Anisotropic tracking: evidence for automatic synergy formation in a bimanual task

Investigation of interlimb synergy has become synonymous with the study of coordination dynamics and is largely confined to periodic movement. Based on a computational approach this paper demonstrates a method of investigating the formation of a novel synergy in the context of stochastic, spatially asymmetric movements. Nine right-handed participants performed a two degrees of freedom (2D) "etch-a-sketch" tracking task where the right hand controlled the horizontal position of the response cursor on the display while the left hand controlled the vertical position. In a pre-practice 2D tracking task, measures of phase lag between the irregularly moving target and the response showed that participants controlled left and right hands independently, performance of the right hand being slightly superior to the left. Participants then undertook 4 h 16 min distributed practice of a one degree of freedom etch-a-sketch task where the target was constrained to move irregularly in only the 45 degrees direction on the display. To track such a target accurately participants had to make in-phase coupled stochastic movements of the hands. In a post-practice 2D task, measures of phase lag showed anisotropic improvement in performance, the amount of improvement depending on the direction of motion on the display. Improvement was greatest in the practised 45 degrees and least in the orthogonal 135 degrees direction. Best and worst performances were no longer in the directions associated with right and left hands independently, but in directions requiring coupled movements of the two hands. These data support the proposal that the nervous system can establish a model of novel coupling between the hands and thereby form a task-dependent bimanual synergy for controlling the stochastic coupled movements as an entity.     

A simulation study of the degrees of freedom of movement in reaching and grasping

The question of independently controlled components in the act of reaching and grasping has attracted interest experimentally and theoretically. Data from 35 studies were recently found consistent with simulated kinematic finger and thumb trajectories optimised for minimum jerk. The present study closely reproduces those trajectories using a discrete-time model based on minimum acceleration. That model was further used to generate two-dimensional trajectories for finger and thumb to reach and grasp an elliptical object with varying position and/or orientation. Orthogonalisation of these four trajectories revealed one degree of freedom when direction of reach was constant and two degrees of freedom when direction of reach varied, irrespective of object distance and orientation. These simulations indicate that reach and grasp movements contain redundancy that is removable by formation of task-dependent synergies. As skilled movement can be planned and executed in a low dimension workspace, control of these independent components lessens central workload.     

Bernstein’s levels of movement construction: A contemporary perspective

Explanation of how goal-directed movements are made manifest is the ultimate aim of the field classically referred to as “motor control”. Essential to the sought-after explanation is comprehension of the supporting functional architecture. Seven decades ago, the Russian physiologist and movement scientist Nikolai A. Bernstein proposed a hierarchical model to explain the construction of movements. In his model, the levels of the hierarchy share a common language (i.e., they are commensurate) and perform complementing functions to bring about dexterous movements. The science of the control and coordination of movement in the phylum Craniata has made considerable progress in the intervening seven decades. The contemporary body of knowledge about each of Bernstein’s hypothesized functional levels is both more detailed and more sophisticated. A natural consequence of this progress, however, is the relatively independent theoretical development of a given level from the other levels. In this essay, we revisit each level of Bernstein’s hierarchy from the joint perspectives of (a) the ecological approach to perception-action and (b) dynamical systems theory. We review a substantial and relevant body of literature produced in different areas of study that are accommodated by this ecological-dynamical version of Bernstein’s levels. Implications for the control and coordination of movement and the challenges to producing a unified theory are discussed.     

How to achieve synergy in group decision making: Lessons to be learned from the hidden profile paradigm

Based on over 25 years of research on hidden profiles and information sharing in groups, and particularly our own work in this area, we outline a general model of how groups can achieve better decisions in a hidden profile situation than their individual members would have been capable of (i.e., synergy). At its core the model defines intensity and bias as the two key parameters that have to be optimised with regard to both the discussion of information and the processing of information in order to ensure synergy in group decision making. We review the empirical literature on information sharing and group decision making in the hidden profile paradigm (with a particular focus on our own studies) to illustrate how group decision quality can be enhanced by increasing intensity and decreasing bias in the discussion and processing of information. Finally we also outline why we think that the lessons learned from research using the hidden profile paradigm can be generalised to group decision-making research in general, and how these lessons can stimulate studies in other fields of group decision-making and group performance research.     

