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Liebermann, D. G., Berman, S., Weiss, P. L. T., & Levin, M. F. (2012). Kinematics of reaching movements in a 2-d virtual environment in adults with and without stroke. IEEE Trans Neural Syst Rehabil Eng, 20(6), 778–787.
Abstract: Virtual reality environments are increasingly being used for upper limb rehabilitation in poststroke patients. Our goal was to determine if arm reaching movements made in a 2-D video-capture virtual reality environment are similar to those made in a comparable physical environment. We compared arm and trunk kinematics for reaches made with the right, dominant arm to three targets (14 trials per target) in both environments by 16 adults with right poststroke hemiparesis and by eight healthy age-matched controls. Movement kinematics were recorded with a three-camera optoelectronic system at 100 samples/s. Reaching movements made by both control and stroke subjects were affected by viewing the targets in the video-capture 2-D virtual environment. Movements were slower, shorter, less straight, less accurate and involved smaller ranges of shoulder and elbow joint excursions for target reaches in the virtual environment compared to the physical environment in all subjects. Thus, there was a decrease in the overall movement quality for movements made in the 2-D virtual environment. This suggests that 2-D video-capture virtual reality environments should be used with caution when the goal of the rehabilitation program is to improve the quality of movement patterns of the upper limb.
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Liebermann, D. G., Berman, S., Weingarden H., Levin, M. F., & Weiss, P. L. (2009). Kinematic features of arm and trunk movements in stroke patients and age-matched healthy controls during reaching in virtual and physical environments. In Virtual Rehabilitation International Conference (pp. 179–184).
Abstract: Motor performance of stroke patients and healthy individuals was compared in terms of selected kinematic features of arm and trunk movements while subjects reached for visual targets in virtual (VR) and physical (PH) environments. In PH, the targets were placed at an extended arm distance, while in VR comparably placed virtual targets were presented via GestureTek's IREX system. Our goal was to obtain further insights into research methods related to VR-based rehabilitation. Eight right-hemiparetic stroke patients (age =46-87 years) and 8 healthy adults (age =51-73 years) completed 84 reaching movements in VR and PH environments while seated. The results showed that arm and trunk movements differed in the two environments in patients and to a lesser extent in healthy individuals. Arm motion of patients became jerkier in VR, with larger paths and longer movement durations, and presented greater arm torsion (i.e., larger elbow rotations around the hand-shoulder axis). Interestingly, patients also showed a significant reduction of compensatory trunk movements during VR reaching. The findings indicate that when targets were perceived to be beyond hand reach, stroke patients may be less able to estimate 3D virtual target locations obtained from the 2D TV planar displays. This was not the case for healthy participants.
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Frenkel-Toledo, S., Levin, M. F., Berman, S., Liebermann, D. G., Baniña, M. C., Solomon, J. M., et al. (2022). Shared and distinct voxel-based lesion-symptom mappings for spasticity and impaired movement in the hemiparetic upper limb. Sci Rep, 12(1).
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Krasovsky, T., Berman, S., & Liebermann, D. G. (2010). Kinematic features of continuous hand reaching movements under simple and complex rhythmical constraints. J Electromyogr Kinesiol, 20(4), 636–641.
Abstract: BACKGROUND: Auditory cues are known to alter movement kinematics in healthy people as well as in people with neurological conditions (e.g., Parkinson's disease or stroke). Pacing movement to rhythmical constraints is known to change both the spatial and temporal features of movement. However, the effect of complexity of pacing on the spatial and temporal kinematic properties is still poorly understood. The current study investigated spatial and temporal aspects of movement (path and speed, respectively) and their integration while subjects followed simple isochronous or complex non-isochronous rhythmical constraints. Spatiotemporal decoupling was expected under the latter constraint. METHODS: Ten subjects performed point-to-point hand movements towards visual targets on the surface of a hemisphere, while following continuous auditory cues of different pace and meter. The spatial and temporal properties of movement were compared to geodesic paths and unimodal bell-shaped speed profiles, respectively. Multiple two-way RM-ANOVAs (pace [1-2 Hz] x meter [duple-triple]) were performed on the different kinematic variables calculated to assess hand deviations from the model data (p< or = 0.05). RESULTS: As expected, increasing pace resulted in straighter hand paths and smoother speed profiles. Meter, however, affected only the path (shorter and straighter under triple) without significantly changing speed. Such an effect was observed at the slow pace only. CONCLUSIONS: Under simple rhythmic cues, an increase in pace causes spontaneous adjustments in spatial features (straighter hand paths) while preserving temporal ones (maximally-smoothed hand speeds). Complex rhythmical cues in contrast perturb spatiotemporal coupling and challenge movement control. These results may have important practical implications in motor rehabilitation.
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Liebermann, D. G., Krasovsky, T., & Berman, S. (2008). Planning maximally smooth hand movements constrained to nonplanar workspaces. J Mot Behav, 40(6), 516–531.
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.
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