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HIGHLIGHTED TOPICS
Neural Control of Movement

Simultaneous control of hand displacements and rotations in orientation-matching experiments

¹Division of Biology, California Institute of Technology, Pasadena 91125; and ²Department of Cognitive Science, University of California, San Diego, La Jolla, California 92093-0515

Submitted 18 August 2003 ; accepted in final form 9 December 2003

In reach-to-grasp movements, the interaction between the hand changes in position and those in orientation is poorly understood. A theoretical approach previously proposed (Torres EB and Zipser D. J Neurophysiol 88: 1-13, 2002) assumes that motion strategies are resolved in space independently from the temporal dynamics of the motion and predicts the coarticulation of the hand transport and rotation along the path. The model implies that this simultaneous control is independent of variations in speed and initial posture and required matching orientation. This paper presents experimental data from human subjects that confirm the model's predictions in the context of realistic, unconstrained, orientation-matching motions. Speed independence is quantified in the similarity of the postural and endpoint position-orientation paths obtained under three different speeds. Significant differences in hand and joint kinematics are shown in response to changes in initial posture and target orientation. The robustness of coarticulation under all three experimental conditions supports the idea of an intermediate stage that resolves the geometry of the motion independent of its temporal dynamics.

temporal dynamics; geometric stage; redundant degrees of freedom; sensorimotor transformation

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