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Tenenbaum, G.; Kohler, N.; Shraga, S.; Liebermann, D.G.; Lidor, R. |
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Title |
Anticipation and confidence of decisions related to skilled performance |
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1996 |
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Journal of Sport Psychology |
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27 |
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293-307 |
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Abstract |
This study was carried out to examine anticipatory decisions of novice, intermediate, and expert tennis players and the confidence with which these decisions are made by these athletes. Perceived eye-focus was also measured to verify whether it is related to expertise level prior to action execution. Forty-five Australian players, 15 in each skill category, were exposed to 6 temporal occluded film conditions (480, 320, 160 ms prior to racquet-ball contact, at contact, and 160 and 320 ms after contact) in randomized order within 8 tennis strokes. In each condition, after viewing the filmed sequence, they were asked to report the final ball location of the opponent's stroke, how confident they were in this decision, and their perceived eye-focus location during the sequence. Experts and intermediates were superior in anticipatory decisions to their counterparts, only under short exposure durations. Novices showed more confidence than experts and intermediates at the beginning of the sequence, but after 160 and 320 ms of ball-racquet contact, experts were much more confident than novices, and intermediates. Self-reported eye-focus differed substantially with respect to expertise level. While experts attended to several locations prior to ball-racquet contact, intermediate and novice players gazed at one location. After contact, the reverse was evident. The findings are in partial agreement with other studies which have applied the temporal occlusion paradigm to study expert-novice differences in anticipatory skills. |
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59 |
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Author |
Harel Arzi; Tal Krasovsky; Moshe Pritsch; Dario G. Liebermann |
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Title |
Movement control in patients with shoulder instability: a comparison between patients after open surgery and nonoperated patients |
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Journal Article |
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Year |
2014 |
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Journal of Shoulder and Elbow Surgery |
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23 |
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7 |
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982–992 |
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Smoothness; kinesthesis; arm kinematics; shoulder instability; open surgery |
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Background
Open surgery to correct shoulder instability is deemed to facilitate recovery of static and dynamic motor functions. Postoperative assessments focus primarily on static outcomes (e.g., repositioning accuracy). We introduce kinematic measures of arm smoothness to assess shoulder patients after open surgery and compare them with nonoperated patients. Performance among both groups of patients was hypothesized to differ. Postsurgery patients were expected to match healthy controls.
Methods
All participants performed pointing movements with the affected/dominant arm fully extended at fast, preferred, and slow speeds (36 trials per subject). Kinematic data were collected (100 Hz, 3 seconds), and mixed-design analyses of variance (group, speed) were performed with movement time, movement amplitude, acceleration time, and model-observed similarities as dependent variables. Nonparametric tests were performed for number of velocity peaks.
Results
Nonoperated and postsurgery patients showed similarities at preferred and faster movement speeds but not at slower speed. Postsurgery patients were closer to maximally smoothed motion and differed from healthy controls mainly during slow arm movements (closer to maximal smoothness, larger movement amplitude, shorter movement time, and lower number of peaks; i.e., less movement fragmentation).
