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Feedforward control strategies of subjects with transradial amputation in planar reaching  [PDF]
Anthony J. Metzger, MBE,Alexander W. Dromerick, MD,Christopher N. Schabowsky, MS,Rahsaan J. Holley, MS
Journal of Rehabilitation Research and Development , 2010,
Abstract: The rate of upper-limb amputations is increasing, and the rejection rate of prosthetic devices remains high. People with upper-limb amputation do not fully incorporate prosthetic devices into their activities of daily living. By understanding the reaching behaviors of prosthesis users, researchers can alter prosthetic devices and develop training protocols to improve the acceptance of prosthetic limbs. By observing the reaching characteristics of the nondisabled arms of people with amputation, we can begin to understand how the brain alters its motor commands after amputation. We asked subjects to perform rapid reaching movements to two targets with and without visual feedback. Subjects performed the tasks with both their prosthetic and nondisabled arms. We calculated endpoint error, trajectory error, and variability and compared them with those of nondisabled control subjects. We found no significant abnormalities in the prosthetic limb. However, we found an abnormal leftward trajectory error (in right arms) in the nondisabled arm of prosthetic users in the vision condition. In the no-vision condition, the nondisabled arm displayed abnormal leftward endpoint errors and abnormally higher endpoint variability. In the vision condition, peak velocity was lower and movement duration was longer in both arms of subjects with amputation. These abnormalities may reflect the cortical reorganization associated with limb loss.
The Effect of Sensory Uncertainty Due to Amblyopia (Lazy Eye) on the Planning and Execution of Visually-Guided 3D Reaching Movements  [PDF]
Ewa Niechwiej-Szwedo, Herbert C. Goltz, Manokaraananthan Chandrakumar, Agnes M. F. Wong
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0031075
Abstract: Background Impairment of spatiotemporal visual processing in amblyopia has been studied extensively, but its effects on visuomotor tasks have rarely been examined. Here, we investigate how visual deficits in amblyopia affect motor planning and online control of visually-guided, unconstrained reaching movements. Methods Thirteen patients with mild amblyopia, 13 with severe amblyopia and 13 visually-normal participants were recruited. Participants reached and touched a visual target during binocular and monocular viewing. Motor planning was assessed by examining spatial variability of the trajectory at 50–100 ms after movement onset. Online control was assessed by examining the endpoint variability and by calculating the coefficient of determination (R2) which correlates the spatial position of the limb during the movement to endpoint position. Results Patients with amblyopia had reduced precision of the motor plan in all viewing conditions as evidenced by increased variability of the reach early in the trajectory. Endpoint precision was comparable between patients with mild amblyopia and control participants. Patients with severe amblyopia had reduced endpoint precision along azimuth and elevation during amblyopic eye viewing only, and along the depth axis in all viewing conditions. In addition, they had significantly higher R2 values at 70% of movement time along the elevation and depth axes during amblyopic eye viewing. Conclusion Sensory uncertainty due to amblyopia leads to reduced precision of the motor plan. The ability to implement online corrections depends on the severity of the visual deficit, viewing condition, and the axis of the reaching movement. Patients with mild amblyopia used online control effectively to compensate for the reduced precision of the motor plan. In contrast, patients with severe amblyopia were not able to use online control as effectively to amend the limb trajectory especially along the depth axis, which could be due to their abnormal stereopsis.
