Enslaving effects in multi-finger force production

Zatsiorsky, Vladimir M.; Li, Zong Ming; Latash, Mark L.

doi:10.1007/s002219900261

Cited by 375 publications

(353 citation statements)

References 25 publications

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“…In an earlier study, the magnitude of enslaving has been shown to be larger for fingers adjacent to the master finger than for "remote" slave fingers (Zatsiorsky et al 2000). This similarity suggests that finger proximity is an important factor defining both slave finger magnitude and direction.…”

Section: Enslaved Finger Forcesmentioning

confidence: 87%

“…to explore the dependence of the direction of forces produced by fingers that are not required to produce force (enslaved forces; Li et al 1998aLi et al , 1998bZatsiorsky et al 1998Zatsiorsky et al , 2000 on the target direction; and 4. to establish whether there is a multi-finger synergy stabilizing the direction of the total force.…”

Section: To Test the Dependence Of Direction Accuracy On Target Forcementioning

confidence: 99%

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Control of finger force direction in the flexion-extension plane

2004

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We have examined the interaction among individual finger forces in tasks that required the production of the total force by a subset of fingers in a particular direction in the flexion-extension plane. Nine subjects produced fingertip forces in a prescribed direction with a maximum voluntary contraction (MVC) effort and held the peak force for two seconds. Six finger combinations were tested, four single-finger tasks-Index (I), Middle (M), Ring (R) and Little (L)-one two-digit task (IM), and one four-digit task (IMRL). The subjects were asked to generate the finger forces in two directions, 0° (perpendicular to the surface of the transducer) and 15° toward the palm. In all task conditions, there were two experimental sessions, with and without visual feedback on the task force vector. The main findings were:1. The target direction significantly affected the constant error (CE) but not the variable error (VE) while removal of the feedback resulted in an increase in VE. 2.The direction of the forces produced by fingers that were not explicitly required to produce force (enslaved fingers) depended on the target direction. 3.In multi-finger tasks, the individual fingers produced force in directions that could differ significantly from the target direction, while the resultant force pointed in the target direction. There was a negative co-variation among the deviations of the directions of the individual finger forces from the target direction. If a finger force vector deviated from the target, another finger force vector was likely to deviate in the opposite direction. We conclude that a multi-finger synergy is involved in the control of the finger force direction.

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Section: Enslaved Finger Forcesmentioning

confidence: 87%

Section: To Test the Dependence Of Direction Accuracy On Target Forcementioning

confidence: 99%

Control of finger force direction in the flexion-extension plane

2004

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“…The hypothesis assumes that the controller organizes co-variation among elemental variables to stabilize a certain value of a performance variable (F TOT or M TOT in our study). Individual finger forces co-vary in a non-task-specific fashion because of the phenomenon of enslaving, i.e., unintended force production by fingers when other fingers of the hand produce force (Li et al 1998;Zatsiorsky et al 2000). Hence, the first step was to convert the data sets from time series of finger forces to time series of elemental variables, force modes that can be, at least hypothetically, modified by the controller one at a time.…”

Section: Ucm Analysismentioning

confidence: 99%

“…In particular, unintended force production (enslaving) is the smallest in the index finger and higher in the ring and little fingers (Li et al 1998;Zatsiorsky et al 2000;Lang and Schieber 2004). Note, however, that enslaving effects were taken into account in our analysis of multifinger synergies that used not finger forces but finger modes as elemental variables.…”

Section: Rotational Efforts Into Pronation and Supinationmentioning

confidence: 99%

Finger synergies during multi-finger cyclic production of moment of force

2006

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We investigated multi-finger synergies stabilizing the total moment of force and the total force when the subjects produced a quick cyclic change in the total moment of force. The seated subjects performed the task with the fingers of the dominant arm while paced by the metronome at 1.33 Hz. They were required to produce a rhythmic, sine-like change in the total pronation-supination moment of force computed with respect to the midpoint between the middle and ring fingers. The framework of the uncontrolled manifold hypothesis was used to compute indices of stabilization of the total moment and of the total force across 20 cycles. Variance of the total moment showed a cyclic pattern with peaks close to the peak rate of the moment change. Variance of the total force was maximal close to peak moment into supination. Higher magnitudes of the moment directed against the required moment direction (antagonist moment) were produced by individual fingers during supination efforts as compared to pronation efforts. Indices of multi-finger synergies showed across-trials stabilization of the total moment over the whole cycle but not of the total force. These indices were smaller during supination efforts. We conclude that the central nervous system facilitates multi-finger synergies stabilizing the total rotational action across a variety of tasks. Synergies stabilizing the total force are not seen in tasks that do not explicitly require accurate force control. Pronation efforts are performed more efficiently and with better stabilization of the action.

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“…No a priori hypotheses could be formulated with respect to these comparisons. However, differences could be expected based on earlier studies that have shown effects of hand dominance on indices of finger interaction , different ability to control finger forces independently across fingers (typically, the index finger is better controlled individually as compared to the other fingers Zatsiorsky et al 1998Zatsiorsky et al , 2000, and differences in bilateral effects in symmetrical and asymmetrical two-hand tasks (Li et al 2002). Most of the cited studies used maximal force production tasks; thus one cannot readily make predictions with respect to our task of accurate sub-maximal force production.…”

Section: Introductionmentioning

confidence: 99%

Hierarchies of synergies: an example of two-hand, multi-finger tasks

2006

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We explored the ability of the central nervous system (CNS) to assemble synergies stabilizing the output of sets of effectors at two levels of a control hierarchy. Specifically, we asked a question: can the CNS organize both two-hand and within-a-hand force stabilizing synergies in a simple two-hand force production task that involves two fingers per hand? Intuitively, one could expect a positive answer; that is, forces produced by each hand are expected to co-vary negatively across trials to bring down the total force variability, while forces produced by each finger within-a-hand are expected to co-vary negatively to reduce the variability of that hand's contribution to the total force. The subjects were instructed to follow a trapezoidal time profile with the signal corresponding to the force produced by a set of instructed fingers in one-hand tasks with two-finger force production and in two-hand tasks with involvement of both symmetrical and asymmetrical finger pairs in the two hands. Finger force co-variation across trials was quantified and used as an index of stabilization of the force produced by all the instructed fingers, and of the force produced by finger pairs within-a-hand. No major differences were seen between the dominant and the non-dominant hand and between the twohand tasks with symmetrical and asymmetrical finger involvement. Stronger synergies were seen in the index-middle finger pair as compared to the ring-little finger pair. The main result of the study is the significantly weaker or even lacking two-finger force stabilizing synergies within-a-hand during two-hand tasks while such synergies were present in one-hand tasks. This observation points at a potential limitation in the ability of the CNS to organize synergies at two levels of a control hierarchy simultaneously. It also allows suggesting a hypothesis on two types of synergies in the human motor repertoire, well-practiced synergies that form a library serving as the foundation for all novel actions, and freshly assembled synergies.

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Enslaving effects in multi-finger force production

Cited by 375 publications

References 25 publications

Control of finger force direction in the flexion-extension plane

Control of finger force direction in the flexion-extension plane

Finger synergies during multi-finger cyclic production of moment of force

Hierarchies of synergies: an example of two-hand, multi-finger tasks

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