Modeling constraints to redundancy in bimanual force coordination

Hu, Xiaogang; Newell, Karl M.

doi:10.1152/jn.01086.2010

Cited by 23 publications

(19 citation statements)

References 54 publications

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“…This could be done by adding constraints to the system (for example, self-imposed, intentional constraints, e.g. Hu and Newell 2011), or by using optimization approaches, i.e., looking for a solution from an infinite set that minimizes (or maximizes) a cost function. A number of cost functions have been explored (reviewed in Nelson 1984; Prilutsky and Zatsiorsky 2002), such as minimal time, minimal energy expenditure, minimal jerk, minimal fatigue, minimal discomfort, and many others.…”

Section: Discussionmentioning

confidence: 99%

Optimality and stability of intentional and unintentional actions: I. Origins of drifts in performance

et al. 2016

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We address the nature of unintentional changes in performance in two papers. This first paper tested a hypothesis that unintentional changes in performance variables during continuous tasks without visual feedback are due to two processes. First, there is a drift of the referent coordinate for the salient performance variable toward the actual coordinate of the effector. Second, there is a drift toward minimum of a cost function. We tested this hypothesis in four-finger isometric pressing tasks that required the accurate production of a combination of total moment and total force with natural and modified finger involvement. Subjects performed accurate force/moment production tasks under visual feedback, and then visual feedback was removed for some or all of the salient variables. Analytical inverse optimization was used to compute a cost function. Without visual feedback, both force and moment drifted slowly toward lower absolute magnitudes. Over 15 s, the force drop could reach 20% of its initial magnitude while moment drop could reach 30% of its initial magnitude. Individual finger forces could show drifts toward both higher and lower forces. The cost function estimated using the analytical inverse optimization reduced its value as a consequence of the drift. We interpret the results within the framework of hierarchical control with referent spatial coordinates for salient variables at each level of the hierarchy combined with synergic control of salient variables. The force drift is discussed as a natural relaxation process toward states with lower potential energy in the physical (physiological) system involved in the task.

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Section: Discussionmentioning

confidence: 99%

Optimality and stability of intentional and unintentional actions: I. Origins of drifts in performance

et al. 2016

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“…If the subject does not correct performance due to poor feedback resolution and/or low motivation, the former factor may be expected to lead to negative finger force co-variation. Several studies documented both effects (Ranganathan and Newell 2008a,b; Hu and Newell 2011a) and explored them theoretically (Hu and Newell 2011b). …”

Section: Discussionmentioning

confidence: 99%

Interpersonal synergies: static prehension tasks performed by two actors

Solnik

Reschechtko

et al. 2016

Exp Brain Res

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We investigated multi-digit synergies stabilizing components of the resultant force vector during joint performance of a static prehension task by two persons as compared to similar tasks performed by a single person using both hands. Subjects transferred the instrumented handle from the right hand to the left hand (one-person condition) or passed that handle to another person (two-person condition) while keeping the handle's position and orientation stationary. Only three digits were involved per hand, the thumb, the index finger, and the middle finger; the forces and moments produced by the digits were measured by six-component sensors. We estimated the performance stabilizing synergies within the uncontrolled manifold (UCM) framework by quantifying the inter-trial variance structure of digit forces and moments. The analysis was performed at three levels: between hands, between virtual finger and virtual thumb (imagined digits producing the same mechanical variables as the corresponding actual digits combined) produced by the two hands (in both interpersonal and intrapersonal conditions), and between the thumb and virtual finger for one hand only. Additionally, we performed correlation and phase synchronization analyses of resultant tangential forces and internal normal forces. Overall, the one-person conditions were characterized by higher amount of inter-trial variance that did not affect resultant normal force components, higher internal components of normal forces, and stronger synchronization of the normal forces generated by the hands. Our observations suggest that in two-person tasks, when participants try to achieve a common mechanical outcome, the performance stabilizing synergies depend on non-visual information exchange, possibly via the haptic and proprioceptive systems. Therefore, synergies quantified in tasks using visual feedback only may not be generalizable to more natural tasks.

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“…It does so by imposing (time-varying) constraints on the system “body+environment” (cf. Hu and Newell 2011) and allowing solutions to emerge given the actual state of this system (which never repeats exactly over repetitive trials). In other words, laws of physics define behavior of the neuromotor system at any level just like they define motion of Na + during the action potential generation.…”

Section: The Principle Of Abundancementioning

confidence: 99%

The bliss (not the problem) of motor abundance (not redundancy)

2012

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Motor control is an area of natural science exploring how the nervous system interacts with other body parts and the environment to produce purposeful, coordinated actions. A central problem of motor control – the problem of motor redundancy – was formulated by Nikolai Bernstein as the problem of elimination of redundant degrees-of-freedom. Traditionally, this problem has been addressed using optimization methods based on a variety of cost functions. This review draws attention to a body of recent findings suggesting that the problem has been formulated incorrectly. An alternative view has been suggested as the principle of abundance, which considers the apparently redundant degrees-of-freedom as useful and even vital for many aspects of motor behavior. Over the past ten years, dozens of publications have provided support for this view based on the ideas of synergic control, computational apparatus of the uncontrolled manifold hypothesis, and the equilibrium-point (referent configuration) hypothesis. In particular, large amounts of “good variance” – variance in the space of elements that has no effect on the overall performance – have been documented across a variety of natural actions. “Good variance” helps an abundant system to deal with secondary tasks and unexpected perturbations; its amount shows adaptive modulation across a variety of conditions. These data support the view that there is no problem of motor redundancy; there is bliss of motor abundance.

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Modeling constraints to redundancy in bimanual force coordination

Cited by 23 publications

References 54 publications

Optimality and stability of intentional and unintentional actions: I. Origins of drifts in performance

Optimality and stability of intentional and unintentional actions: I. Origins of drifts in performance

Interpersonal synergies: static prehension tasks performed by two actors

The bliss (not the problem) of motor abundance (not redundancy)

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