Abstract
This study examines the source of directiondependent errors in movement extent made by human subjects in a reaching task. As in the preceding study, subjects were to move a cursor on a digitizing tablet to targets displayed on a computer monitor. Movements were made without concurrent visual feedback of cursor position, but movement paths were displayed on the monitor after the completion of each movement. We first examined horizontal hand movements made at waist level with the upper arm in a vertical orientation. Targets were located at five distances and two directions (30° and 150°) from one of two initial positions. Trajectory shapes were stereotyped, and movements to more distant targets had larger accelerations and velocities. Comparison of movements in the two directions showed that in the 30° direction responses were hypermetric, accelerations and velocities were larger, and movement times were shorter. Since movements in the 30° direction required less motion of the upper arm than movements in the 150° direction, we hypothesized that the differences in accuracy and acceleration reflected a failure to take into account the difference in total limb inertia in the two directions. To test this hypothesis we simulated the initial accelerations of a two-segment limb moving in the horizontal plane with the hand at shoulder level when a constant force was applied at the hand in each of 24 directions. We compared these simulated accelerations to ones produced by our subjects with their arms in the same position when they aimed movements to targets in the 24 directions and at equal distances from an initial position. The magnitudes of both simulated and actual accelerations were greatest in the two directions perpendicular to the forearm, where inertial resistance is least, and lowest for movements directed along the axis of the forearm. In all subjects, the directional variation in peak acceleration was similar to that predicted by the model and shifted in the same way when the initial position of the hand was displaced. The pattern of direction-dependent variations in initial acceleration did not depend on the speed of movement. It was also unchanged when subjects aimed their movements toward targets presented within the workspace on the tablet instead of on the computer monitor. These findings indicate that, in programming the magnitude of the initial force that will accelerate the hand, subjects do not fully compensate for direction-dependent differences in inertial resistance. The direction-dependent differences in peak acceleration were associated with systematic variations in movement extent in all subjects, but the variations in extent were proportionately smaller than those in acceleration. This compensation for inertial anisotropy, which differed in degree among subjects, was associated with changes in movement duration. The possible contributions of elastic properties of the musculoskeletal system and proprioceptive feed-back to the compensatory variations in movement time are discussed. The finding that the magnitude of the initial force that accelerates the hand is planned without regard to movement direction adds support for the hypothesis that extent and direction of an intended movement are planned independently. Furthermore, the lack of compensation for inertia in the acceleration of the simple reaching movements studied here suggests that they are planned by the central nervous system without explicit inverse kinematic and dynamic computations.
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References
Atkeson CG, Hollerbach JM (1985) Kinematic features of unrestrained vertical arm movements. J Neurosci 5:2318–2330
Bizzi E, Accornero N, Chappie W, Hogan N (1984) Posture control and trajectory formation during arm movement. J Neurosci 4:2738–2744
Brady M, Hollerbach JM, Johnson TL, Lozano-Pérez T, Mason M (1982) Robot motion: planning and control. MIT, Cambridge, MA
Burnod Y, Grandguillaume P, Otto I, Ferraina S, Johnson PB, Caminiti R (1992) Visuomotor transformations underlying arm movements toward visual targets: a neural network model of cerebral cortical operations. J Neurosci 12:1435–1453
Cleveland WS (1979) Robust locally weighted regression and smoothing scatterplots. J Am Stat Assoc 74:829–836
Favilla M, Hening W, Ghez C (1989) Trajectory control in targeted force impulses. VI. Independent specification of response amplitude and direction. Exp Brain Res 75:280–294
Favilla M, Gordon J, Hening W, Ghez C (1990) Trajectory control in targeted force impulses. VII. Independent setting of amplitude and direction in response preparation. Exp Brain Res 79:530–538
Feldman AG (1986) Once more on the equilibrium-point hypothesis (X model) for motor control. J Mot Behav 18:17–54
Flanders M, Helms Tillery SI, Soechting JF (1992) Early stages in a sensorimotor transformation. Behav Brain Sci 15:309–362
Flash T (1987) The control of hand equilibrium trajectories in multi-joint arm movements. Biol Cybern 57:257–274
Flash T, Mussa-Ivaldi F (1990) Human arm stiffness characteristics during the maintenance of posture. Exp Brain Res 82:315–326
Georgopoulos AP (1991) Higher order motor control. Annu Rev Neurosci 14:361–378
Georgopoulos AP, Ashe J, Smyrnis N, Taira M (1992) The motor cortex and the coding offeree. Science 256:1692–1695
Ghez C (1979) Contributions of central programs to rapid limb movements in the cat. In: Asanuma H, Wilson VJ (eds) Integration in the nervous system. Igaku-Shoin, Tokyo, pp 305–320
