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Robert Volcic, Fulvio Domini; Visual on-line control of grasping movements. Journal of Vision 2014;14(10):902. doi: 10.1167/14.10.902.
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© ARVO (1962-2015); The Authors (2016-present)
Seeing your hand while grasping self-evidently affects the action in progress. Observers could potentially use visual feedback to adjust the trajectory of the moving limb, or to shape the posture of the hand and fingers, or both. Here, we investigated how the visually sensed finger grip aperture influences the on-line control of grasping movements. We used a dynamic perturbation method that altered the position of the visual feedback relative to the actual position of the thumb and index fingertips to virtually increase/decrease the actual grip aperture. Importantly, the virtual grip aperture was smoothly altered only when the actual grip aperture was larger than the size of the object to be grasped. In this way, the perturbation was present during most of the movement, but vanished the moment the fingers contacted the object. Subjects performed grasping movements in a virtual environment with haptic feedback. Visual feedback of the hand was provided by rendering virtual spheres representing the subject's thumb and index fingertips. The virtual grip aperture was smaller than, larger than, or equal to the actual grip aperture. These perturbations were presented in a randomized order to prevent adaptation. Despite the substantial changes of the virtual grip aperture, the actual grip aperture was unaffected. However, we found that the virtual grip aperture modulated specific aspects of reach and grasp dynamics. The smaller the virtual grip aperture, the earlier the peak wrist deceleration occurred, the later the grip aperture reached its maximum, and, the later the fingers enclosed the object. Moreover, the virtual grip aperture affected fine-tuned adjustments of the hand position when in the immediate vicinity of the object. These findings provide evidence that the visual feedback of the hand is more involved in the direct control of the moving limb, than in the control of the grip aperture.
Meeting abstract presented at VSS 2014
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