Planning maximally smooth hand movements constrained to nonplanar workspaces

J Mot Behav. 2008 Nov;40(6):516-31. doi: 10.3200/JMBR.40.6.516-531.


The article characterizes hand paths and speed profiles for movements performed in a nonplanar, 2-dimensional workspace (a hemisphere of constant curvature). The authors assessed endpoint kinematics (i.e., paths and speeds) under the minimum-jerk model assumptions and calculated minimal amplitude paths (geodesics) and the corresponding speed profiles. The authors also calculated hand speeds using the 2/3 power law. They then compared modeled results with the empirical observations. In all, 10 participants moved their hands forward and backward from a common starting position toward 3 targets located within a hemispheric workspace of small or large curvature. Comparisons of modeled observed differences using 2-way RM-ANOVAs showed that movement direction had no clear influence on hand kinetics (p < .05). Workspace curvature affected the hand paths, which seldom followed geodesic lines. Constraining the paths to different curvatures did not affect the hand speed profiles. Minimum-jerk speed profiles closely matched the observations and were superior to those predicted by 2/3 power law (p < .001). The authors conclude that speed and path cannot be unambiguously linked under the minimum-jerk assumption when individuals move the hand in a nonplanar 2-dimensional workspace. In such a case, the hands do not follow geodesic paths, but they preserve the speed profile, regardless of the geometric features of the workspace.

MeSH terms

  • Adaptation, Physiological
  • Adult
  • Algorithms
  • Female
  • Hand / physiology*
  • Humans
  • Intention*
  • Kinesthesis / physiology*
  • Male
  • Models, Statistical
  • Movement / physiology*
  • Psychomotor Performance / physiology*
  • Reference Values
  • Writing