| 1. |
- Flanagan, J Randall, et al.
(author)
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Control strategies in object manipulation tasks.
- 2006
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In: Current Opinion in Neurobiology. - : Elsevier BV. - 0959-4388. ; 16:6, s. 650-9
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Journal article (other academic/artistic)abstract
- The remarkable manipulative skill of the human hand is not the result of rapid sensorimotor processes, nor of fast or powerful effector mechanisms. Rather, the secret lies in the way manual tasks are organized and controlled by the nervous system. At the heart of this organization is prediction. Successful manipulation requires the ability both to predict the motor commands required to grasp, lift, and move objects and to predict the sensory events that arise as a consequence of these commands.
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| 2. |
- Flanagan, J Randall, et al.
(author)
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Experience can change distinct size-weight priors engaged in lifting objects and judging their weights.
- 2008
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In: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 18:22, s. 1742-7
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Journal article (peer-reviewed)abstract
- The expectation that object weight increases with size guides the control of manipulatory actions [1-6] and also influences weight perception. Thus, the size-weight illusion, whereby people perceive the smaller of two equally weighted objects to be heavier, is thought to arise because weight is judged relative to expected weight that, for a given family of objects, increases with size [2, 7]. Here, we show that the fundamental expectation that weight increases with size can be altered by experience and neither is hard-wired nor becomes crystallized during development. We demonstrate that multiday practice in lifting a set of blocks whose color and texture are the same and whose weights vary inversely with volume gradually attenuates and ultimately inverts the size-weight illusion tested with similar blocks. We also show that in contrast to this gradual change in the size-weight illusion, the sensorimotor system rapidly learns to predict the inverted object weights, as revealed by lift forces. Thus, our results indicate that distinct adaptive size-weight maps, or priors, underlie weight predictions made in lifting objects and in judging their weights. We suggest that size-weight priors that influence weight perception change slowly because they are based on entire families of objects. Size-weight priors supporting action are more flexible, and adapt more rapidly, because they are tuned to specific objects and their current state.
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| 3. |
- Flanagan, J Randall, et al.
(author)
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Gaze behavior when reaching to remembered targets.
- 2008
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In: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 100:3, s. 1533-43
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Journal article (peer-reviewed)abstract
- People naturally direct their gaze to visible hand movement goals. Doing so improves reach accuracy through use of signals related to gaze position and visual feedback of the hand. Here, we studied where people naturally look when acting on remembered target locations. Four targets were presented on a screen, in peripheral vision, while participants fixed a central cross (encoding phase). Four seconds later, participants used a pen to mark the remembered locations while free to look wherever they wished (recall phase). Visual references, including the screen and the cross, were present throughout. During recall, participants neither looked at the marked locations nor prevented eye movements. Instead, gaze behavior was erratic and was comprised of gaze shifts loosely coupled in time and space with hand movements. To examine whether eye and hand movements during encoding affected gaze behavior during recall, in additional encoding conditions, participants marked the visible targets with either free gaze or with central cross fixation or just looked at the targets. All encoding conditions yielded similar erratic gaze behavior during recall. Furthermore, encoding mode did not influence recall performance, suggesting that participants, during recall, did not exploit sensorimotor memories related to hand and gaze movements during encoding. Finally, we recorded a similar lose coupling between hand and eye movements during an object manipulation task performed in darkness after participants had viewed the task environment. We conclude that acting on remembered versus visible targets can engage fundamentally different control strategies, with gaze largely decoupled from movement goals during memory-guided actions.
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| 4. |
- Flanagan, J Randall, et al.
(author)
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Predictive mechanisms and object representations used in object manipulation
- 2009
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In: Sensorimotor Control of Grasping. - Cambridge : Cambridge University Press. - 9780521881579 ; , s. 161-177
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Book chapter (pop. science, debate, etc.)abstract
- Skilled object manipulation requires the ability to estimate, in advance, the motor commands needed to achieve desired sensory outcomes and the ability to predict the sensory consequences of the motor commands. Because the mapping between motor commands and sensory outcomes depends on the physical properties of grasped objects, the motor system may store and access internal models of objects in order to estimate motor commands and predict sensory consequences. In this chapter, we outline evidence for internal models and discuss their role in object manipulation tasks. We also consider the relationship between internal models of objects employedby the sensorimotor system and representations of the same objects used by the perceptual system to make judgments about objects.
