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Mark L Latash - One of the best experts on this subject based on the ideXlab platform.
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adaptations to fatigue of a single digit violate the Principle of Superposition in a multi finger static prehension task
2013Co-Authors: Tarkeshwar Singh, Vladimir M Zatsiorsky, Mark L LatashAbstract:We investigated the effects of exercise-induced fatigue of a digit on the biomechanics of a static prehension task. The participants were divided into two groups. One group performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). We analyzed the prehensile action as being based on a two-level hierarchy. Our first hypothesis was that fatigue of the thumb would have stronger effects at the upper level (action shared between the thumb and all four fingers combined—virtual finger) and fatigue of the index finger would have stronger effects at the lower level of the hierarchy (action of the virtual finger shared among actual fingers). We also hypothesized that fatigue would cause a decrease in the normal force applied by the exercised digit and correspondingly lead to a decrease in the normal force applied by the opposing digit(s). Our third hypothesis was that fatigue would leave the tangential forces unaffected. Fatigue led to a significant drop in the normal force of both exercised and non-exercised (opposing) digits. The tangential forces of the exercised digits increased after fatigue. This led to a drop in the safety margin in the group-thumb, but not group-index. As such, the results supported the first two hypotheses but not the third hypothesis. Overall, the results suggested that fatigue triggered a chain reaction that involved both forces and moments of force produced by individual digits leading to a violation of the Principle of Superposition. The findings are interpreted within the framework of the referent configuration hypothesis.
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multi muscle synergies in a dual postural task evidence for the Principle of Superposition
2010Co-Authors: Miriam Klous, Alessander Dannadossantos, Mark L LatashAbstract:We used the framework of the uncontrolled manifold hypothesis to quantify multi-muscle synergies stabilizing the moment of force about the frontal axis (MY) and the shear force in the anterior–posterior direction (FX) during voluntary body sway performed by standing subjects. We tested a hypothesis whether the controller could stabilize both MY and FX at the same time when the task and the visual feedback was provided only on one of the variables (MY). Healthy young subjects performed voluntary body sway in the anterior–posterior direction while different loads were attached at the ankle level producing horizontal forces acting forward or backwards. Principal component analysis was used to identify three M-modes within the space of integrated indices of muscle activation. Variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect a selected performance variable (MY or FX) and the other that did. Under all loading conditions and for each performance variable, a higher value for the former variance component was found. We interpret these results as reflections of two multi-M-mode synergies stabilizing both FX and MY. The indices of synergies were modulated within the sway cycle; both performance variables were better stabilized when the body moved forward than when it moved backward. The results show that the controller can use a set of three elemental variables (M-modes) to stabilize two performance variables at the same time. No negative interference was seen between the synergy indices computed for the two performance variables supporting the Principle of Superposition with respect to multi-muscle postural control.
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adjustments of prehension synergies in response to self triggered and experimenter triggered load and torque perturbations
2006Co-Authors: Jae Kun Shim, Vladimir M Zatsiorsky, Jaebum Park, Mark L LatashAbstract:Humans are known to show anticipatory adjustments in the grip force prior to a self-generated or predictable action or perturbation applied to a hand-held object. We investigated whether humans can also adjust covariation of individual finger forces (multi-finger synergies) prior to self-triggered perturbations. To address this issue, we studied adjustments in multi-digit synergies associated with applied load/torque perturbations while the subjects held a customized handle steadily. The main hypothesis was that the subjects would be able to demonstrate the phenomenon of anticipatory covariation, that is changes in covariation patterns among digit forces and moments of force in anticipation of a perturbation, but only when the perturbation was triggered by the subjects themselves. Based on the Principle of Superposition (decoupled grasping force and resultant torque control), we also expected to see different adjustments in indices of multi-digit synergies stabilizing the total gripping force and the total moment of force. The task for the subjects (n = 8) was to return the initial handle position as quickly as possible after a perturbation, which consisted of removing one of three loads hanging from the handle. There were six experimental conditions: two types of perturbations (self-triggered and experimenter-triggered) by three positions of the load (left, center, and right). Three-dimensional forces and moments of force recorded from each digit contact were used for the analysis. Indices of covariation among digit forces and among moments of force, previously employed for studying motor synergies, were computed across trials. Positive values of the indices reflected negative covariations of individual digit forces and moments of force (their inter-compensatory changes) to stabilize the total force and moment acting on the handle. In steady-state conditions, subjects showed strong positive indices for both digit forces and digit moments. Under the self-triggered conditions, changes in the indices of digit force and moment covariation were seen about 150 ms prior to the perturbation, while such changes were observed only after the perturbation under the experimenter-triggered conditions. Immediately following a perturbation, the indices of force and moment covariation rapidly changed to negative revealing the lack of inter-compensation among the individual digit forces and moments. Later, both indices showed a recovery to positive values; the recovery was faster in the self-triggered conditions than in the experimenter-triggered ones. During the steady-state phase after the perturbation, the indices of force and moment covariation decreased and increased, respectively, as compared to their values during the steady-state phase prior to the perturbation. We conclude that humans are able to adjust multi-digit synergies involved in prehensile tasks in anticipation of a self-triggered perturbation. These conclusions speak against hypotheses on the organization of multi-element actions based on optimal control Principles. Different changes in the indices of force and moment covariation after a perturbation corroborate the Principle of Superposition. We discuss relations of anticipatory covariation to anticipatory postural adjustments.
