Biomedical subjects

Elizabeth B Torres

Publications and source records attributed to Elizabeth B Torres.

2 recordsLinked to original sources

PubMed2003

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

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.

Arm↗

PubMed2002

Reaching to grasp with a multi-jointed arm. I. Computational model.

The generation of goal-directed movements requires the solution of many difficult computational problems. Among these are transformations from extrinsic to intrinsic reference frames, specifying solution paths, removing under-specification due to excess degrees of freedom and path multiplicity, constraint satisfaction, and error correction. There are no current motor-control computational models that address these issues in the context of realistic arm movement with redundant degrees of freedom. In this paper, we conjecture there is a geometric stage between sensory input and physical execution. The geometric stage determines movement trajectories independently of forces. It uses a gradient technique that relies on the metric of the space of postures to resolve endpoint path selection, posture-change specification, error correction, and multiple constraint satisfaction on-line without preplanning. The model is instantiated in an arm with seven degrees of freedom that moves in three-dimensional space. Simulated orientation-matching movements are compared with actual human movement data to assess the validity of several of the model's behavioral predictions.

Algorithms↗