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| Record Number | 10241 |
| Reference Type | Conference Proceedings |
| Author(s) | Mistry, M.;Theodorou, E.;Liaw, G.;Yoshioka, T.;Schaal, S.;Kawato, M. |
| Year | 2008 |
| Title | An investigation of optimality in reaching movements with an acceleration based force field |
| Journal/Conference/Book Title | Abstracts of the Society of Neuroscience Meeting (SFN 2008) |
| Keywords | computational motor control, motor planning, optimization, force fields |
Abstract |
In this study, we ask how subjects respond to a force perturbation during a point to point reaching movement that first pushes the hand in one direction (orthogonal to the target direction) and then subsequently in the opposite direction, such that if no correction is made, the target will still be reached (albeit with a non-straight trajectory). We ask whether subjects choose to maintain a straight trajectory to the target by resisting the extraneous perturbation, or rather yield to execute a curved trajectory that requires less effort. For this experiment, we use the ATR PFM planar manipulandum to apply a force field that exerts a force at the subject's hand, perpendicular to the target direction and proportional to hand acceleration in the target direction. Thus if subjects execute a movement with a symmetric bell shaped velocity profile, as they would in the absence of a force field, the hand will first be perturbed to the right during the acceleration phase and then to the left by an equivalent magnitude during deceleration, and the hand will arrive at the target without additional correction. To determine if vision plays a role in subjects' control strategy, one group is given full visual feedback of the hand position throughout the movement, while another group is given only the hand position at the end of each trial. We compare the behavioral outcome with those predicted by a stochastic optimal controller implemented with both linear and nonlinear plants. Our behavioral results suggest that regardless of visual feedback, subjects have an initial preference for maintaining a straight hand trajectory over adopting a curved trajectory that requires reduced control effort. Although some subjects were able to successfully reach the target with curved trajectories during initial force field exposure, all subjects still adapted to a straight trajectory in subsequent trials. Evidence of significantly curved after effects after learning suggest that the adaptation occurs by an active prediction and compensation of force field dynamics, as opposed to a disturbance rejection via higher co-contraction or stiffness levels. We found these behavioral results to be inconsistent with some of the predictions made by stochastic optimal control.
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| Notes | clmc |
| Place Published | Washington, DC 2008 |
| Short Title | An investigation of optimality in reaching movements with an acceleration based force field |
| Papers are available as Adobe PDF ".pdf" files. Adobe Reader is available for free for all computer platforms.
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Page last modified on August 10, 2006, at 06:47 PM
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