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Author Biess, A.; Flash, T.; Liebermann, D.G. url  openurl
  Title (up) Riemannian geometric approach to human arm dynamics, movement optimization, and invariance Type Journal Article
  Year 2011 Publication Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics Abbreviated Journal Phys Rev E Stat Nonlin Soft Matter Phys  
  Volume 83 Issue 3 Pt 1 Pages 031927  
  Keywords Arm/*physiology; Biomechanics; Computer Simulation; Humans; Kinetics; Male; Models, Biological; Models, Statistical; Models, Theoretical; *Movement; Psychomotor Performance/*physiology; Range of Motion, Articular/physiology; Reaction Time/physiology; Space Perception/*physiology; Torque  
  Abstract We present a generally covariant formulation of human arm dynamics and optimization principles in Riemannian configuration space. We extend the one-parameter family of mean-squared-derivative (MSD) cost functionals from Euclidean to Riemannian space, and we show that they are mathematically identical to the corresponding dynamic costs when formulated in a Riemannian space equipped with the kinetic energy metric. In particular, we derive the equivalence of the minimum-jerk and minimum-torque change models in this metric space. Solutions of the one-parameter family of MSD variational problems in Riemannian space are given by (reparameterized) geodesic paths, which correspond to movements with least muscular effort. Finally, movement invariants are derived from symmetries of the Riemannian manifold. We argue that the geometrical structure imposed on the arm's configuration space may provide insights into the emerging properties of the movements generated by the motor system.  
  Address Bernstein Center for Computational Neuroscience, DE-37073 Gottingen, Germany. armin@nld.ds.mpg.de  
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  Language English Summary Language Original Title  
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  Series Volume Series Issue Edition  
  ISSN 1539-3755 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:21517543 Approved no  
  Call Number Serial 29  
Permanent link to this record
 

 
Author Friedman, J.; Amiaz, A.; Korman, M. pdf  url
doi  openurl
  Title (up) The online and offline effects of changing movement timing variability during training on a finger-opposition task Type Journal Article
  Year 2022 Publication Scientific Reports Abbreviated Journal Sci Rep  
  Volume 12 Issue 1 Pages 13319  
  Keywords Fingers; Humans; *Learning; *Motor Skills; Movement; Psychomotor Performance; Upper Extremity  
  Abstract In motor learning tasks, there is mixed evidence for whether increased task-relevant variability in early learning stages leads to improved outcomes. One problem is that there may be a connection between skill level and motor variability, such that participants who initially have more variability may also perform worse on the task, so will have more room to improve. To avoid this confound, we experimentally manipulated the amount of movement timing variability (MTV) during training to test whether it improves performance. Based on previous studies showing that most of the improvement in finger-opposition tasks comes from optimizing the relative onset time of the finger movements, we used auditory cues (beeps) to guide the onset times of sequential movements during a training session, and then assessed motor performance after the intervention. Participants were assigned to three groups that either: (a) followed a prescribed random rhythm for their finger touches (Variable MTV), (b) followed a fixed rhythm (Fixed control MTV), or (c) produced the entire sequence following a single beep (Unsupervised control MTV). While the intervention was successful in increasing MTV during training for the Variable group, it did not lead to improved outcomes post-training compared to either control group, and the use of fixed timing led to significantly worse performance compared to the Unsupervised control group. These results suggest that manipulating MTV through auditory cues does not produce greater learning than unconstrained training in motor sequence tasks.  
