in the surrounding spiral wake. Mean-velocity profiles through the core show evidence of a two-layered structure that dies away with distance downstream.

Linear optimal control applied to instabilities in spatially developing boundary layers

2002 ◽  
Vol 470 ◽  
pp. 151-179 ◽  
Author(s):  
MARKUS HÖGBERG ◽  
DAN S. HENNINGSON
Keyword(s):  
Optimal Control ◽  
Cross Flow ◽  
Velocity Profiles ◽  
Base Flow ◽  
Optimal Feedback Control ◽  
Linear Optimal Control ◽  
Convolution Kernels ◽  
Tollmien Schlichting ◽  
Layer Flow ◽  
Parallel Case

The work presented extends previous research on linear controllers in temporal channel flow to spatially evolving boundary layer flow. The flows studied are those on an infinite swept wedge described by the Falkner–Skan–Cooke (FSC) velocity profiles, including the special case of the flow over a flat plate. These velocity profiles are used as the base flow in the Orr–Sommerfeld–Squire equations to compute the optimal feedback control through blowing and suction at the wall utilizing linear optimal control theory. The control is applied to a parallel FSC flow with unstable perturbations. Through an eigenvalue analysis and direct numerical simulations (DNS), it is shown that instabilities are stabilized by the controller in the parallel case. The localization of the convolution kernels for control is also shown for the FSC profiles.Assuming that non-parallel effects are small a technique is developed to apply the same controllers to a DNS of a spatially evolving flow. The performance of these controllers is tested in a Blasius flow with both a Tollmien–Schlichting (TS) wave and an optimal spatial transiently growing perturbation. It is demonstrated that TS waves are stabilized and that transient growth is lowered by the controller. Then the control is also applied to a spatial FSC flow with unstable perturbations leading to saturated cross-flow vortices in the uncontrolled case. It is demonstrated that the linear controller successfully inhibits the growth of the cross-flow vortices to a saturated level and thereby delays the possibility of transition through secondary instabilities. It is also demonstrated that the controller works for relatively high levels of nonlinearity, and for stationary as well as time-varying perturbations.

scholarly journals Can proprioceptive training improve motor learning?

2012 ◽  
Vol 108 (12) ◽  
pp. 3313-3321 ◽  
Author(s):  
Jeremy D. Wong ◽  
Dinant A. Kistemaker ◽  
Alvin Chin ◽  
Paul L. Gribble
Keyword(s):  
Motor Learning ◽  
Visual Information ◽  
Movement Control ◽  
Arm Movement ◽  
Sensory Function ◽  
Movement Speed ◽  
Active Movement ◽  
Positional Accuracy ◽  
Control Subjects ◽  
Proprioceptive Training

Recent work has investigated the link between motor learning and sensory function in arm movement control. A number of findings are consistent with the idea that motor learning is associated with systematic changes to proprioception (Haith A, Jackson C, Mial R, Vijayakumar S. Adv Neural Inf Process Syst 21: 593–600, 2008; Ostry DJ, Darainy M, Mattar AA, Wong J, Gribble PL. J Neurosci 30: 5384–5393, 2010; Vahdat S, Darainy M, Milner TE, Ostry DJ. J Neurosci 31: 16907–16915, 2011). Here, we tested whether motor learning could be improved by providing subjects with proprioceptive training on a desired hand trajectory. Subjects were instructed to reproduce both the time-varying position and velocity of novel, complex hand trajectories. Subjects underwent 3 days of training with 90 movement trials per day. Active movement trials were interleaved with demonstration trials. For control subjects, these interleaved demonstration trials consisted of visual demonstration alone. A second group of subjects received visual and proprioceptive demonstration simultaneously; this group was presented with the same visual stimulus, but, in addition, their limb was moved through the target trajectory by a robot using servo control. Subjects who experienced the additional proprioceptive demonstration of the desired trajectory showed greater improvements during training movements than control subjects who only received visual information. This benefit of adding proprioceptive training was seen in both movement speed and position error. Interestingly, additional control subjects who received proprioceptive guidance while actively moving their arm during demonstration trials did not show the same improvement in positional accuracy. These findings support the idea that the addition of proprioceptive training can augment motor learning, and that this benefit is greatest when the subject passively experiences the goal movement.

scholarly journals Evaluating Arm Movement Imitation

2006 ◽  
Vol 4 (4) ◽  
Author(s):  
Alexandra Constantin ◽  
Maja Matarić
Keyword(s):  
Empirical Study ◽  
Arm Movement ◽  
Pairwise Similarity ◽  
Rotational Angle ◽  
Movement Trajectories ◽  
Human Evaluation ◽  
Movement Imitation

In this paper, we present a metric for assessing the quality of arm movement imitation. We develop a joint-rotational-angle-based segmentation and comparison algorithm that rates pairwise similarity of arm movement trajectories on a scale of 1-10. We describe an empirical study designed to validate the algorithm we developed, by comparing it to human evaluation of imitation. The results provide evidence that the evaluation of the automatic metric did not significantly differ from human evaluation.

scholarly journals How do Reaction Time and Movement Speed Depend on the Complexity of the Task?

