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Flexible representations of dynamics are used in object manipulation.

Ahmed AA, Wolpert DM, Flanagan JR - Curr. Biol. (2008)

Bottom Line: These results indicate that object dynamics can be flexibly represented in different coordinate frames by the brain.We suggest that with experience, the representation of the dynamics of a manipulated object may shift from a coordinate frame tied to the arm toward one that is linked to the object.The additional complexity required to represent dynamics in object-centered coordinates would be economical for familiar objects because such a representation allows object use regardless of the orientation of the object in hand.

View Article: PubMed Central - PubMed

Affiliation: Computational and Biological Learning Lab, Department of Engineering, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
To manipulate an object skillfully, the brain must learn its dynamics, specifying the mapping between applied force and motion. A fundamental issue in sensorimotor control is whether such dynamics are represented in an extrinsic frame of reference tied to the object or an intrinsic frame of reference linked to the arm. Although previous studies have suggested that objects are represented in arm-centered coordinates [1-6], all of these studies have used objects with unusual and complex dynamics. Thus, it is not known how objects with natural dynamics are represented. Here we show that objects with simple (or familiar) dynamics and those with complex (or unfamiliar) dynamics are represented in object- and arm-centered coordinates, respectively. We also show that objects with simple dynamics are represented with an intermediate coordinate frame when vision of the object is removed. These results indicate that object dynamics can be flexibly represented in different coordinate frames by the brain. We suggest that with experience, the representation of the dynamics of a manipulated object may shift from a coordinate frame tied to the arm toward one that is linked to the object. The additional complexity required to represent dynamics in object-centered coordinates would be economical for familiar objects because such a representation allows object use regardless of the orientation of the object in hand.

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ApparatusWhile seated, participants grasped two handles, each attached to a planar, force-generating, two-joint, robotic manipulandum. The arms were supported by low-friction air sleds (not shown), which restricted arm motion to the horizontal plane. Participants looked down onto a horizontal semisilvered mirror, located above the hands, that displayed circles representing their hand positions in the plane of arm movement. In the straight-visible condition, participants also viewed an elastic band directly attached to the two handles (as shown in the figure), and in the pulley condition, they viewed an elastic band wrapped around a visible, rotating pulley (see Figure 2).
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fig1: ApparatusWhile seated, participants grasped two handles, each attached to a planar, force-generating, two-joint, robotic manipulandum. The arms were supported by low-friction air sleds (not shown), which restricted arm motion to the horizontal plane. Participants looked down onto a horizontal semisilvered mirror, located above the hands, that displayed circles representing their hand positions in the plane of arm movement. In the straight-visible condition, participants also viewed an elastic band directly attached to the two handles (as shown in the figure), and in the pulley condition, they viewed an elastic band wrapped around a visible, rotating pulley (see Figure 2).

Mentions: We used a bimanual object-manipulation task in which participants grasped two handles attached by a virtual elastic band (Figure 1) and moved the right hand to stretch the band while holding the left hand still. In this task, participants learn to compensate for the effects of right-hand movement by generating appropriate forces with the left hand [5, 7–9]. To test whether participants represent dynamics in object- or arm-centered coordinates, we examined how this learning transferred when the object was moved to a new location involving a change in arm configuration.


Flexible representations of dynamics are used in object manipulation.

Ahmed AA, Wolpert DM, Flanagan JR - Curr. Biol. (2008)

ApparatusWhile seated, participants grasped two handles, each attached to a planar, force-generating, two-joint, robotic manipulandum. The arms were supported by low-friction air sleds (not shown), which restricted arm motion to the horizontal plane. Participants looked down onto a horizontal semisilvered mirror, located above the hands, that displayed circles representing their hand positions in the plane of arm movement. In the straight-visible condition, participants also viewed an elastic band directly attached to the two handles (as shown in the figure), and in the pulley condition, they viewed an elastic band wrapped around a visible, rotating pulley (see Figure 2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2387196&req=5

fig1: ApparatusWhile seated, participants grasped two handles, each attached to a planar, force-generating, two-joint, robotic manipulandum. The arms were supported by low-friction air sleds (not shown), which restricted arm motion to the horizontal plane. Participants looked down onto a horizontal semisilvered mirror, located above the hands, that displayed circles representing their hand positions in the plane of arm movement. In the straight-visible condition, participants also viewed an elastic band directly attached to the two handles (as shown in the figure), and in the pulley condition, they viewed an elastic band wrapped around a visible, rotating pulley (see Figure 2).
Mentions: We used a bimanual object-manipulation task in which participants grasped two handles attached by a virtual elastic band (Figure 1) and moved the right hand to stretch the band while holding the left hand still. In this task, participants learn to compensate for the effects of right-hand movement by generating appropriate forces with the left hand [5, 7–9]. To test whether participants represent dynamics in object- or arm-centered coordinates, we examined how this learning transferred when the object was moved to a new location involving a change in arm configuration.

Bottom Line: These results indicate that object dynamics can be flexibly represented in different coordinate frames by the brain.We suggest that with experience, the representation of the dynamics of a manipulated object may shift from a coordinate frame tied to the arm toward one that is linked to the object.The additional complexity required to represent dynamics in object-centered coordinates would be economical for familiar objects because such a representation allows object use regardless of the orientation of the object in hand.

View Article: PubMed Central - PubMed

Affiliation: Computational and Biological Learning Lab, Department of Engineering, University of Cambridge, Cambridge, United Kingdom.

ABSTRACT
To manipulate an object skillfully, the brain must learn its dynamics, specifying the mapping between applied force and motion. A fundamental issue in sensorimotor control is whether such dynamics are represented in an extrinsic frame of reference tied to the object or an intrinsic frame of reference linked to the arm. Although previous studies have suggested that objects are represented in arm-centered coordinates [1-6], all of these studies have used objects with unusual and complex dynamics. Thus, it is not known how objects with natural dynamics are represented. Here we show that objects with simple (or familiar) dynamics and those with complex (or unfamiliar) dynamics are represented in object- and arm-centered coordinates, respectively. We also show that objects with simple dynamics are represented with an intermediate coordinate frame when vision of the object is removed. These results indicate that object dynamics can be flexibly represented in different coordinate frames by the brain. We suggest that with experience, the representation of the dynamics of a manipulated object may shift from a coordinate frame tied to the arm toward one that is linked to the object. The additional complexity required to represent dynamics in object-centered coordinates would be economical for familiar objects because such a representation allows object use regardless of the orientation of the object in hand.

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