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prehension synergies trial to trial variability and Principle of Superposition during static prehension in three dimensions
2005Co-Authors: Jae Kun Shim, Mark L Latash, Vladimir M ZatsiorskyAbstract:We performed three-dimensional analysis of the conjoint changes of digit forces during prehension (prehension synergies) and tested applicability of the Principle of Superposition to three-dimensio...
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the Principle of Superposition in human prehension
2004Co-Authors: Vladimir M Zatsiorsky, Mark L Latash, Fan Gao, Jae Kun ShimAbstract:The experimental evidence supports the validity of the Principle of Superposition for multi-finger prehension in humans. Forces and moments of individual digits are defined by two independent commands: “Grasp the object stronger/weaker to prevent slipping” and “Maintain the rotational equilibrium of the object”. The effects of the two commands are summed up.
Vladimir M Zatsiorsky - One of the best experts on this subject based on the ideXlab platform.
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adaptations to fatigue of a single digit violate the Principle of Superposition in a multi finger static prehension task
2013Co-Authors: Tarkeshwar Singh, Vladimir M Zatsiorsky, Mark L LatashAbstract:We investigated the effects of exercise-induced fatigue of a digit on the biomechanics of a static prehension task. The participants were divided into two groups. One group performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). We analyzed the prehensile action as being based on a two-level hierarchy. Our first hypothesis was that fatigue of the thumb would have stronger effects at the upper level (action shared between the thumb and all four fingers combined—virtual finger) and fatigue of the index finger would have stronger effects at the lower level of the hierarchy (action of the virtual finger shared among actual fingers). We also hypothesized that fatigue would cause a decrease in the normal force applied by the exercised digit and correspondingly lead to a decrease in the normal force applied by the opposing digit(s). Our third hypothesis was that fatigue would leave the tangential forces unaffected. Fatigue led to a significant drop in the normal force of both exercised and non-exercised (opposing) digits. The tangential forces of the exercised digits increased after fatigue. This led to a drop in the safety margin in the group-thumb, but not group-index. As such, the results supported the first two hypotheses but not the third hypothesis. Overall, the results suggested that fatigue triggered a chain reaction that involved both forces and moments of force produced by individual digits leading to a violation of the Principle of Superposition. The findings are interpreted within the framework of the referent configuration hypothesis.
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adjustments of prehension synergies in response to self triggered and experimenter triggered load and torque perturbations
2006Co-Authors: Jae Kun Shim, Vladimir M Zatsiorsky, Jaebum Park, Mark L LatashAbstract:Humans are known to show anticipatory adjustments in the grip force prior to a self-generated or predictable action or perturbation applied to a hand-held object. We investigated whether humans can also adjust covariation of individual finger forces (multi-finger synergies) prior to self-triggered perturbations. To address this issue, we studied adjustments in multi-digit synergies associated with applied load/torque perturbations while the subjects held a customized handle steadily. The main hypothesis was that the subjects would be able to demonstrate the phenomenon of anticipatory covariation, that is changes in covariation patterns among digit forces and moments of force in anticipation of a perturbation, but only when the perturbation was triggered by the subjects themselves. Based on the Principle of Superposition (decoupled grasping force and resultant torque control), we also expected to see different adjustments in indices of multi-digit synergies stabilizing the total gripping force and the total moment of force. The task for the subjects (n = 8) was to return the initial handle position as quickly as possible after a perturbation, which consisted of removing one of three loads hanging from the handle. There were six experimental conditions: two types of perturbations (self-triggered and experimenter-triggered) by three positions of the load (left, center, and right). Three-dimensional forces and moments of force recorded from each digit contact were used for the analysis. Indices of covariation among digit forces and among moments of force, previously employed for studying motor synergies, were computed across trials. Positive values of the indices reflected negative covariations of individual digit forces and moments of force (their inter-compensatory changes) to stabilize the total force and moment acting on the handle. In steady-state conditions, subjects showed strong positive indices for both digit forces and digit moments. Under the self-triggered conditions, changes in the indices of digit force and moment covariation were seen about 150 ms prior to the perturbation, while such changes were observed only after the perturbation under the experimenter-triggered conditions. Immediately following a perturbation, the indices of force and moment covariation rapidly changed to negative revealing the lack of inter-compensation among the individual digit forces and moments. Later, both indices showed a recovery to positive values; the recovery was faster in the self-triggered conditions than in the experimenter-triggered ones. During the steady-state phase after the perturbation, the indices of force and moment covariation decreased and increased, respectively, as compared to their values during the steady-state phase prior to the perturbation. We conclude that humans are able to adjust multi-digit synergies involved in prehensile tasks in anticipation of a self-triggered perturbation. These conclusions speak against hypotheses on the organization of multi-element actions based on optimal control Principles. Different changes in the indices of force and moment covariation after a perturbation corroborate the Principle of Superposition. We discuss relations of anticipatory covariation to anticipatory postural adjustments.