2018 ◽  
Vol 2 (69) ◽  
Author(s):  
Dalia Mickevičienė ◽  
Kristina Motiejūnaitė ◽  
Albertas Skurvydas ◽  
Tomas Darbutas ◽  
Diana Karanauskienė
Keyword(s):  
Reaction Time ◽  
High Speed ◽  
Arm Movement ◽  
Movement Speed ◽  
Dynamic Parameters ◽  
Target Movement ◽  
Simple Task ◽  
High Performing ◽  
The Right ◽  
Complicated Task

The aim of the research was to determine how the reaction time and the movement speed depend on the complexity of the task. The research was carried out in the Laboratory of Human Motor Control at the Lithuanian Academy of Physical Education (LAPE) applying the analyzer of dynamic parameters of human leg and arm movement (DPA-1; Patent No. 5251; 2005 08 25), which is used for the qualitative estimation of the dynamic parameters of one arm and leg target movement, two arms and legs coordinated and independent target movements, when the resistance power and target are coded with different programmable parameters. We registered the reaction time (RT) and the movement speed (Vmax) performing simple tasks of reaction and speed and a complicated task of accuracy. Research results indicated that performing a complicated task the reaction is slower, and the maximal movement speed is lower than performing a simple task. However, it does not mean that movement speed will be higher when the reaction is faster performing a simple task. The data obtained confirmed Hick’s law proposing that reaction time is directly proportional to the complexity of the task because performing the tasks of different levels of complexity the reaction time values of the right arm were statistically significantly different (p < 0.001). After performing the analysis of variation coefficients we established that the highest coefficient of variation was received from the indices of movement speed performing a speed task (23%), and the lowest — of reaction time performing a reaction task (10%). The obtained results confirm other authors’ suggestion that performing a complicated task the reaction time is a more steadily controlled index than maximal movement speed. A strong correlation was determined between the reaction time values performing the tasks of reaction and accuracy, but there was no statistical link between the maximal speed values performing the tasks of speed and accuracy. This indicates that if the movement speed is high performing a simple task, it does not mean that it will be high performing a complicated task. Conclusions: 1) performing a complicated task reaction time is longer, and maximal movement speed is lower than performing a simple task; 2) the complexity of the task more impacts the dispersion of results of the movement speed than of the reaction time; 3) high speed performing a simple task does not indicate that it will be high performing a complicated task.Keywords: reaction time, movement speed, the complexity of the task.

scholarly journals The interplay between movement, dispersal and morphology in Tetrahymena ciliates

2018 ◽  
Author(s):  
Frank Pennekamp ◽  
Jean Clobert ◽  
Nicolas Schtickzelle
Keyword(s):  
Model Organism ◽  
Spatial Location ◽  
Morphological Properties ◽  
Movement Speed ◽  
Movement Behaviour ◽  
Dispersal Rate ◽  
Movement Trajectories ◽  
Spatio Temporal ◽  
Path Tortuosity

Understanding how and why individual movement translates into dispersal between populations is a long-term goal in ecology. Movement is broadly defined as “any change in the spatial location of an individual”, whereas dispersal is more narrowly defined as a movement that may lead to gene flow. Because the former may create the condition for the latter, behavioural decisions that lead to dispersal may be detectable in underlying movement behaviour. In addition, dispersing individuals also have specific sets of morphological and behavioural traits that help them coping with the costs of movement and dispersal, and traits that mitigate costs should be under selection and evolve if they have a genetic basis. Here we experimentally study the relationships between movement behaviour, morphology and dispersal across 44 genotypes of the actively dispersing unicellular, aquatic model organism Tetrahymena thermophila. We used two-patch populations to quantify individual movement trajectories, as well as activity, morphology and dispersal rate. First, we studied variation in movement behaviour among and within genotypes (i.e. between dispersers and residents) and tested whether this variation can be explained by morphology. Then, we address how much the dispersal rate is driven by differences in the underlying movement behaviour. Genotypes expressed different movements in terms of speed and path tortuosity. We also detected marked movement differences between resident and dispersing individuals, mediated by the genotype. Movement variation was partly explained by morphological properties such as cell size and shape, with larger cells consistently showing higher movement speed and lower tortuosity. Genetic differences in activity and diffusion rates were positively related to the observed dispersal and jointly explained 45% of the variation in dispersal rate. Our study shows that a detailed understanding of the interplay between morphology, movement and dispersal may have potential to improve dispersal predictions over broader spatio-temporal scales.

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