| Records |
| Author |
Frenkel-Toledo, S.; Yamanaka, J.; Friedman, J.; Feldman, A.G.; Levin, M.F. |
| Title |
Referent control of anticipatory grip force during reaching in stroke: an experimental and modeling study |
Type |
Journal Article |
| Year |
2019 |
Publication |
Experimental Brain Research |
Abbreviated Journal |
Exp Brain Res |
| Volume |
237 |
Issue |
7 |
Pages |
1655-1672 |
| Keywords |
Anticipatory grip force; Referent control; Stroke |
Abstract  |
To evaluate normal and impaired control of anticipatory grip force (GF) modulation, we compared GF production during horizontal arm movements in healthy and post-stroke subjects, and, based on a physiologically feasible dynamic model, determined referent control variables underlying the GF-arm motion coordination in each group. 63% of 13 healthy and 48% of 13 stroke subjects produced low sustained initial force (< 10 N) and increased GF prior to arm movement. Movement-related GF increases were higher during fast compared to self-paced arm extension movements only in the healthy group. Differences in the patterns of anticipatory GF increases before the arm movement onset between groups occurred during fast extension arm movement only. In the stroke group, longer delays between the onset of GF change and elbow motion were related to clinical upper limb deficits. Simulations showed that GFs could emerge from the difference between the actual and the referent hand aperture (Ra) specified by the CNS. Similarly, arm movement could result from changes in the referent elbow position (Re) and could be affected by the co-activation (C) command. A subgroup of stroke subjects, who increased GF before arm movement, could specify different patterns of the referent variables while reproducing the healthy typical pattern of GF-arm coordination. Stroke subjects, who increased GF after arm movement onset, also used different referent strategies than controls. Thus, altered anticipatory GF behavior in stroke subjects may be explained by deficits in referent control. |
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0014-4819 |
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PMID:30976821 |
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no |
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98 |
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| Author |
Awasthi, Bhuvanesh; Friedman, Jason; Williams, Mark A |
| Title |
Processing of low spatial frequency faces at periphery in choice reaching tasks |
Type |
Journal Article |
| Year |
2011 |
Publication |
Neuropsychologia |
Abbreviated Journal |
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| Volume |
49 |
Issue |
7 |
Pages |
2136-2141 |
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| Abstract |
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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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 |
| Abstract |
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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| 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 |
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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. |
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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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no |
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Penn State @ write.to.jason @ |
Serial |
16 |
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| Author |
Raveh, E.; Portnoy, S.; Friedman, J. |
| Title |
Adding vibrotactile feedback to a myoelectric-controlled hand improves performance when online visual feedback is disturbed |
Type |
Journal Article |
| Year |
2018 |
Publication |
Human Movement Science |
Abbreviated Journal |
Hum Mov Sci |
| Volume |
58 |
Issue |
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Pages |
32-40 |
| Keywords |
Myoelectric prostheses; Sensorimotor control; Upper limb amputation; Visual feedback |
| Abstract |
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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| Notes |
PMID:29353091 |
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no |
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88 |
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