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prehension synergies trial to trial variability and Principle of Superposition during static prehension in three dimensions
2005Co-Authors: Jae Kun Shim, Mark L Latash, Vladimir M ZatsiorskyAbstract:We performed three-dimensional analysis of the conjoint changes of digit forces during prehension (prehension synergies) and tested applicability of the Principle of Superposition to three-dimensio...
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the Principle of Superposition in human prehension
2004Co-Authors: Vladimir M Zatsiorsky, Mark L Latash, Fan Gao, Jae Kun ShimAbstract:The experimental evidence supports the validity of the Principle of Superposition for multi-finger prehension in humans. Forces and moments of individual digits are defined by two independent commands: “Grasp the object stronger/weaker to prevent slipping” and “Maintain the rotational equilibrium of the object”. The effects of the two commands are summed up.
Jae Kun Shim - One of the best experts on this subject based on the ideXlab platform.
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prehension synergies Principle of Superposition and hierarchical organization in circular object prehension
2007Co-Authors: Jae Kun Shim, Jaebum ParkAbstract:This study tests the following hypotheses in multi-digit circular object prehension: the Principle of Superposition (i.e., a complex action can be decomposed into independently controlled sub-actions) and the hierarchical organization (i.e., individual fingers at the lower level are coordinated to generate a desired task-specific outcome of the virtual finger at the higher level). Subjects performed 25 trials while statically holding a circular handle instrumented with five six-component force/moment sensors under seven external torque conditions. We performed a principal component (PC) analysis on forces and moments of the thumb and virtual finger (VF: an imagined finger producing the same mechanical effects of all finger forces and moments combined) to test the applicability of the Principle of Superposition in a circular object prehension. The synergy indices, measuring synergic actions of the individual finger (IF) moments for the stabilization of the VF moment, were calculated to test the hierarchical organization. Mixed-effect ANOVAs were used to test the dependent variable differences for different external torque conditions and different fingers at the VF and IF levels. The PC analysis showed that the elemental variables were decoupled into two groups: one group related to grasping stability control (normal force control) and the other group associated with rotational equilibrium control (tangential force control), which supports the Principle of Superposition. The synergy indices were always positive, suggesting error compensations between IF moments for the VF moment stabilization, which confirms the hierarchical organization of multi-digit prehension.