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  Series Volume Series Issue Edition  
  ISSN 2045-2322 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:35922460; PMCID:PMC9349301 Approved no  
  Call Number Serial 115  
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Author Liebermann, D.G.; Hoffman, J.R. url  doi
openurl 
  Title (up) Timing of preparatory landing responses as a function of availability of optic flow information Type Journal Article
  Year 2005 Publication Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology Abbreviated Journal J Electromyogr Kinesiol  
  Volume 15 Issue 1 Pages 120-130  
  Keywords Adult; Cues; Electromyography; Humans; Male; Movement/physiology; Muscle, Skeletal/*physiology; Posture/physiology; Psychomotor Performance/*physiology; Vision, Ocular/*physiology  
  Abstract This study investigated temporal patterns of EMG activity during self-initiated falls with different optic flow information ('gaze directions'). Onsets of EMG during the flight phase were monitored from five experienced volunteers that completed 72 landings in three gaze directions (downward, mid-range and horizontal) and six heights of fall (10-130 cm). EMG recordings were obtained from the right gastrocnemius, tibialis anterior, biceps femoris and rectus femoris muscles, and used to determine the latency of onset (L(o)) and the perceived time to contact (T(c)). Impacts at touchdown were also monitored using as estimates the major peak of the vertical ground reaction forces (F(max)) normalized to body mass, time to peak (T(max)), peak impulse (I(norm)) normalized to momentum, and rate of change of force (dF(max)/dt). Results showed that L(o) was longer as heights of fall increased, but remained within a narrow time-window at >50 cm landings. No significant differences in L(o) were observed when gaze direction was changed. The relationship between T(c) and flight time followed a linear trend regardless of gaze direction. Gaze direction did not significantly affect the landing impacts. In conclusion, availability of optic flow during landing does not play a major role in triggering the preparatory muscle actions in self-initiated falls. Once a structured landing plan has been acquired, the relevant muscles respond relative to the start of the fall.  
  Address Department of Physical Therapy, Sackler Faculty of Medicine, Stanley Steyer School of Health Professions, University of Tel Aviv, Ramat Aviv, 69978 Tel Aviv, Israel  
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  Series Volume Series Issue Edition  
  ISSN 1050-6411 ISBN Medium  
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  Notes PMID:15642660 Approved no  
  Call Number Serial 39  
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Author Wilf, M.; Korakin, A.; Bahat, Y.; Koren, O.; Galor, N.; Dagan, O.; Wright, W.G.; Friedman, J.; Plotnik, M. url  doi
openurl 
  Title (up) Using virtual reality-based neurocognitive testing and eye tracking to study naturalistic cognitive-motor performance Type Journal Article
  Year 2024 Publication Neuropsychologia Abbreviated Journal Neuropsychologia  
  Volume 194 Issue Pages 108744  
  Keywords Humans; Aged; *Eye-Tracking Technology; Cognition; Executive Function; *Virtual Reality; Aging; Color trails test; Fall risk; Hand kinematics; Pupil; Virtual reality  
  Abstract Natural human behavior arises from continuous interactions between the cognitive and motor domains. However, assessments of cognitive abilities are typically conducted using pen and paper tests, i.e., in isolation from “real life” cognitive-motor behavior and in artificial contexts. In the current study, we aimed to assess cognitive-motor task performance in a more naturalistic setting while recording multiple motor and eye tracking signals. Specifically, we aimed to (i) delineate the contribution of cognitive and motor components to overall task performance and (ii) probe for a link between cognitive-motor performance and pupil size. To that end, we used a virtual reality (VR) adaptation of a well-established neurocognitive test for executive functions, the 'Color Trails Test' (CTT). The VR-CTT involves performing 3D reaching movements to follow a trail of numbered targets. To tease apart the cognitive and motor components of task performance, we included two additional conditions: a condition where participants only used their eyes to perform the CTT task (using an eye tracking device), incurring reduced motor demands, and a condition where participants manually tracked visually-cued targets without numbers on them, incurring reduced cognitive demands. Our results from a group of 30 older adults (>65) showed that reducing cognitive demands shortened completion times more extensively than reducing motor demands. Conditions with higher cognitive demands had longer target search time, as well as decreased movement execution velocity and head-hand coordination. We found larger pupil sizes in the more cognitively demanding conditions, and an inverse correlation between pupil size and completion times across individuals in all task conditions. Lastly, we found a possible link between VR-CTT performance measures and clinical signatures of participants (fallers versus non-fallers). In summary, performance and pupil parameters were mainly dependent on task cognitive load, while maintaining systematic interindividual differences. We suggest that this paradigm opens the possibility for more detailed profiling of individual cognitive-motor performance capabilities in older adults and other at-risk populations.  
  Address Center of Advanced Technologies in Rehabilitation, Sheba Medical Center, Israel; Department of Physiology and Pharmacology, Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel; Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel. Electronic address: Meir.Plotnik@sheba.health.gov.il  
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  Series Volume Series Issue Edition  
  ISSN 0028-3932 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:38072162 Approved no  
  Call Number Serial 123  
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