Conclusions
Arm kinematic analyses suggest that open surgery stabilizes the shoulder but does not necessarily restore normal movement quality. Patients with recurrent anterior shoulder instability (RASI) seem to implement a “safe” but nonadaptive mode of action whereby preplanned stereotypical movements may be executed without depending on feedback. Rehabilitation of RASI patients should focus on restoring feedback-based movement control. Clinical assessment of RASI patients should include higher order kinematic descriptors. |
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74 |
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Uri, O.; Pritsch, M.; Oran, A.; Liebermann, D.G. |
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Upper limb kinematics after arthroscopic and open shoulder stabilization |
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2014 |
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Journal of Shoulder and Elbow Surgery |
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Journal of Shoulder and Elbow Surgery |
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1058-2746 |
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75 |
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Berman, S.; Liebermann, D.G.; McIntyre, J. |
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Title |
Constrained Motion Control on a Hemispherical Surface – Path Planning |
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2014 |
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Journal of Neurophysiology |
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J Neurophysiol |
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111 |
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5 |
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954-968 |
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Constrained motion; geodesics; path planning |
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Surface-constrained motion, i.e., motion constraint by a rigid surface, is commonly found in daily activities. The current work investigates the choice of hand paths constrained to a concave hemispherical surface. To gain insight regarding the paths and their relationship with task dynamics, we simulated various control policies. The simulations demonstrated that following a geodesic path is advantageous not only in terms of path length, but also in terms of motor planning and sensitivity to motor command errors. These stem from the fact that the applied forces lie in a single plane (that of the geodesic path itself). To test whether human subjects indeed follow the geodesic, and to see how such motion compares to other paths, we recorded movements in a virtual haptic-visual environment from eleven healthy subjects. The task was comprised of point-to-point motion between targets at two elevations (30 degrees and 60 degrees ). Three typical choices of paths were observed from a frontal plane projection of the paths: circular arcs, straight lines, and arcs close to the geodesic path for each elevation. Based on the measured hand paths, we applied k-means blind separation to divide the subjects into three groups and compared performance indicators. The analysis confirmed that subjects who followed paths closest to the geodesic produced faster and smoother movements, compared to the others. The 'better' performance reflects the dynamical advantages of following the geodesic path, as shown by the simulations, and may also reflect invariant features of the control policies used to produce such a surface-constrained motion. |
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Ben-Gurion University of the Negev |
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0022-3077 |
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PMID:24259548 |
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72 |
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Lackritz, H.; Parmet, Y.; Frenkel-Toledo, S.; Banina, M.C.; Soroker, N.; Solomon, J.M.; Liebermann, D.G.; Levin, M.F.; Berman, S. |
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Title |
Effect of post-stroke spasticity on voluntary movement of the upper limb |
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Journal Article |
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Year |
2021 |
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Journal of Neuroengineering and Rehabilitation |
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J Neuroeng Rehabil |
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18 |
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1 |
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81 |
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Gaussian mixture model; Hellinger's distance; Hemiparesis; Kinematics; Kullback-Liebler divergence; Spasticity; Stochastic model; Stroke |
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BACKGROUND: Hemiparesis following stroke is often accompanied by spasticity. Spasticity is one factor among the multiple components of the upper motor neuron syndrome that contributes to movement impairment. However, the specific contribution of spasticity is difficult to isolate and quantify. We propose a new method of quantification and evaluation of the impact of spasticity on the quality of movement following stroke. METHODS: Spasticity was assessed using the Tonic Stretch Reflex Threshold (TSRT). TSRT was analyzed in relation to stochastic models of motion to quantify the deviation of the hemiparetic upper limb motion from the normal motion patterns during a reaching task. Specifically, we assessed the impact of spasticity in the elbow flexors on reaching motion patterns using two distinct measures of the 'distance' between pathological and normal movement, (a) the bidirectional Kullback-Liebler divergence (BKLD) and (b) Hellinger's distance (HD). These measures differ in their sensitivity to different confounding variables. Motor impairment was assessed clinically by the Fugl-Meyer assessment scale for the upper extremity (FMA-UE). Forty-two first-event stroke patients in the subacute phase and 13 healthy controls of similar age participated in the study. Elbow motion was analyzed in the context of repeated reach-to-grasp movements towards four differently located targets. Log-BKLD and HD along with movement time, final elbow extension angle, mean elbow velocity, peak elbow velocity, and the number of velocity peaks of the elbow motion were computed. RESULTS: Upper limb kinematics in patients with lower FMA-UE scores (greater impairment) showed greater deviation from normality when the distance between impaired and normal elbow motion was analyzed either with the BKLD or HD measures. The severity of spasticity, reflected by the TSRT, was related to the distance between impaired and normal elbow motion analyzed with either distance measure. Mean elbow velocity differed between targets, however HD was not sensitive to target location. This may point at effects of spasticity on motion quality that go beyond effects on velocity. CONCLUSIONS: The two methods for analyzing pathological movement post-stroke provide new options for studying the relationship between spasticity and movement quality under different spatiotemporal constraints. |
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The Zlotowski Center, Ben-Gurion University of the Negev, Beer-Sheva, Israel. sigalbe@bgu.ac.il |
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1743-0003 |
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PMID:33985543 |
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108 |
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