Experimental Brain Research

, Volume 92, Issue 2, pp 326-337

First online:

Three-dimensional drawings in isometric conditions: planar segmentation of force trajectory

  • Giuseppe PellizzerAffiliated withBrain Sciences Center, Veterans Affairs Medical Center
  • , Joe T. MasseyAffiliated withDepartment of Physiology, University of Minnesota Medical School
  • , Joseph T. LuritoAffiliated withDepartment of Neuroscience, The Johns Hopkins University, School of Medicine
  • , Apostolos P. GeorgopoulosAffiliated withBrain Sciences Center, Veterans Affairs Medical Center

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Normal human subjects grasped an isometric handle with an unrestrained, pronated hand. They were asked to exert forces continuously to draw lemniscates (figure eights) in specified or self-chosen planes and in the presence or absence of a three-dimensional visual feedback cursor and a visual template. In every condition, the mean plane orientation in the force space differed appreciably between the two loops of the figure, as described previously by Soechting and Terzuolo (1987a) for free drawing arm movements. These findings suggest that the planar segmentation of the motor trajectory is not a consequence of joint motion but arises from central constraints related to the production of motor trajectory in space.

Key words

Force Trajectory Segmentation Human