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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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Force VectorsThe cartoons depict the arm configurations in the training and transfer positions for all six combinations of object condition (columns) and arm configuration (top and bottom panels). Participants stretched an elastic band (red lines) to a nearby target (black circles) with their right hand. Each blue cross represents the median force vector generated by a given participant during catch trials after learning. The thick blue lines show mean force vectors, averaged across participants, and the blue ellipses represent the corresponding 50% confidence ellipses. Each green cross represents the median force vector during transfer trials after learning in the training position. The thick green lines show mean force vectors, averaged across participants, and the green ellipses represent the corresponding 50% confidence ellipses. The predicted force-vector directions based on transfer in object- and arm-centered coordinates are represented by the dashed and dotted lines, respectively.
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fig2: Force VectorsThe cartoons depict the arm configurations in the training and transfer positions for all six combinations of object condition (columns) and arm configuration (top and bottom panels). Participants stretched an elastic band (red lines) to a nearby target (black circles) with their right hand. Each blue cross represents the median force vector generated by a given participant during catch trials after learning. The thick blue lines show mean force vectors, averaged across participants, and the blue ellipses represent the corresponding 50% confidence ellipses. Each green cross represents the median force vector during transfer trials after learning in the training position. The thick green lines show mean force vectors, averaged across participants, and the green ellipses represent the corresponding 50% confidence ellipses. The predicted force-vector directions based on transfer in object- and arm-centered coordinates are represented by the dashed and dotted lines, respectively.

Mentions: Six different groups of participants experienced one of three object conditions in one of two arm configurations (FigureĀ 2). In the straight-visible condition, the elastic band was visible and directly linked between the hands to create an object with relatively simple dynamics. The straight-invisible condition was the same except that the band was not visible. In the pulley condition, the visible band was wrapped around a virtual pulley to create an object with more complex dynamics. Therefore, in the pulley condition the experienced force at the left hand is not parallel to the movement direction of the right hand, whereas, in the straight conditions, the experienced force is parallel to the movement direction of the right hand. Each of these conditions was tested in two arm configurations with the end of the band attached to the left hand oriented in either the transverse or sagittal plane.


Flexible representations of dynamics are used in object manipulation.

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

Force VectorsThe cartoons depict the arm configurations in the training and transfer positions for all six combinations of object condition (columns) and arm configuration (top and bottom panels). Participants stretched an elastic band (red lines) to a nearby target (black circles) with their right hand. Each blue cross represents the median force vector generated by a given participant during catch trials after learning. The thick blue lines show mean force vectors, averaged across participants, and the blue ellipses represent the corresponding 50% confidence ellipses. Each green cross represents the median force vector during transfer trials after learning in the training position. The thick green lines show mean force vectors, averaged across participants, and the green ellipses represent the corresponding 50% confidence ellipses. The predicted force-vector directions based on transfer in object- and arm-centered coordinates are represented by the dashed and dotted lines, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

fig2: Force VectorsThe cartoons depict the arm configurations in the training and transfer positions for all six combinations of object condition (columns) and arm configuration (top and bottom panels). Participants stretched an elastic band (red lines) to a nearby target (black circles) with their right hand. Each blue cross represents the median force vector generated by a given participant during catch trials after learning. The thick blue lines show mean force vectors, averaged across participants, and the blue ellipses represent the corresponding 50% confidence ellipses. Each green cross represents the median force vector during transfer trials after learning in the training position. The thick green lines show mean force vectors, averaged across participants, and the green ellipses represent the corresponding 50% confidence ellipses. The predicted force-vector directions based on transfer in object- and arm-centered coordinates are represented by the dashed and dotted lines, respectively.
Mentions: Six different groups of participants experienced one of three object conditions in one of two arm configurations (FigureĀ 2). In the straight-visible condition, the elastic band was visible and directly linked between the hands to create an object with relatively simple dynamics. The straight-invisible condition was the same except that the band was not visible. In the pulley condition, the visible band was wrapped around a virtual pulley to create an object with more complex dynamics. Therefore, in the pulley condition the experienced force at the left hand is not parallel to the movement direction of the right hand, whereas, in the straight conditions, the experienced force is parallel to the movement direction of the right hand. Each of these conditions was tested in two arm configurations with the end of the band attached to the left hand oriented in either the transverse or sagittal plane.

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.

Show MeSH
Related in: MedlinePlus