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| Author | Friedman, Jason; Latash, Mark L.; Zatsiorsky, Vladimir M. | ||||
| Title | Prehension synergies: a study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object | Type | Journal Article | ||
| Year | 2009 | Publication | Experimental Brain Research | Abbreviated Journal | Exp Brain Res |
| Volume | 197 | Issue  |
1 | Pages | 1-13 |
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| Abstract | We examined how the digit forces adjust when a load force acting on a hand-held object continuously varies. The subjects were required to hold the handle still while a linearly increasing and then decreasing force was applied to the handle. The handle was constrained, such that it could only move up and down, and rotate about a horizontal axis. In addition, the moment arm of the thumb tangential force was 1.5 times the moment arm of the virtual finger (VF, an imagined finger with the mechanical action equal to that of the four fingers) force. Unlike the situation when there are equal moment arms, the experimental setup forced the subjects to choose between (a) sharing equally the increase in load force between the thumb and VF but generating a moment of tangential force, which had to be compensated by negatively co-varying the moment due to normal forces, or (b) sharing unequally the load force increase between the thumb and VF but preventing generation of a moment of tangential forces. We found that different subjects tended to use one of these two strategies. These findings suggest that the selection by the CNS of prehension synergies at the VF-thumb level with respect to the moment of force is non-obligatory and reflects individual subject preferences. This unequal sharing of the load by the tangential forces, in contrast to the previously observed equal sharing, suggests that the invariant feature of prehension may be a correlated increase in tangential forces rather than an equal increase. | ||||
| Address | Department of Kinesiology, The Pennsylvania State University, 39 Recreation Building, University Park, PA, 16802, USA, jason.friedman@psu.edu | ||||
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| Language | English | Summary Language | Original Title | ||
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| ISSN | 1432-1106 | ISBN | Medium | ||
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| Notes | PMID:19554319 | Approved | no | ||
| Call Number | Penn State @ write.to.jason @ | Serial | 16 | ||
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| Author | Latash, M.L., Friedman, J., Kim, S.W., Feldman, A.G., Zatsiorsky, V.M. | ||||
| Title | Prehension Synergies and Control with Referent Hand Configurations | Type | Journal Article | ||
| Year | 2010 | Publication | Experimental Brain Research | Abbreviated Journal | Exp Brain Res |
| Volume | 202 | Issue |
1 | Pages | 213-229 |
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| Abstract | We used the framework of the equilibrium-point hypothesis (in its updated form based on the notion of referent configuration) to investigate the multi-digit synergies at two levels of a hypothetical hierarchy involved in prehensile actions. Synergies were analyzed at the thumb-virtual finger level (virtual finger is an imaginary digit with the mechanical action equivalent to that of the four actual fingers) and at the individual finger level. The subjects performed very quick vertical movements of a handle into a target. A load could be attached off-center to provide a pronation or supination torque. In a few trials, the handle was unexpectedly fixed to the table and the digits slipped off the sensors. In such trials, the hand stopped at a higher vertical position and rotated into pronation or supination depending on the expected torque. The aperture showed non-monotonic changes with a large, fast decrease and further increase, ending up with a smaller distance between the thumb and the fingers as compared to unperturbed trials. Multi-digit synergies were quantified using indices of co-variation between digit forces and moments of force across unperturbed trials. Prior to the lifting action, high synergy indices were observed at the individual finger level while modest indices were observed at the thumb-virtual finger level. During the lifting action, the synergies at the individual finger level disappeared while the synergy indices became higher at the thumb-virtual finger level. The results support the basic premise that, within a given task, setting a referent configuration may be described with a few referent values of variables that influence the equilibrium state, to which the system is attracted. Moreover, the referent configuration hypothesis can help interpret the data related to the trade-off between synergies at different hierarchical levels. | ||||
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| Notes | Approved | no | |||
| Call Number | Penn State @ write.to.jason @ | Serial | 19 | ||
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| Author | Kapur, Shweta; Friedman, Jason; Zatsiorsky, Vladimir M.; Latash, Mark L. | ||||
| Title | Finger interaction in a three-dimensional pressing task | Type | Journal Article | ||
| Year | 2010 | Publication | Experimental Brain Research | Abbreviated Journal | |
| Volume | 203 | Issue |
1 | Pages | 101-118 |
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| Abstract | Accurate control of forces produced by the fingers is essential for performing object manipulation. This study examines the indices of finger interaction when accurate time profiles of force are produced in different directions, while using one of the fingers or all four fingers of the hand. We hypothesized that patterns of unintended force production among shear force components may involve features not observed in the earlier studies of vertical force production. In particular, we expected to see unintended forces generated by non-task fingers not in the direction on the instructed force but in the opposite direction as well as substantial force production in directions orthogonal to the instructed direction. We also tested a hypothesis that multi-finger synergies, quantified using the framework of the uncontrolled manifold hypothesis, will help reduce across-trials variance of both total force magnitude and direction. Young, healthy