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adjustments of prehension synergies in response to self triggered and experimenter triggered load and torque perturbations
2006Co-Authors: Jae Kun Shim, Vladimir M Zatsiorsky, Jaebum Park, Mark L LatashAbstract:Humans are known to show anticipatory adjustments in the grip force prior to a self-generated or predictable action or perturbation applied to a hand-held object. We investigated whether humans can also adjust covariation of individual finger forces (multi-finger synergies) prior to self-triggered perturbations. To address this issue, we studied adjustments in multi-digit synergies associated with applied load/torque perturbations while the subjects held a customized handle steadily. The main hypothesis was that the subjects would be able to demonstrate the phenomenon of anticipatory covariation, that is changes in covariation patterns among digit forces and moments of force in anticipation of a perturbation, but only when the perturbation was triggered by the subjects themselves. Based on the Principle of Superposition (decoupled grasping force and resultant torque control), we also expected to see different adjustments in indices of multi-digit synergies stabilizing the total gripping force and the total moment of force. The task for the subjects (n = 8) was to return the initial handle position as quickly as possible after a perturbation, which consisted of removing one of three loads hanging from the handle. There were six experimental conditions: two types of perturbations (self-triggered and experimenter-triggered) by three positions of the load (left, center, and right). Three-dimensional forces and moments of force recorded from each digit contact were used for the analysis. Indices of covariation among digit forces and among moments of force, previously employed for studying motor synergies, were computed across trials. Positive values of the indices reflected negative covariations of individual digit forces and moments of force (their inter-compensatory changes) to stabilize the total force and moment acting on the handle. In steady-state conditions, subjects showed strong positive indices for both digit forces and digit moments. Under the self-triggered conditions, changes in the indices of digit force and moment covariation were seen about 150 ms prior to the perturbation, while such changes were observed only after the perturbation under the experimenter-triggered conditions. Immediately following a perturbation, the indices of force and moment covariation rapidly changed to negative revealing the lack of inter-compensation among the individual digit forces and moments. Later, both indices showed a recovery to positive values; the recovery was faster in the self-triggered conditions than in the experimenter-triggered ones. During the steady-state phase after the perturbation, the indices of force and moment covariation decreased and increased, respectively, as compared to their values during the steady-state phase prior to the perturbation. We conclude that humans are able to adjust multi-digit synergies involved in prehensile tasks in anticipation of a self-triggered perturbation. These conclusions speak against hypotheses on the organization of multi-element actions based on optimal control Principles. Different changes in the indices of force and moment covariation after a perturbation corroborate the Principle of Superposition. We discuss relations of anticipatory covariation to anticipatory postural adjustments.
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prehension synergies trial to trial variability and Principle of Superposition during static prehension in three dimensions
2005Co-Authors: Jae Kun Shim, Mark L Latash, Vladimir M ZatsiorskyAbstract:We performed three-dimensional analysis of the conjoint changes of digit forces during prehension (prehension synergies) and tested applicability of the Principle of Superposition to three-dimensio...
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the Principle of Superposition in human prehension
2004Co-Authors: Vladimir M Zatsiorsky, Mark L Latash, Fan Gao, Jae Kun ShimAbstract:The experimental evidence supports the validity of the Principle of Superposition for multi-finger prehension in humans. Forces and moments of individual digits are defined by two independent commands: “Grasp the object stronger/weaker to prevent slipping” and “Maintain the rotational equilibrium of the object”. The effects of the two commands are summed up.
Raymond W Yeung - One of the best experts on this subject based on the ideXlab platform.
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multilevel diversity coding with distortion
1995Co-Authors: Raymond W YeungAbstract:In a Diversity Coding System, an information source is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. We study a diversity coding problem in which there are two levels of decoders. The reconstructions of the source by decoders within the same level are identical, and are subject to the same distortion criterion. Our results imply a Principle of Superposition when the source consists of two independent data streams. Practical codes achieving zero error can easily be constructed for this special case. A class of open problems on this topic is also suggested. >
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multilevel diversity coding with distortion
1995Co-Authors: Raymond W YeungAbstract:In a Diversity Coding System, an information source is is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. In this paper, we study a diversity coding problem in which there are two levels of decoders. The reconstructions of the source by decoders within the same level are identical, and are subject to the same distortion criterion. Our results imply a Principle of Superposition when the source consists of two independent data streams. Practical codes achieving zero error can easily be constructed for this special case. A class of open problems on this topic is also suggested
Tarkeshwar Singh - One of the best experts on this subject based on the ideXlab platform.
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adaptations to fatigue of a single digit violate the Principle of Superposition in a multi finger static prehension task
2013Co-Authors: Tarkeshwar Singh, Vladimir M Zatsiorsky, Mark L LatashAbstract:We investigated the effects of exercise-induced fatigue of a digit on the biomechanics of a static prehension task. The participants were divided into two groups. One group performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). We analyzed the prehensile action as being based on a two-level hierarchy. Our first hypothesis was that fatigue of the thumb would have stronger effects at the upper level (action shared between the thumb and all four fingers combined—virtual finger) and fatigue of the index finger would have stronger effects at the lower level of the hierarchy (action of the virtual finger shared among actual fingers). We also hypothesized that fatigue would cause a decrease in the normal force applied by the exercised digit and correspondingly lead to a decrease in the normal force applied by the opposing digit(s). Our third hypothesis was that fatigue would leave the tangential forces unaffected. Fatigue led to a significant drop in the normal force of both exercised and non-exercised (opposing) digits. The tangential forces of the exercised digits increased after fatigue. This led to a drop in the safety margin in the group-thumb, but not group-index. As such, the results supported the first two hypotheses but not the third hypothesis. Overall, the results suggested that fatigue triggered a chain reaction that involved both forces and moments of force produced by individual digits leading to a violation of the Principle of Superposition. The findings are interpreted within the framework of the referent configuration hypothesis.