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| Author |
Friedman, J; Latash, M.L.; Zatsiorsky, V.M. |
| Title |
Directional variability of the isometric force vector produced by the hand in multi-joint planar tasks |
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Journal Article |
| Year |
2011 |
Publication |
Journal of Motor Behavior |
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43 |
Issue |
6 |
Pages |
451-463 |
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Numerous studies have examined control of force magnitude, but relatively little research has considered force direction control. In this study, subjects applied isometric forces to a handle and we compared within-trial variability when producing force in different directions. The standard deviation (SD) of the force parallel to the prescribed direction of force production increased linearly with the targeted force level, as did the SD of the force perpendicular to the instructed direction. In contrast, the SD of the angle of force production decreased with increased force level. In the four (of eight) instructed force directions where the endpoint force was generated due to a joint torque in only one joint (either the shoulder or elbow) the principal component axes in force space were well aligned with the prescribed direction of force production. In the other directions, the variance was approximately equal along the two force axes. The variance explained by the first principal component was significantly larger in torque space compared to the force space, and mostly corresponded to positive correlation between the joint torques. Such coordinated changes suggest that the torque variability was mainly due to the variability of the common drive to the muscles serving two joints, although this statement needs to be supported by direct studies of muscle activation in the future. |
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Penn State @ write.to.jason @ |
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26 |
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Awasthi, Bhuvanesh; Friedman, Jason; Williams, Mark A |
| Title |
Reach Trajectories Reveal Delayed Processing of Low Spatial Frequency Faces in Developmental Prosopagnosia |
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Journal Article |
| Year |
2012 |
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Cognitive Neuroscience |
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3 |
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2 |
Pages |
120-130 |
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Developmental prosopagnosia (DP) is characterized by a selective deficit in face recognition despite normal cognitive and neurological functioning. Previous research has established configural processing deficits in DP subjects. Low spatial frequency (LSF) information subserves configural face processing. Using hybrid stimuli, here we examined the evolution of perceptual dynamics and integration of LSF information by DP subjects while they pointed to high spatial frequency (HSF) face targets. Permutation analysis revealed a 230-ms delay in LSF processing by DP subjects as compared to controls. This delayed processing is likely to contribute to the difficulties associated with face recognition in DP subjects and is reflective of their alleged reliance on local rather than global features in face perception. These results suggest that quick and efficient processing of LSF information is critical for the development of normal face perception. |
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Penn State @ write.to.jason @ |
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27 |
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Liebermann, D.G.; Berman, S.; Weiss, P.L.T.; Levin, M.F. |
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Kinematics of reaching movements in a 2-d virtual environment in adults with and without stroke |
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Journal Article |
| Year |
2012 |
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IEEE Transactions on Neural Systems and Rehabilitation Engineering : a Publication of the IEEE Engineering in Medicine and Biology Society |
Abbreviated Journal |
IEEE Trans Neural Syst Rehabil Eng |
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20 |
Issue |
6 |
Pages |
778-787 |
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Virtual reality environments are increasingly being used for upper limb rehabilitation in poststroke patients. Our goal was to determine if arm reaching movements made in a 2-D video-capture virtual reality environment are similar to those made in a comparable physical environment. We compared arm and trunk kinematics for reaches made with the right, dominant arm to three targets (14 trials per target) in both environments by 16 adults with right poststroke hemiparesis and by eight healthy age-matched controls. Movement kinematics were recorded with a three-camera optoelectronic system at 100 samples/s. Reaching movements made by both control and stroke subjects were affected by viewing the targets in the video-capture 2-D virtual environment. Movements were slower, shorter, less straight, less accurate and involved smaller ranges of shoulder and elbow joint excursions for target reaches in the virtual environment compared to the physical environment in all subjects. Thus, there was a decrease in the overall movement quality for movements made in the 2-D virtual environment. This suggests that 2-D video-capture virtual reality environments should be used with caution when the goal of the rehabilitation program is to improve the quality of movement patterns of the upper limb. |
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1534-4320 |
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PMID:22907972 |
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28 |
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Biess, A.; Flash, T.; Liebermann, D.G. |
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Riemannian geometric approach to human arm dynamics, movement optimization, and invariance |
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Journal Article |
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2011 |
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Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics |
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Phys Rev E Stat Nonlin Soft Matter Phys |
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83 |
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3 Pt 1 |
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031927 |
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Arm/*physiology; Biomechanics; Computer Simulation; Humans; Kinetics; Male; Models, Biological; Models, Statistical; Models, Theoretical; *Movement; Psychomotor Performance/*physiology; Range of Motion, Articular/physiology; Reaction Time/physiology; Space Perception/*physiology; Torque |
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We present a generally covariant formulation of human arm dynamics and optimization principles in Riemannian configuration space. We extend the one-parameter family of mean-squared-derivative (MSD) cost functionals from Euclidean to Riemannian space, and we show that they are mathematically identical to the corresponding dynamic costs when formulated in a Riemannian space equipped with the kinetic energy metric. In particular, we derive the equivalence of the minimum-jerk and minimum-torque change models in this metric space. Solutions of the one-parameter family of MSD variational problems in Riemannian space are given by (reparameterized) geodesic paths, which correspond to movements with least muscular effort. Finally, movement invariants are derived from symmetries of the Riemannian manifold. We argue that the geometrical structure imposed on the arm's configuration space may provide insights into the emerging properties of the movements generated by the motor system. |
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Bernstein Center for Computational Neuroscience, DE-37073 Gottingen, Germany. armin@nld.ds.mpg.de |
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1539-3755 |
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PMID:21517543 |
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29 |
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Liebermann, D.G.; Levin, M.F.; McIntyre, J.; Weiss, P.L.; Berman, S. |
| Title |
Arm path fragmentation and spatiotemporal features of hand reaching in healthy subjects and stroke patients |
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Journal Article |
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2010 |
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Conference Proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference |
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Conf Proc IEEE Eng Med Biol Soc |
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2010 |
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5242-5245 |
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Aged; Aged, 80 and over; Analysis of Variance; Arm/*physiology; Biomechanics/physiology; Female; Hand/*physiology; *Health; Humans; Male; Middle Aged; Movement/*physiology; Posture/physiology; Principal Component Analysis; Stroke/*physiopathology; Time Factors |
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Arm motion in healthy humans is characterized by smooth and relatively short paths. The current study focused on 3D reaching in stroke patients. Sixteen right-hemiparetic stroke patients and 8 healthy adults performed 42 reaching movements towards 3 visual targets located at an extended arm distance. Performance was assessed in terms of spatial and temporal features of the movement; i.e., hand path, arm posture and smoothness. Differences between groups and within subjects were hypothesized for spatial and temporal aspects of reaching under the assumption that both are independent. As expected, upper limb motion of patients was characterized by longer and jerkier hand paths and slower speeds. Assessment of the number of sub-movements within each movement did not clearly discriminate between groups. Principal component analyses revealed specific clusters of either spatial or temporal measures, which accounted for a large proportion of the variance in patients but not in healthy controls. These findings support the notion of a separation between spatial and temporal features of movement. Stroke patients may fail to integrate the two aspects when executing reaching movements towards visual targets. |
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Physical Therapy Dept., Sackler Faculty of Medicine, Tel Aviv University, 69978 Israel. dlieberm@post.tau.ac.il |
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1557-170X |
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PMID:21096047 |
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30 |
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