subjects were required to produce accurate ramps of force in five different directions by pressing on force sensors with the fingers of the right (dominant) hand. The index finger induced the smallest unintended forces in non-task fingers. The little finger showed the smallest unintended forces when it was a non-task finger. Task fingers showed substantial force production in directions orthogonal to the intended force direction. During four-finger tasks, individual force vectors typically pointed off the task direction, with these deviations nearly perfectly matched to produce a resultant force in the task direction. Multi-finger synergy indices reflected strong co-variation in the space of finger modes (commands to fingers) that reduced variability of the total force magnitude and direction across trials. The synergy indices increased in magnitude over the first 30% of the trial time and then stayed at a nearly constant level. The synergy index for stabilization of total force magnitude was higher for shear force components as compared to the downward pressing force component. The results suggest complex interactions between enslaving and synergic force adjustments, possibly reflecting the experience with everyday prehensile tasks. For the first time, the data document multi-finger synergies stabilizing both shear force magnitude and force vector direction. These synergies may play a major role in stabilizing the hand action during object manipulation. |
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| Notes | in press | Approved | no | ||
| Call Number | Penn State @ write.to.jason @ | Serial | 20 | ||
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| Author | Friedman, J.; Korman, M. | ||||
| Title | Observation of an expert model induces a skilled movement coordination pattern in a single session of intermittent practice | Type | Journal Article | ||
| Year | 2019 | Publication | Scientific Reports | Abbreviated Journal | Sci Rep |
| Volume | 9 | Issue |
1 | Pages | 4609 |
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| Abstract | We tested how observation of a skilled pattern of planar movements can assist in the learning of a new motor skill, which otherwise requires rigorous long-term practice to achieve fast and smooth performance. Sixty participants performed a sequence of planar hand movements on pre-test, acquisition, post-test and 24 h post-training blocks, under 1 of 4 conditions: an observation group (OG), a slowed observation group (SOG), a random motion control group (RMCG) and a double physical training control group (DPTCG). The OG and SOG observed an expert model's right hand performing the study task intermittently throughout acquisition, RMCG observed random dots movement instead of a model. Participants in the DPTCG received extra physical practice trials instead of the visually observed trials. Kinematic analysis revealed that only in conditions with observation of an expert model there was an instant robust improvement in motor planning of the task. This step-wise improvement was not only persistent in post-training retests but was also apparently implicit and subject to further incremental improvements in movement strategy over the period of 24 hours. The rapid change in motor strategy was accompanied by a transient within-session increase in spatial error for the observation groups, but this went away by 24 h post-training. We suggest that observation of hand movements of an expert model coaligned with self-produced movements during training can significantly condense the time-course of ecologically relevant drawing/writing skill mastery. | ||||
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| Language | English | Summary Language | Original Title | ||
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| ISSN | 2045-2322 | ISBN | Medium | ||
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| Notes | PMID:30872661 | Approved | no | ||
| Call Number | Serial | 94 | |||
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| Author | Zacks, O.; Friedman, J. | ||||
| Title | Analogies can speed up the motor learning process | Type | Journal Article | ||
| Year | 2020 | Publication | Scientific Reports | Abbreviated Journal | Sci Rep |
| Volume | 10 | Issue |
1 | Pages | 6932 |
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| Abstract | Analogies have been shown to improve motor learning in various tasks and settings. In this study we tested whether applying analogies can shorten the motor learning process and induce insight and skill improvement in tasks that usually demand many hours of practice. Kinematic measures were used to quantify participant's skill and learning dynamics. For this purpose, we used a drawing task, in which subjects drew lines to connect dots, and a mirror game, in which subjects tracked a moving stimulus. After establishing a baseline, subjects were given an analogy, explicit instructions or no further instruction. We compared their improvement in skill (quantified by coarticulation or smoothness), accuracy and movement duration. Subjects in the analogy and explicit groups improved their coarticulation in the target task, while significant differences were found in the mirror game only at a slow movement frequency between analogy and controls.We conclude that a verbal analogy can be a useful tool for rapidly changing motor kinematics and movement strategy in some circumstances, although in the tasks selected it did not produce better performance in most measurements than explicit guidance. Furthermore, we observed that different movement facets may improve independently from others, and may be selectively affected by verbal instructions. These results suggest an important role for the type of instruction in motor learning. | ||||
| Address | Dept. of Physical Therapy, Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel | ||||
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| Language | English | Summary Language | Original Title | ||
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| Series Volume | Series Issue | Edition | |||
| ISSN | 2045-2322 | ISBN | Medium | ||
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| Notes | PMID:32332826; PMCID:PMC7181737 | Approved | no | ||
| Call Number | Penn State @ write.to.jason @ | Serial | 105 | ||
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