Altered sense of Agency in children with spastic cerebral palsy
Anina Ritterband-Rosenbaum, Mark S Christensen, Mette Kliim-Due, Line Z Petersen, Betina Rasmussen, Jens B Nielsen
BMC Neurology , 2011, DOI: 10.1186/1471-2377-11-150
Abstract: Three groups; 1) CP children, 2) healthy peers, and 3) healthy adults produced straight drawing movements on a pen-tablet which was not visible for the subjects. The produced movement was presented as a virtual moving object on a computer screen. Subjects had to evaluate after each trial whether the movement of the object on the computer screen was generated by themselves or by a computer program which randomly manipulated the visual feedback by angling the trajectories 0, 5, 10, 15, 20 degrees away from target.Healthy adults executed the movements in 310 seconds, whereas healthy children and especially CP children were significantly slower (p < 0.002) (on average 456 seconds and 543 seconds respectively). There was also a statistical difference between the healthy and age matched CP children (p = 0.037). When the trajectory of the object generated by the computer corresponded to the subject's own movements all three groups reported that they were responsible for the movement of the object. When the trajectory of the object deviated by more than 10 degrees from target, healthy adults and children more frequently than CP children reported that the computer was responsible for the movement of the object. CP children consequently also attempted to compensate more frequently from the perturbation generated by the computer.We conclude that CP children have a reduced ability to determine whether movement of a virtual moving object is caused by themselves or an external source. We suggest that this may be related to a poor integration of their intention of movement with visual and proprioceptive information about the performed movement and that altered sense of agency may be an important functional problem in children with CP.Although CP is commonly described as a non-progressive disorder of normal sensory-motor development, new research has emphasized that CP also involves alteration of perception and cognitive abilities depending on the site, extent and time during devel
Freedom, choice, and the sense of agency  [PDF]
Zeynep Barlas,Sukhvinder S. Obhi
Frontiers in Human Neuroscience , 2013, DOI: 10.3389/fnhum.2013.00514
Abstract: The sense of agency is an intriguing aspect of human consciousness and is commonly defined as the sense that one is the author of their own actions and their consequences. In the current study, we varied the number of action alternatives (one, three, seven) that participants could select from and determined the effects on intentional binding which is believed to index the low-level sense of agency. Participants made self-paced button presses while viewing a conventional Libet clock and reported the perceived onset time of either the button presses or consequent auditory tones. We found that the binding effect was strongest when participants had the maximum number of alternatives, intermediate when they had medium level of action choice and lowest when they had no choice. We interpret our results in relation to the potential link between agency and the freedom to choose one’s actions.
Reaching within a dynamic virtual environment
Assaf Y Dvorkin, Robert V Kenyon, Emily A Keshner
Journal of NeuroEngineering and Rehabilitation , 2007, DOI: 10.1186/1743-0003-4-23
Abstract: Five healthy subjects were seated in front of an immersive, stereo virtual scene while reaching for a visual target that remained stationary in space or unpredictably shifted to a second position (either to the right or left of the first target) with different inter-stimulus intervals. Motion of the scene either matched the motion of their head or was rotated counter clockwise at 130 deg/s in the roll plane.Initial results suggested that both the temporal and spatial aspects of reaching were affected by a rolling visual field. Subjects were able to amend ongoing motion to match target position regardless of scene motion, but the presence of visual field motion produced significantly longer pauses during the reach movement when the target was shifted in space. In addition, terminal arm posture exhibited a drift in the direction opposite to the roll motion.These findings suggest that roll motion of the visual field of view interfered with the ability to imultaneously process two consecutive stimuli. Observed changes in arm position following the termination of the reach suggest that subjects were compensating for a perceived change in their visual reference frame.During the execution of a motor task, the central nervous system (CNS) monitors online body orientation by updating the internal representation of visual space. Studies have shown that both young and elderly healthy subjects are able to amend their ongoing movements in response to target displacement during a "double-step" paradigm which changes the spatial goal of the movement by unexpectedly changing the location of a visual target [1-4]. However, these movements have only been tested in stationary visual environments. During most active motions the individual and the external world are moving at the same time. While there is ample evidence that dynamic visual inputs affect motor behavior, (e.g., disrupting upper extremity movement trajectory and endpoint [5] and increasing postural instability [6,7]), the
Neural correlates of learning and trajectory planning in the posterior parietal cortex  [PDF]
Elizabeth B. Torres,Rodrigo Quian Quiroga,He Cui,Christopher A. Buneo
Frontiers in Integrative Neuroscience , 2013, DOI: 10.3389/fnint.2013.00039
Abstract: The posterior parietal cortex (PPC) is thought to play an important role in the planning of visually-guided reaching movements. However, the relative roles of the various subdivisions of the PPC in this function are still poorly understood. For example, studies of dorsal area 5 point to a representation of reaches in both extrinsic (endpoint) and intrinsic (joint or muscle) coordinates, as evidenced by partial changes in preferred directions and positional discharge with changes in arm posture. In contrast, recent findings suggest that the adjacent medial intraparietal area (MIP) is involved in more abstract representations, e.g., encoding reach target in visual coordinates. Such a representation is suitable for planning reach trajectories involving shortest distance paths to targets straight ahead. However, it is currently unclear how MIP contributes to the planning of other types of trajectories, including those with various degrees of curvature. Such curved trajectories recruit different joint excursions and might help us address whether their representation in the PPC is purely in extrinsic coordinates or in intrinsic ones as well. Here we investigated the role of the PPC in these processes during an obstacle avoidance task for which the animals had not been explicitly trained. We found that PPC planning activity was predictive of both the spatial and temporal aspects of upcoming trajectories. The same PPC neurons predicted the upcoming trajectory in both endpoint and joint coordinates. The predictive power of these neurons remained stable and accurate despite concomitant motor learning across task conditions. These findings suggest the role of the PPC can be extended from specifying abstract movement goals to expressing these plans as corresponding trajectories in both endpoint and joint coordinates. Thus, the PPC appears to contribute to reach planning and approach-avoidance arm motions at multiple levels of representation.