Ghez C, Vicario DS (1978) The control of rapid limb movement in the cat. II. Scaling of isometric force adjustments. Exp Brain Res 33:191–202
Ghez C, Gordon J, Ghilardi MF, Christakos CN, Cooper SE (1990a) Roles of proprioceptive input in the programming of arm trajectories. Cold Spring Harb Symp Quant Biol 55:837–847
Ghez C, Hening W, Favilla M (1990b) Parallel interacting channels in the initiation and specification of motor response features. In: Jeannerod M (eds) Motor representation and control. (Attention and performance, vol XIII) Erlbaum, Hillsdale, NJ, pp 265–293
Ghilardi MF, Gordon J, Ghez C (1991) Systematic directional errors in planar arm movements are reduced by vision of the arm. Soc Neurosci Abstr 17:1388
Ghilardi MF, Gordon J, Ghez C (1993) Directional biases in targeted arm movements result from distortions in the representation of the workspace. Soc Neurosci Abstr 19:1686
Gordon J, Ghez C (1987) Trajectory control in targeted force impulses. II. Pulse height control. Exp Brain Res 67:241–252
Gordon J, Ghez C (1989) Independence of direction and amplitude errors in planar arm movements. Soc Neurosci Abstr 15:50
Gordon J, Ghez C (1991) Muscle receptors and spinal reflexes: the stretch reflex. In: Kandel ER, Schwartz JH, Jessell TM (eds) Principles of neural science Elsevier, New York, pp 564–580
Gordon J, Ghilardi MF, Ghez C (1990) Deafferented subjects fail to compensate for workspace anisotropies in 2-dimensional arm movements. Soc Neurosci Abstr 16:1089
Gordon J, Ghilardi MF, Ghez C (1992a) In reaching, the task is to move the hand to a target. Behav Brain Sci 15:337–339
Gordon J, Ghilardi MF, Ghez C (1992b) Parallel processing of direction and extent in reaching movements. Eng Med Biol 11:92–93
Gordon J, Ghilardi MF, Ghez C (1994) Accuracy of planar reaching movements. I. Independence of direction and extent variability. Exp Brain Res 99:97–111
Hasan Z (1991) Biomechanics and the study of multijoint movements. In: Humphrey DR, Freund H-J (eds) Motor control: concepts and issues. Wiley, Chichester, pp 75–84
Hening W, Vicario D, Ghez C (1988) Trajectory control in targeted force impulses. IV. Influences of choice, prior experience and urgency. Exp Brain Res 71:103–115
Hogan N (1985) The mechanics of multi-joint posture and movement control. Biol Cybern 52:315–331
Hogan N (1988) Planning and execution of multijoint movements. Can J Physiol Pharmacol 66:508–517
Hollerbach JM (1982) Computers, brains and the control of movement. Trends Neurosci 5:189–192
Hollerbach JM, Flash T (1982) Dynamic interactions between limb segments during planar arm movement. Biol Cybern 44:67–77
Houk JC, Rymer WZ (1981) Neural control of muscle length and tension. In: Brooks VB (eds) Motor control. (Handbook of physiology, sect 1, The nervous system, vol 2, part 1) American Physiological Society, Bethesda, MD, pp 257–323
Kalaska JF, Cohen DAD, Hyde ML, Prud'homme M (1989) A comparison of movement direction-related versus load direction-related activity in primate motor cortex, using a two-dimensional reaching task. J Neurosci 9:2080–2102
Karst GM (1991) Characteristics of hand path curvature for planar multi-joint arm movements. Soc Neurosci Abstr 17:1387
Karst GM, Hasan Z (1991a) Initiation rules for planar, two-joint arm movements: agonist selection for movements throughout the work space. J Neurophysiol 66:1579–1593
Karst GM, Hasan Z (1991b) Timing and magnitude of electromyographic activity for two-joint arm movements in different directions. J Neurophysiol 66:1594–1604
Merton PA (1953) Speculations on the servo-control of movement. In: Wolstenholme GEW (eds) The spinal cord. Churchill Livingstone, London, pp 247–255
Mussa-Ivaldi FA, Hogan N, Bizzi E (1985) Neural, mechanical, and geometric factors subserving arm posture in humans. J Neurosci 5:2732–2743
Poulton EC (1981) Human manual control. In: Brooks VB (eds) Motor Control. (Handbook of physiology, sect 1, The nervous system, vol 2, part 2) American Physiological Society, Bethesda, MD, pp 1337–1389
Sainburg RL, Ghilardi MF, Ferracci F, Poizner H, Ghez C (1992) Role of proprioceptive input in the control of interaction torques during multijoint movements. Soc Neurosci Abstr 18:1550
Sainburg RL, Ghilardi MF, Poizner H, Ghez C (1993) Vision of the limb allows deafferented patients to control multi-joint dynamics. Soc Neurosci Abstr 1686
Saltzman E (1979) Levels of sensorimotor representation. J Math Psychol 20:91–163
Shadmehr R, Mussa-Ivaldi FA, Bizzi E (1993) Postural force fields of the human arm and their role in generating multi-joint movements. J Neurosci 13:45–62
Smith JL, Zernicke RF (1987) Predictions for neural control based on limb dynamics. Trends Neurosci 10:123–128
Soechting JF (1989) Elements of coordinated arm movements in three-dimensional space. In: Wallace SA (eds) Perspectives on the coordination of movement. North-Holland, New York, pp 47–83
Vallbo ÅB (1970) Discharge patterns in human muscle spindle afferents during isometric voluntary contractions. Acta Physiol Scand 80:552–566
Winter DA (1990) Biomechanics and motor control of human movement. Wiley, New York
Worringham CJ (1992) Some historical roots of phenomena and methods in motor behavior research. In: Stelmach GE, Requin J (eds) Tutorials in motor behavior II. North-Holland, Amsterdam, pp 807–825
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Gordon, J., Ghilardi, M.F., Cooper, S.E. et al. Accuracy of planar reaching movements. Exp Brain Res 99, 112–130 (1994). https://doi.org/10.1007/BF00241416
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DOI: https://doi.org/10.1007/BF00241416