| Records |
| 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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Penn State @ write.to.jason @ |
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19 |
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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 |
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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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2045-2322 |
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PMID:30872661 |
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no |
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94 |
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Raveh, E.; Portnoy, S.; Friedman, J. |
| Title |
Adding vibrotactile feedback to a myoelectric-controlled hand improves performance when online visual feedback is disturbed |
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Journal Article |
| Year |
2018 |
Publication |
Human Movement Science |
Abbreviated Journal |
Hum Mov Sci |
| Volume |
58 |
Issue |
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Pages |
32-40 |
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Myoelectric prostheses; Sensorimotor control; Upper limb amputation; Visual feedback |
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We investigated whether adding vibrotactile feedback to a myoelectric-controlled hand, when visual feedback is disturbed, can improve performance during a functional test. For this purpose, able-bodied subjects, activating a myoelectric-controlled hand attached to their right hand performed the modified Box & Blocks test, grasping and manipulating wooden blocks over a partition. This was performed in 3 conditions, using a repeated-measures design: in full light, in a dark room where visual feedback was disturbed and no auditory feedback – one time with the addition of tactile feedback provided during object grasping and manipulation, and one time without any tactile feedback. The average time needed to transfer one block was measured, and an infrared camera was used to give information on the number of grasping errors during performance of the test. Our results show that when vibrotactile feedback was provided, performance time was reduced significantly, compared with when no vibrotactile feedback was available. Furthermore, the accuracy of grasping and manipulation was improved, reflected by significantly fewer errors during test performance. In conclusion, adding vibrotactile feedback to a myoelectric-controlled hand has positive effects on functional performance when visual feedback is disturbed. This may have applications to current myoelectric-controlled hands, as adding tactile feedback may help prosthesis users to improve their functional ability during daily life activities in different environments, particularly when limited visual feedback is available or desirable. |
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Physical Therapy Department, Sackler Faculty of Medicine, Tel Aviv University, Israel. Electronic address: jason@post.tau.ac.il |
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0167-9457 |
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PMID:29353091 |
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no |
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88 |
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Zopf, R.; Friedman, J.; Williams, M.A. |
| Title |
The plausibility of visual information for hand ownership modulates multisensory synchrony perception |
Type |
Journal Article |
| Year |
2015 |
Publication |
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Abbreviated Journal |
Experimental Brain Research |
| Volume |
233 |
Issue |
8 |
Pages |
2311-2321 |
| Keywords |
Multisensory perception; Temporal synchrony perception; Virtual hand; Body representations; Body ownership; Sensory predictions |
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We are frequently changing the position of our bodies and body parts within complex environments. How does the brain keep track of one’s own body? Current models of body ownership state that visual body ownership cues such as viewed object form and orientation are combined with multisensory information to correctly identify one’s own body, estimate its current location and evoke an experience of body ownership. Within this framework, it may be possible that the brain relies on a separate perceptual analysis of body ownership cues (e.g. form, orientation, multisensory synchrony). Alternatively, these cues may interact in earlier stages of perceptual processing—visually derived body form and orientation cues may, for example, directly modulate temporal synchrony perception. The aim of the present study was to distinguish between these two alternatives. We employed a virtual hand set-up and psychophysical methods. In a two-interval force-choice task, participants were asked to detect temporal delays between executed index finger movements and observed movements. We found that body-specifying cues interact in perceptual processing. Specifically, we show that plausible visual information (both form and orientation) for one’s own body led to significantly better detection performance for small multisensory asynchronies compared to implausible visual information. We suggest that this perceptual modulation when visual information plausible for one’s own body is present is a consequence of body-specific sensory predictions. |
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Springer Berlin Heidelberg |
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0014-4819 |
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no |
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78 |
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Lowenthal-Raz, J.; Liebermann, D.G.; Friedman, J.; Soroker, N. |
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Kinematic descriptors of arm reaching movement are sensitive to hemisphere-specific immediate neuromodulatory effects of transcranial direct current stimulation post stroke |
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Journal Article |
| Year |
2024 |
Publication |
Scientific Reports |
Abbreviated Journal |
Sci Rep |
| Volume |
14 |
Issue |
1 |
Pages |
11971 |
| Keywords |
Humans; *Transcranial Direct Current Stimulation/methods; Male; Female; Middle Aged; *Stroke/physiopathology/therapy; Biomechanical Phenomena; Aged; *Arm/physiopathology; *Movement/physiology; *Stroke Rehabilitation/methods; Single-Blind Method; Cross-Over Studies |
| Abstract |
Transcranial direct current stimulation (tDCS) exerts beneficial effects on motor recovery after stroke, presumably by enhancement of adaptive neural plasticity. However, patients with extensive damage may experience null or deleterious effects with the predominant application mode of anodal (excitatory) stimulation of the damaged hemisphere. In such cases, excitatory stimulation of the non-damaged hemisphere might be considered. Here we asked whether tDCS exerts a measurable effect on movement quality of the hemiparetic upper limb, following just a single treatment session. Such effect may inform on the hemisphere that should be excited. Using a single-blinded crossover experimental design, stroke patients and healthy control subjects were assessed before and after anodal, cathodal and sham tDCS, each provided during a single session of reaching training (repeated point-to-point hand movement on an electronic tablet). Group comparisons of endpoint kinematics at baseline-number of peaks in the speed profile (NoP; smoothness), hand-path deviations from the straight line (SLD; accuracy) and movement time (MT; speed)-disclosed greater NoP, larger SLD and longer MT in the stroke group. NoP and MT revealed an advantage for anodal compared to sham stimulation of the lesioned hemisphere. NoP and MT improvements under anodal stimulation of the non-lesioned hemisphere correlated positively with the severity of hemiparesis. Damage to specific cortical regions and white-matter tracts was associated with lower kinematic gains from tDCS. The study shows that simple descriptors of movement kinematics of the hemiparetic upper limb are sensitive enough to demonstrate gain from neuromodulation by tDCS, following just a single session of reaching training. Moreover, the results show that tDCS-related gain is affected by the severity of baseline motor impairment, and by lesion topography. |
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Faculty of Medicine, Tel-Aviv University, Tel Aviv, Israel. nachum@soroker.online |
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2045-2322 |
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PMID:38796610; PMCID:PMC11127956 |
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no |
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125 |
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