Doctoral Students’ Sense of Relational Agency in Their Scholarly Communities
Kirsi Pyh?lt?,Jenni Keskinen
International Journal of Higher Education , 2012, DOI: 10.5430/ijhe.v1n2p136
Abstract: The literature emphasizes the importance of integrating doctoral students into scholarly communities and practices at the very beginning of their studies. Although the importance of student participation in a scholarly community has been recognized empirical evidence concerning the quality of participation that promotes such engagement is scarce. This study focuses on exploring doctoral students’ sense of relational agency in terms of their scholarly communities and how this is related to study persistence and experienced socio-psychological well-being. Altogether 669 doctoral candidates from three faculties (humanities, medicine, and behavioural sciences) from a large research-intensive Finnish University completed a doctoral student survey. The results showed that a minority of the students perceived themselves as active relational agents in terms of their scholarly communities. However, students who perceived themselves as active relational agents experienced less lack of interest in their studies, less negative emotions, and less often considered abandoning their studies than students who perceived themselves as passive objects in their communities.
The independence of deficits in position sense and visually guided reaching following stroke  [cached]
Dukelow Sean P,Herter Troy M,Bagg Stephen D,Scott Stephen H
Journal of NeuroEngineering and Rehabilitation , 2012, DOI: 10.1186/1743-0003-9-72
Abstract: Background Several studies have found correlations between proprioception and visuomotor function during stroke recovery, however two more recent studies have found no correlation. Unfortunately, most of the studies to date have been conducted with clinical assessments of sensation that are observer-based and have poor reliability. We have recently developed new tests to assess position sense and motor function using robotic technology. The present study was conducted to reassess the relationship between position sense and upper limb movement following stroke. Methods We assessed position sense and motor performance of 100 inpatient stroke rehabilitation subjects and 231 non-disabled controls. All subjects completed quantitative assessments of position sense (arm-position matching task) and motor performance (visually-guided reaching task) using the KINARM robotic device. Subjects also completed clinical assessments including handedness, vision, Purdue Pegboard, Chedoke-McMaster Stroke Assessment-Impairment Inventory and Functional Independence Measure (FIM). Neuroimaging documented lesion localization. Fisher’s exact probability tests were used to determine the relationship between performances on the arm-position matching and visually-guided reaching task. Pearson’s correlations were conducted to determine the relationship between robotically measured parameters and clinical assessments. Results Performance by individual subjects on the matching and reaching tasks was statistically independent (Fisher’s test, P<0.01). However, performance on the matching and reaching tasks both exhibited relationships with abilities in daily activities as measured by the FIM. Performance on the reaching task also displayed strong relationships with other clinical measures of motor impairment. Conclusions Our data support the concept that position sense deficits are functionally relevant and point to the importance of assessing proprioceptive and motor impairments independently when planning treatment strategies.
A sense of agency: Utilising firms in the public relations campaigns course
Vince Benigni,J. Christopher Wood,Glen Cameron
PRism Online PR Journal , 2008,
Abstract: Extending Benigni and Cameron (1999) and subsequent works, this article espouses the notion of agency partnership in the public relations campaigns course. Because 90 percent of U.S. campaigns’ professors utilise an “agency structure” in this capstone course, it stands to reason that area firms are a natural bridge to fully embracing the concept. The authors examine pedagogical, role definition, and careerist literature, and offer a 10-part list of best practices for agency partnership.
Visuomotor Learning Enhanced by Augmenting Instantaneous Trajectory Error Feedback during Reaching  [PDF]
James L. Patton, Yejun John Wei, Preeti Bajaj, Robert A. Scheidt
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0046466
Abstract: We studied reach adaptation to a 30° visuomotor rotation to determine whether augmented error feedback can promote faster and more complete motor learning. Four groups of healthy adults reached with their unseen arm to visual targets surrounding a central starting point. A manipulandum tracked hand motion and projected a cursor onto a display immediately above the horizontal plane of movement. For one group, deviations from the ideal movement were amplified with a gain of 2 whereas another group experienced a gain of 3.1. The third group experienced an offset equal to the average error seen in the initial perturbations, while a fourth group served as controls. Learning in the gain 2 and offset groups was nearly twice as fast as controls. Moreover, the offset group averaged more reduction in error. Such error augmentation techniques may be useful for training novel visuomotor transformations as required of robotic teleoperators or in movement rehabilitation of the neurologically impaired.
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