| |
Records |
Links |
|
Author |
Friedman, Jason; SKM, Varadhan; Zatsiorsky, Vladimir M.; Latash, Mark L. |
|
| |
Title |
The sources of two components of variance: an example of multifinger cyclic force production tasks at different frequencies |
Type |
Journal Article |
| |
Year |
2009 |
Publication |
Experimental Brain Research |
Abbreviated Journal |
Exp Brain Res |
|
| |
Volume |
196 |
Issue |
2 |
Pages |
263-277 |
|
| |
Keywords |
|
|
| |
Abstract |
In a multifinger cyclic force production task, the finger force variance measured across trials can be decomposed into two components, one that affects the combined force output (“bad variance”) and one that does not (“good variance”). Previous studies have found similar time patterns of “bad variance” and force rate leading to an approximately linear relationship between them. Based on this finding and a recently developed model of multifinger force production, we expected the “bad variance” during cyclic force production to increase monotonically with the rate of force change, both within a cycle and across trials at different frequencies. Alternatively, “bad variance” could show a dependence on task frequency, not on actual force derivative values. Healthy subjects were required to produce cyclic force patterns to prescribed targets by pressing on unidimensional force sensors, at a frequency set by a metronome. The task was performed with only the index finger, and with all four fingers. In the task with all four fingers, the “good variance” increased approximately linearly with an increase in the force magnitude. The “bad variance” showed within-a-cycle modulation similar to that of the force rate. However, an increase in the frequency did not lead to an increase in the “bad variance” that could be expected based on the natural relationships between action frequency and the rate of force change modulation. The results have been interpreted in the framework of an earlier model of multifinger force production where “bad variance” is a result of variance of the timing parameter. The unexpected lack of modulation of the “bad variance” with frequency suggests a drop in variance of the timing parameter with increased frequency. This mechanism may serve to maintain a constant acceptable level of variance under different conditions. |
|
| |
Address |
Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA |
|
| |
Corporate Author |
|
Thesis |
|
|
| |
Publisher |
|
Place of Publication |
|
Editor |
|
|
| |
Language |
English |
Summary Language |
|
Original Title |
|
|
| |
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
|
| |
Series Volume |
|
Series Issue |
|
Edition |
|
|
| |
ISSN  |
1432-1106 |
ISBN |
|
Medium |
|
|
| |
Area |
|
Expedition |
|
Conference |
|
|
| |
Notes |
PMID:19468721 |
Approved |
no |
|
| |
Call Number |
Penn State @ write.to.jason @ |
Serial |
15 |
|
| Permanent link to this record |
| |
|
| |
|
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 |
|
| |
Keywords |
|
|
| |
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 |
|
| |
Corporate Author |
|
Thesis |
|
|
| |
Publisher |
|
Place of Publication |
|
Editor |
|
|
| |
Language |
English |
Summary Language |
|
Original Title |
|
|
| |
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
|
| |
Series Volume |
|
Series Issue |
|
Edition |
|
|
| |
ISSN |
1432-1106 |
ISBN |
|
Medium |
|
|
| |
Area |
|
Expedition |
|
Conference |
|
|
| |
Notes |
PMID:19554319 |
Approved |
no |
|
| |
Call Number |
Penn State @ write.to.jason @ |
Serial |
16 |
|
| Permanent link to this record |
| |
|
| |
|
Author |
Friedman, Jason; Flash, Tamar |
|
| |
Title |
Trajectory of the index finger during grasping |
Type |
Journal Article |
| |
Year |
2009 |
Publication |
Experimental Brain Research |
Abbreviated Journal |
Exp Brain Res |
|
| |
Volume |
196 |
Issue |
4 |
Pages |
497-509 |
|
| |
Keywords |
|
|
| |
Abstract |
The trajectory of the index finger during grasping movements was compared to the trajectories predicted by three optimization-based models. The three models consisted of minimizing the integral of the weighted squared joint derivatives along the path (inertia-like cost), minimizing torque change, and minimizing angular jerk. Of the three models, it was observed that the path of the fingertip and the joint trajectories, were best described by the minimum angular jerk model. This model, which does not take into account the dynamics of the finger, performed equally well when the inertia of the finger was altered by adding a 20 g weight to the medial phalange. Thus, for the finger, it appears that trajectories are planned based primarily on kinematic considerations at a joint level. |
|
| |
Address |
Department of Computer Science and Applied Mathematics, Weizmann Institute of Science, Rehovot, Israel, write.to.jason@gmail.com |
|
| |
Corporate Author |
|
Thesis |
|
|
| |
Publisher |
|
Place of Publication |
|
Editor |
|
|
| |
Language |
English |
Summary Language |
|
Original Title |
|
|
| |
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
|
| |
Series Volume |
