Invariant characteristics of a pointing movement in man

Abstract

Simple arm movements involving forward projection of the hand toward a target were studied by measuring simultaneous wrist position in three-dimensional space and changes in elbow angle. An attempt was made to identify those features of the movement which exhibit invariant characteristics under the hypothesis that such invariances may reflect the operations by which central processes participate in the organization of the movement. The first such invariance to be identified was that the trajectory in space is independent of movement speed. Secondly, the movement can be viewed as consisting of two phases, an acceleratory phase and a deceleratory one, with the movement during the acceleratory phase being so organized as to maintain the ratio of elbow angular velocity to shoulder angular velocity invariant with respect to target location in the deceleratory phase. It is suggested that proprioceptive information is used to control the movement and that the latter invariance may result from a negative feedback of force involving tendon organ afferents.

Inter-joint coupling and joint angle synergies of human catching movements

“…Finding unambiguous solutions for this transformation is not a trivial task. The CNS overcomes this problem routinely and often generates reproducible behavior that exhibits invariant parameters, which have been observed in classical studies such as Soechting and Lacquaniti (1981), Atkeson and Hollerbach (1985), Morasso (1981), and Flash and Hogan (1985). The results of these studies imply additional constraints that are realized within the nervous system and have led to the formulation of a range of hypotheses concerning the generation of goal-directed limb movements.…”

Limb versus Speech Motor Control: A Conceptual Review

“…In modern movement science, the debate about extrinsic vs. intrinsic motor goals began with studies which found that some key properties of the movement trajectories of the end-effector were invariant in the outer Cartesian space, across repetitions, conditions, and subjects: movement paths of the endeffector are gently curved and their tangential velocity profiles are bell-shaped with a single peak (Morasso, 1981;Abend et al, 1982). Soechting and Lacquaniti (1981), studied pointing arm movements in a vertical plane and interpreted extrinsic invariants as the consequence of the temporal coordination of the joint angles at the shoulder and the elbow (see Flanagan and Ostry (1990) for a similar conclusion for jaw movements). Uno et al (1989) and Kawato et al (1990) argued that optimization principles may add intrinsic to extrinsic constraints.…”

Minimum Principles in Motor Control

“…At the time the minimum-jerk theory was proposed, it concisely summarized the majority of the available arm movement data: Morasso (1981) and Flash and Hogan (1985) had found straight hand paths for various horizontal-plane movements, Hollerbach and Flash (1982) and Soechting and Lacquaniti (1981) had reported data suggesting that trajectory shape is unaffected by changes in movement duration, and the studies of Abend et al (1982), Georgopoulos, Kalaska, and Massey (1981), and Morasso (1981) had shown that velocity profiles are bellshaped and approximately symmetric. Because of its excellent agreement with these experimental observations, the minimum-jerk principle became one of the most influential motor control theories.…”