Planning of reach-and-grasp movements: effects of validity and type of object information.

Individuals are assumed to plan reach-and-grasp movements by using two separate processes. In 1 of the processes, extrinsic (direction, distance) object information is used in planning the movement of the arm that transports the hand to the target location (transport planning); whereas in the other, intrinsic (shape) object information is used in planning the preshaping of the hand and the grasping of the target object (manipulation planning). In 2 experiments, the authors used primes to provide information to participants (N = 5, Experiment 1; N = 6, Experiment 2) about extrinsic and intrinsic object properties.

Finding final postures.

In this study, a model of movement planning (Rosenbaum, Engelbrecht, Bushe, & Loukopoulos, 1993a, 1993b; Rosenbaum, Loukopoulos, Meulenbroek, Vaughan, & Engelbrecln, 1995), in which movements are generated on the basis of the efficacy of different possible goal postures, was tested. The model predicts which limb segments will be used and how the segments will be combined in reaching. The model's predictions were compared with observations from a study in which seated participants reached for targets in a sagittal plane, using the hip, shoulder, and elbow.

Adaptation of a reaching model to handwriting: how different effectors can produce the same written output, and other results.

This report shows how a model initially developed for the control of reaching can be adapted for the control of handwriting. The main problem addressed by the model is how people can produce essentially the same written output with different effectors (e.g.

Planning reaches by evaluating stored postures.

This article describes a theory of the computations underlying the selection of coordinated motion patterns, especially in reaching tasks. The central idea is that when a spatial target is selected as an object to be reached, stored postures are evaluated for the contributions they can make to the task. Weights are assigned to the stored postures, and a single target posture is found by taking a weighted sum of the stored postures.

Knowledge Model for Selecting and Producing Reaching Movements.

This article presents a new model of reaching control. The aim of the model is to characterize the computations underlying the selection of coordinated motion patterns among the limb segments. When a spatial target is selected, stored postures are evaluated for the contributions they can make to the task, and a special weighted average (the gaussian average) is taken of the postures to find a single target posture.