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Latash, M.L., Friedman, J., Kim, S.W., Feldman, A.G., Zatsiorsky, V.M. |
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Prehension Synergies and Control with Referent Hand Configurations |
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2010 |
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Experimental Brain Research |
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Exp Brain Res |
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202 |
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1 |
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213-229 |
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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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Friedman, Jason; Latash, Mark L.; Zatsiorsky, Vladimir M. |
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Prehension synergies: a study of digit force adjustments to the continuously varied load force exerted on a partially constrained hand-held object |
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2009 |
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Experimental Brain Research |
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Exp Brain Res |
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197 |
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1 |
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1-13 |
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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. |
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Department of Kinesiology, The Pennsylvania State University, 39 Recreation Building, University Park, PA, 16802, USA, jason.friedman@psu.edu |
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1432-1106 |
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PMID:19554319 |
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Penn State @ write.to.jason @ |
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16 |
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Awasthi, Bhuvanesh; Friedman, Jason; Williams, Mark A |
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Processing of low spatial frequency faces at periphery in choice reaching tasks |
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2011 |
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Neuropsychologia |
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49 |
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7 |
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2136-2141 |
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Various aspects of face processing have been associated with distinct ranges of spatial frequencies. Configural processing of faces depends chiefly on low spatial frequency (LSF) information whereas high spatial frequency (HSF) supports feature based processing. However, it has also been argued that face processing has a foveal-bias (HSF channels dominate the fovea). Here we used reach trajectories as a continuous behavioral measure to study perceptual processing of faces. Experimental stimuli were LSF–HSF hybrids of male and female faces superimposed and were presented peripherally and centrally. Subject reached out to touch a specified sex and their movements were recorded. The reaching trajectories reveal that there is less effect of (interference by) LSF faces at fovea as compared to periphery while reaching to HSF targets. These results demonstrate that peripherally presented LSF information, carried chiefly by magnocellular channels, enables efficient processing of faces, possibly via a retinotectal (subcortical) pathway. |
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24 |
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Steinhart, S.; Weiss, P.L.; Friedman, J. |
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Proximal and distal movement patterns during a graphomotor task in typically developing children and children with handwriting problems |
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2021 |
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Journal of Neuroengineering and Rehabilitation |
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J Neuroeng Rehabil |
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18 |
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1 |
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178 |
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Arm; Biomechanical Phenomena; Child; *Handwriting; Humans; Motor Skills; *Movement; Upper Extremity; Distal joints; Handwriting; Motor control; Movement analysis; Proximal; Stability |
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BACKGROUND: Therapists specializing in handwriting difficulties in children often address motor problems including both proximal and distal movements in the upper extremity. Kinematic measures can be used to investigate various aspects of handwriting. This study examined differences in movement patterns in proximal and distal joints of the upper extremity during graphomotor tasks between typically developing children with and without handwriting problems. Additionally, it explored relationships between movement patterns, speed, and legibility of writing. METHODS: Forty-one children, aged 7-11 years, were assessed with the Aleph Aleph Ktav Yad Hebrew Handwriting assessment and the Beery Test of Visual Motor Integration and, based on their scores, were divided into a research group (with handwriting difficulties) and a control group (without handwriting difficulties). Upper extremity joint movement patterns were analyzed with a motion capture system. Differences in the quality of shapes traced and copied on a graphics tablet positioned horizontally and vertically were compared. Between-group differences and relationships with speed and legibility were analyzed. RESULTS: In both groups, there was greater movement in the distal compared to the proximal joints, greater movement when performing the task in a horizontal compared to a vertical plane, and greater movement when tracing than copying. Joint movements in the arm executed scaled-down versions of the shapes being drawn. While the amount of joint displacement was similar between groups, children in the research group showed greater dissimilarity between the drawn shape and the shape produced by the proximal joints. Finally, the drawing measure on the tablet was a significant predictor of legibility, speed of writing, visual motor integration and motor coordination, whereas the dissimilarity measure of joint movement was a significant predictor of speed of writing and motor coordination. CONCLUSIONS: This study provides support for the role of the distal upper extremity joints in the writing process and some guidance to assist clinicians in devising treatment strategies for movement-related handwriting problems. While we observed differences in proximal joint movements between the children with and without handwriting difficulties, the extent to which they are responsible for the differences in drawing quality remains to be determined. Further studies should use a similar methodology to examine additional tasks such as drawing shapes of varying sizes. |
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Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel. jason@tau.ac.il |
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1743-0003 |
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PMID:34930334; PMCID:PMC8690895 |
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118 |
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Tamir-Ostrover, H.; Hassin-Baer, S.; Fay-Karmon, T.; Friedman, J. |
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Title |
Quantifying Changes in Dexterity as a Result of Piano Training in People with Parkinson's Disease |
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2024 |
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Sensors (Basel, Switzerland) |
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Sensors (Basel) |
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24 |
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11 |
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Humans; *Parkinson Disease/physiopathology; Pilot Projects; Male; Aged; Female; Quality of Life; Middle Aged; Motor Skills/physiology; Music; Surveys and Questionnaires; Activities of Daily Living; Fingers/physiology/physiopathology; Parkinson's disease; dexterity; force sensors; music; piano; sonification; training; uncontrolled manifold |
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People with Parkinson's disease often show deficits in dexterity, which, in turn, can lead to limitations in performing activities of daily life. Previous studies have suggested that training in playing the piano may improve or prevent a decline in dexterity in this population. In this pilot study, we tested three participants on a six-week, custom, piano-based training protocol, and quantified dexterity before and after the intervention using a sensor-enabled version of the nine-hole peg test, the box and block test, a test of finger synergies using unidimensional force sensors, and the Quantitative Digitography test using a digital piano, as well as selected relevant items from the motor parts of the MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and the Parkinson's Disease Questionnaire (PDQ-39) quality of life questionnaire. The participants showed improved dexterity following the training program in several of the measures used. This pilot study proposes measures that can track changes in dexterity as a result of practice in people with Parkinson's disease and describes a potential protocol that needs to be tested in a larger cohort. |
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Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 6997801, Israel |
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1424-8220 |
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PMID:38894110; PMCID:PMC11174779 |
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124 |
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