|
Series Issue |
|
Edition |
|
|
| |
ISSN |
1432-1106 |
ISBN |
|
Medium |
|
|
| |
Area |
|
Expedition |
|
Conference |
|
|
| |
Notes |
PMID:19521692 |
Approved |
no |
|
| |
Call Number |
Penn State @ write.to.jason @ |
Serial |
17 |
|
| Permanent link to this record |
| |
|
| |
|
Author |
Liebermann, D.G.; Defrin, R. |
|
| |
Title |
Characteristics of the nociceptive withdrawal response elicited under aware and unaware conditions |
Type |
Journal Article |
| |
Year |
2009 |
Publication |
Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology |
Abbreviated Journal |
J Electromyogr Kinesiol |
|
| |
Volume |
19 |
Issue |
2 |
Pages |
e114-22 |
|
| |
Keywords |
Adult; Arm/*physiopathology; Attention; *Awareness; Cues; Female; Humans; Male; Movement; *Muscle Contraction; Muscle, Skeletal/*physiopathology; Pain/*physiopathology; *Reflex; *Startle Reaction |
|
| |
Abstract |
BACKGROUND: Nociceptive withdrawal reflexes (NWR) are subject to supraspinal modulation. Therefore, awareness about a noxious stimulation may affect its characteristics. The goal of this study was to investigate the effect of different degrees of awareness on the NWR. METHOD: Eight subjects performed back and forth hand movements from a common starting point towards four visual targets during which NWR was evoked when subjects were either unaware or aware of a noxious stimulation (unaware-NWR and aware-NWR). For the comparison between the NWR under both conditions, onset latencies and kinematic variables were computed respectively from the recorded Biceps Brachii EMG and from the spatial coordinates of hand reflective markers. RESULTS: The onset latency of unaware-NWR (mean+/-SD 73.9+/-13 ms) was significantly shorter than that of the aware-NWR (91.1+/-27 ms, p<0.05). The total duration of the muscular activation was shorter in unaware-NWR than in aware-NWR. The slopes of the tangential velocity-time curves were steeper for unaware-NWR than for aware-NWR (p=0.057). CONCLUSIONS: The results suggest that supraspinal regulation of NWR under different degrees of awareness involves the re-parameterization of selected spatiotemporal aspects of a pre-structured motor response. |
|
| |
Address |
Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel-Aviv University, Ramat Aviv, Tel Aviv 69978, Israel |
|
| |
Corporate Author |
|
Thesis |
|
|
| |
Publisher |
|
Place of Publication |
|
Editor |
|
|
| |
Language |
English |
Summary Language |
|
Original Title |
|
|
| |
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
|
| |
Series Volume |
|
Series Issue |
|
Edition |
|
|
| |
ISSN |
1050-6411 |
ISBN |
|
Medium |
|
|
| |
Area |
|
Expedition |
|
Conference |
|
|
| |
Notes |
PMID:18063387 |
Approved |
no |
|
| |
Call Number |
|
Serial |
34 |
|
| Permanent link to this record |
| |
|
| |
|
Author |
Liebermann, D.G.; Berman, S.; Weingarden H.; Levin, M.F.; Weiss, P.L. |
|
| |
Title |
Kinematic features of arm and trunk movements in stroke patients and age-matched healthy controls during reaching in virtual and physical environments |
Type |
Conference Article |
| |
Year |
2009 |
Publication |
Virtual Rehabilitation International Conference |
Abbreviated Journal |
|
|
| |
Volume |
|
Issue |
|
Pages |
179-184 |
|
| |
Keywords |
|
|
| |
Abstract |
Motor performance of stroke patients and healthy individuals was compared in terms of selected kinematic features of arm and trunk movements while subjects reached for visual targets in virtual (VR) and physical (PH) environments. In PH, the targets were placed at an extended arm distance, while in VR comparably placed virtual targets were presented via GestureTek's IREX system. Our goal was to obtain further insights into research methods related to VR-based rehabilitation. Eight right-hemiparetic stroke patients (age =46-87 years) and 8 healthy adults (age =51-73 years) completed 84 reaching movements in VR and PH environments while seated. The results showed that arm and trunk movements differed in the two environments in patients and to a lesser extent in healthy individuals. Arm motion of patients became jerkier in VR, with larger paths and longer movement durations, and presented greater arm torsion (i.e., larger elbow rotations around the hand-shoulder axis). Interestingly, patients also showed a significant reduction of compensatory trunk movements during VR reaching. The findings indicate that when targets were perceived to be beyond hand reach, stroke patients may be less able to estimate 3D virtual target locations obtained from the 2D TV planar displays. This was not the case for healthy participants. |
|
| |
Address |
|
|
| |
Corporate Author |
|
Thesis |
|
|
| |
Publisher |
|
Place of Publication |
|
Editor |
|
|
| |
Language |
|
Summary Language |
|
Original Title |
|
|
| |
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
|
| |
Series Volume |
|
Series Issue |
|
Edition |
|
|
| |
ISSN |
|
ISBN |
|
Medium |
|
|
| |
Area |
|
Expedition |
|
Conference |
|
|
| |
Notes |
|
Approved |
no |
|
| |
Call Number |
|
Serial |
52 |
|
| Permanent link to this record |