A study of a bimanual synergy associated with holding an object

The task of supporting an object with one or two hands was used to test the applicability of the notion of synergy. Subjects sat with their dominant forearm supported up to the wrist while holding a cylindrical “cup” between their thumb and fingers. Force transducers recorded the grip force applied normal to the cup's side by the thumb and the force applied normal to the cup bottom. On different series, a supporting force was added to and released from the bottom of the cup by the subject's non-dominant hand or by the experimenter. As predicted, the results indicated feedforward adjustments of the grip force, and of the EMGs, and significant correlations between grip force and supporting force when they were produced by two hands of one person, and the lack of such closely tied changes when the two forces were produced by two different persons. In the latter case, different subjects could demonstrate grip force changes in different directions. The findings suggest that grip force adjustments represented peripheral patterns of a single central process (a single synergy) rather than being separately controlled focal and postural components of the action.PsycINFO classification: 2330     

Neuromechanical synergies in single-leg landing reveal changes in movement control

Our purpose was to examine changes in single-leg landing biomechanics and movement control following alterations in mechanical task demands via external load and landing height. We examined lower-extremity kinematic, kinetic, and electromyographic (EMG) adjustments, as well as changes in movement control from neuromechanical synergies using separate principal component analyses (PCA). Nineteen healthy volunteers (15M, 4F, age: 24.3 ± 4.9 y, mass: 78.5 ± 14.7 kg, height: 1.73 ± 0.08 m) were analyzed among 9 single-leg drop landing trials in each of 6 experimental conditions (3 load and 2 landing height) computed as percentages of subject bodyweight (BW, BW + 12.5%, BW + 25%) and height (H12.5% & H25%). Condition order was counterbalanced, including: 1.) BW·H12.5, 2.) BW + 12.5·H12.5, 3.) BW + 25·H12.5, 4.) BW·H25, 5.) BW + 12.5·H25, 6.) BW + 25·H25. Lower-extremity sagittal joint angles and moments (hip, knee, & ankle), vertical ground reaction force (GRFz), and electrical muscle activity (gluteus maximus, biceps femoris, vastus medialis, medial gastrocnemius, & tibialis anterior muscles), were analyzed in each trial. Biomechanical adjustments and neuromechanical synergies were assessed using PCA. Subjects reduced effective landing height through segmental configuration adjustments at ground contact, extending at the hip and ankle joints with greater load and landing height (p ⩽ 0.028 and p ⩽ 0.013, respectively), while using greater medial gastrocnemius pre-activation with greater load (p ⩽ 0.006). Dimension reduction was observed under greater mechanical task demands, compressing and restructuring synergies among patterns of muscle activation, applied loads, and segmental configurations. These results provide insight into movement control and potential injury mechanisms in landing activities.     

Learning a pointing task with a kinematically redundant limb: Emerging synergies and patterns of final position variability

The study tested a hypothesis that practice of arm pointing movement can lead to a reorganization of the joint coordination reflected in the emergence of several synergies based on the same set of joints. In particular, involvement of the wrist may represent a choice by the central nervous system and not be driven by the typical “freezing-to-freeing” sequence. The effects of practice on the kinematic patterns and variability of a “fast and accurate” pointing movement using a pointer were studied. An obstacle was placed between the initial position and the target to encourage a curvilinear trajectory and larger wrist involvement. Practice led to a decrease in variability indices accompanied by an increase in movement speed of the endpoint and of the elbow and the shoulder, but not of the wrist joint. Five out of six subjects decreased the peak-to-peak amplitude of wrist motion. Before practice, the variability along the line connecting the endpoint to the shoulder (extent) was similar to that in the direction orthogonal to this line. After practice, variability was reduced along the extent, but not along the orthogonal direction perpendicular to this line. Prior to practice, indices of variability of the endpoint were lower than those of the marker placed over the wrist; after practice, the endpoint showed higher variability indices than the wrist. We interpret the data as consequences of the emergence of two synergies: (a) Pointing with a non-redundant set of the elbow and shoulder joints; and (b) keeping wrist position constant. The former synergy is based on a structural unit involving the elbow and the shoulder, while the latter is based on a structural unit that includes all the major arm joints.     

跨文化协同增效研究的3种典型视角

随着经济全球化进程的加速,跨国公司日益重视运用多元文化来创造国际竞争优势。论文首先讨论了“跨文化协同增效”的内涵以及达成跨文化协同增效的标准,然后介绍了跨文化协同增效研究的3种典型视角：加拿大研究者Adler的研究视角、德国研究者Krewer的研究视角和印尼研究者Tjitra的研究视角。3种不同的视角体现出研究者自身文化的特点。前两种视角是从西方文化出发,认为必须创造“第三种文化”来达成跨文化协同增效,而后一种视角则是从东方文化出发,针对本国文化的独特性进行跨文化协同增效理论研究。最后在比较分析3种不同研究视角基础上,认为应借鉴国外学者的研究思路,针对独特的中国文化进行跨文化协同增效研究