Directional control of planar human arm movement

Daniel Corcos. Directional control of planar human arm movement. in the laboratory. Although studies usually avoid explicitly J. Neurophysiol. 78: 2985–2998, 1997. We examined the patterns of controlling other kinematic features of the movement, it hasjoint kinematics and torques in two kinds of sagittal plane reaching long been recognized that reaching movements share several movements. One consisted of movements from a fixed initial position distinctive and relatively invariant kinematic properties with the arm partially outstretched, to different targets, equidistant (Lacquaniti and Soechting 1982; Morasso 1981). For exam-from the initial position and located according to the hours of a clock. ple, the relatively straight paths and bell-shaped tangentialThe other series added movements from different initial positions and velocity profiles between the movements ’ end points indirections and 40–80 cm distances. Dynamic muscle torque was calculated by inverse dynamic equations with the gravitational compo- Cartesian space are little affected by either the intended nents removed. In making movements in almost every direction, the speed of movement or the addition of loads. Under some dynamic components of the muscle torques at both the elbow and conditions, linear relations also have been found between shoulder were related almost linearly to each other. Both were simi- joint angles (Atkeson and Hollerbach 1985; Hong et al.larly shaped, biphasic, almost synchronous and symmetrical pulses. 1994; Lacquaniti et al. 1986; Soechting and LacquanitiThese findings are consistent with our previously reported observa- 1981).tions, which we termed a linear synergy. The relative scaling of th