title: Planning maximally smooth hand movements constrained to nonplanar workspaces.
abstract: 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.
authors.affiliation: Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Israel. dlieberm@post.tau.ac.il
authors.forename: Dario G
authors.initials: DG
authors.lastname: Liebermann
authors.forename: Tal
authors.initials: T
authors.lastname: Krasovsky
authors.forename: Sigal
authors.initials: S
authors.lastname: Berman
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000465:Algorithms; D005260:Female; D006225:Hand / Q000502:physiology*; D006801:Humans; D033182:Intention; D007699:Kinesthesis / Q000502:physiology*; D008297:Male; D015233:Models, Statistical; D009068:Movement / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D012016:Reference Values; D014956:Writing