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| 5. |
- Johansson, Roland S, et al.
(author)
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Coding and use of tactile signals from the fingertips in object manipulation tasks
- 2009
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In: Nature Reviews Neuroscience. - : Springer Science and Business Media LLC. - 1471-003X .- 1471-0048. ; 10:5, s. 345-359
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Journal article (peer-reviewed)abstract
- During object manipulation tasks, the brain selects and implements action-phase controllers that use sensory predictions and afferent signals to tailor motor output to the physical properties of the objects involved. Analysis of signals in tactile afferent neurons and central processes in humans reveals how contact events are encoded and used to monitor and update task performance.
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| 6. |
- Johansson, Roland S, et al.
(author)
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Sensorimotor control of manipulation
- 2009. - 8
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In: Encyclopedia of Neuroscience. - : Elsevier. - 9780080450469 - 0080450466 ; , s. 593-604
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Book chapter (pop. science, debate, etc.)
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| 7. |
- Rotman, Gerben, et al.
(author)
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Eye movements when observing predictable and unpredictable actions.
- 2006
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In: Journal of Neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 96:3, s. 1358-69
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Journal article (peer-reviewed)abstract
- We previously showed that, when observers watch an actor performing a predictable block-stacking task, the coordination between the observer's gaze and the actor's hand is similar to the coordination between the actor's gaze and hand. Both the observer and the actor direct gaze to forthcoming grasp and block landing sites and shift their gaze to the next grasp or landing site at around the time the hand contacts the block or the block contacts the landing site. Here we compare observers' gaze behavior in a block manipulation task when the observers did and when they did not know, in advance, which of two blocks the actor would pick up first. In both cases, observers managed to fixate the target ahead of the actor's hand and showed proactive gaze behavior. However, these target fixations occurred later, relative to the actor's movement, when observers did not know the target block in advance. In perceptual tests, in which observers watched animations of the actor reaching partway to the target and had to guess which block was the target, we found that the time at which observers were able to correctly do so was very similar to the time at which they would make saccades to the target block. Overall, our results indicate that observers use gaze in a fashion that is appropriate for hand movement planning and control. This in turn suggests that they implement representations of the manual actions required in the task and representations that direct task-specific eye movements.
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| 8. |
- Sailer, Uta, et al.
(author)
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Eye-hand coordination during learning of a novel visuomotor task.
- 2005
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In: Journal of Neuroscience. - 1529-2401. ; 25:39, s. 8833-42
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Journal article (peer-reviewed)abstract
- We investigated how gaze behavior and eye-hand coordination change when subjects learned a challenging visuomotor task that required acquisition of a novel mapping between bimanual actions and their visual sensory consequences. By applying isometric forces and torques to a rigid tool held freely between the two hands, subjects learned to control a cursor on a computer screen to hit successively displayed targets as quickly as possible. The learning occurred in stages that could be distinguished by changes in performance (target-hit rate) as well as by gaze behavior and eye-hand coordination. In a first exploratory stage, the hit rate was consistently low, the cursor position varied widely, and gaze typically pursued the cursor. In a second skill acquisition stage, the hit rate improved rapidly, and gaze fixations began to mark predictively desired cursor positions, indicating that subjects started to program spatially congruent eye and hand motor commands. In a third skill refinement stage, performance continued to improve gradually, and gaze shifted directly toward the target. We suggest that during the exploratory stage, the learner attempts to establish basic mapping rules between manual actions and eye-movement commands. In this process, subjects may establish correlations between hand motor commands and their visual sensory consequences, primarily in fovea-anchored, gaze-centered coordinates, and correlations between recent hand motor commands and eye motor commands. The established mapping rules are then implemented and refined in the skill acquisition and refinement stages.
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