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Author Liebermann, D.G.; Krasovsky, T.; Berman, S. url  doi
openurl 
  Title Planning maximally smooth hand movements constrained to nonplanar workspaces Type Journal Article
  Year 2008 Publication Journal of Motor Behavior Abbreviated Journal J Mot Behav  
  Volume 40 Issue 6 Pages 516-531  
  Keywords Adaptation, Physiological; Adult; Algorithms; Female; Hand/*physiology; Humans; *Intention; Kinesthesis/*physiology; Male; Models, Statistical; Movement/*physiology; Psychomotor Performance/*physiology; Reference Values; Writing  
  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.  
  Address Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel Aviv University, Israel. dlieberm@post.tau.ac.il  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN (down) 0022-2895 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:18980905 Approved no  
  Call Number Serial 33  
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Author Liebermann, D.G.; Goodman, D. url  doi
openurl 
  Title Effects of visual guidance on the reduction of impacts during landings Type Journal Article
  Year 1991 Publication Ergonomics Abbreviated Journal Ergonomics  
  Volume 34 Issue 11 Pages 1399-1406  
  Keywords Adult; Analysis of Variance; Biomechanics; *Cues; Humans; Male; Motor Activity/*physiology; Psychomotor Performance/physiology; Vision, Ocular/*physiology  
  Abstract While a common view is that vision is essential to motor performance, some recent studies have shown that continuous visual guidance may not always be required within certain time constraints. This study investigated a landing-related task (self-released falls) to assess the extent to which visual information enhances the ability to reduce the impacts at touchdown. Six individuals performed six blocked trials from four height categories in semi-counterbalanced order (5-10, 20-25, 60-65, and 90-95 cm) in vision and no-vision conditions randomly assigned. A series of two-way ANOVA with repeated measures were carried out separately on each dependent variable collapsed over six trials. The results indicated that vision during the flight did not produce softer landings. Indeed, in analysing the first peak (PFP) a main effect for visual condition was revealed in that the mean amplitude was slightly higher when vision was available (F(1,5) = 6.57; p less than 0.05), thus implicating higher forces at impact. The results obtained when the time to the first peak (TFP) was applied showed no significant differences between conditions (F(1,5) less than 1). As expected, in all cases, the analyses yielded significant main effects for the height categories factor. It appears that during self-initiated falls in which the environmental cues are known before the event, visual guidance is not necessary in order to adopt a softer landing strategy.  
  Address Research Department, Wingate Institute, Israel  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN (down) 0014-0139 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:1800107 Approved no  
  Call Number Serial 55  
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