Mechanisms underlying the generation of averaged modified trajectories

Henis, Ealan; Flash, Tamar

doi:10.1007/s004220050143

Cited by 28 publications

(44 citation statements)

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“…Using this model, he could simulate reaching movements with ®nal accuracy constraints and perturbation of the target position. Some facts, however, speak against this model: it is continuous, which is not consistent with the discrete nature of motions found previously (Langolf et al 1976;Schmidt 1979;Abend et al 1982;Milner et al 1990;Milner 1992); the kinematics of movements with perturbation of the target position are better reproduced with a model where the movement is the superposition of two submovements: one from the start to the ®rst target and the second from the ®rst to the second target (Flash and Henis 1991;Henis and Flash 1995); the analytical calculations are complex and must be completed numerically (Ho 1992); and ®nally, the smoothness of human motion may result to a large extent from muscle mechanics rather than from explicit trajectory control (Krylow and Rymer 1997).…”

Section: Review Of the Literaturementioning

confidence: 64%

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Quantization of human motions and learning of accurate movements

Burdet

Milner

1998

Biological Cybernetics

123

102

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This paper presents a mathematical model for the learning of accurate human arm movements. Its main features are that the movement is the superposition of smooth submovements, the intrinsic deviation of arm movements is considered, visual and kinesthetic feed-back are integrated in the motion control, and the movement duration and accuracy are optimized with practice. This model is consistent with the jerky arm movements of infants, and may explain how the adult motion behavior emerges from the infant behavior. Comparison with measurements of adult movements shows that the kinematics of accurate movements are well predicted by the model.

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Section: Review Of the Literaturementioning

confidence: 64%

“…1). Using these measurements, Milner showed that the movement can be represented well as the superposition of smooth submovements (Milner 1992), as proposed previously by Morasso (1981;Flash and Henis 1991;Henis and Flash 1995). Milner further suggested that these submovements correspond to visual corrections.…”

Section: Review Of the Literaturementioning

confidence: 77%

Quantization of human motions and learning of accurate movements

Burdet

Milner

1998

Biological Cybernetics

123

102

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“…Since it is computationally simpler to plan parts of a complex movement separately and then combine them together using a simple combination rule, such possibilities have been previously explored. It was proposed that curved hand (and eye) motions are composed of elemental motions, and that complex motion sequences might also be composed of simpler motions Flash 1995). The decoupling of the grasp degrees of freedom from the transport degrees of freedom of a single hand was previously proposed for reaching-to-grasp motions ( The motions were normalized to unit duration and unit rotational and translational amplitudes, and averaged over all subjects.…”

Section: Discussionmentioning

confidence: 99%

“…Since the visual processing to locate a target requires 200-300 ms (Keele 1981, Wann et al 1988) and durations of simple movements are 200-400 ms (Henis and Flash 1995), only one or two feedback-based trajectory corrections are possible for such movements. A control strategy based on real-time feedback is therefore unlikely.…”

Section: Trajectory Planning For a Single Handmentioning

confidence: 99%

“…Some of these addressed the generation of single-joint (Hogan 1982) and multi-joint reaching motions in the horizontal (Morasso Uno et al 1989) and vertical Lacquaniti 1981, Atkeson and planes. Questions relating to the generation of more complex motions were also addressed: for example, modified hand (Flash and Henis 1991, Henis and Flash 1995 and eye ) trajectories, and the generation of trajectory sequences ). However, the trajectory planning that is involved in generating motions of two arms physically coupled through a held object has received relatively little attention (Garvin et al 1994, Žefran et al 1995).…”

Section: Introductionmentioning

confidence: 99%

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Two-arm trajectory planning in a manipulation task

Garvin

Žefran

Henis

et al. 1997

Biological Cybernetics

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This paper addresses the trajectory planning problem for a task which requires positioning and orienting an object firmly grasped by two hands at a visually specified goal configuration in the horizontal plane. The motor task involves three degrees of freedom (two translational and one rotational), and the motions of the arms are constrained by the physical coupling through the held object. Experimentally measured trajectories of two arms in the coordinated positioning/orienting task are presented. The hypothesis that the rotational and translational components of motions are decoupled and independently planned is tested. Two explicit mathematical models to account for the kinematic features of the two-arm motions are formulated, and the predictions of the models are compared with the experimental data. Both models extend the minimum-jerk model to the two-arm coordinated motions case. The trajectories predicted by the models were found to be in qualitative agreement with the experimental data. However, neither model could account for the observed configuration dependence of the motions, nor for some of the properties of the measured velocity components of the motions. Our findings support the idea that the rotational and translational components of two-arm motions in the positioning/orienting task are independently planned in extra-personal space, and are further combined in a hierarchical fashion to produce the observed motions. The tested models may serve as a basis for further investigations of issues pertinent to the generation of two-arm trajectories.

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Effects of roll visual motion on online control of arm movement: reaching within a dynamic virtual environment

2008

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Reaching toward a visual target involves the transformation of visual information into appropriate motor commands. Complex movements often occur either while we are moving or when objects in the world move around us, thus changing the spatial relationship between our hand and the space in which we plan to reach. This study investigated whether rotation of a wide field-of-view immersive scene produced by a virtual environment affected online visuomotor control during a double-step reaching task. A total of 20 seated healthy subjects reached for a visual target that remained stationary in space or unpredictably shifted to a second position (either to the right or left of its initial position) with different inter-stimulus intervals. Eleven subjects completed two experiments which were similar except for the duration of the target's appearance. The final target was either visible throughout the entire trial or only for a period of 200 ms. Movements were performed under two visual field conditions: the virtual scene was matched to the subject's head motion or rolled about the line of sight counterclockwise at 130°/s. Nine additional subjects completed a third experiment in which the direction of the rolling scene was manipulated (i.e., clockwise and counterclockwise). Our results showed that while all subjects were able to modify their hand trajectory in response to the target shift with both visual scenes, some of the double-step movements contained a pause prior to modifying trajectory direction. Furthermore, our findings indicated that both the timing and kinematic adjustments of the reach were affected by roll motion of the scene. Both planning and execution of the reach were affected by roll motion. Changes in proportion of trajectory types, and significantly longer pauses that occurred during the reach in the presence of roll motion suggest that background roll motion mainly interfered with the ability to update the visuomotor response to the target displacement. Furthermore, the reaching movement was affected differentially by the direction of roll motion. Subjects demonstrated a stronger effect of visual motion on movements taking place in the direction of visual roll (e.g., leftward movements during counterclockwise roll). Further investigation of the hand path revealed significant changes during roll motion for both the area and Correspondence to: Assaf Y. Dvorkin, a-dvorkin@northwestern.edusasaf@vms.huji.ac.il. shape of the 95% tolerance ellipses that were constructed from the hand position following the main movement termination. These changes corresponded with a hand drift that would suggest that subjects were relying more on proprioceptive information to estimate the arm position in space during roll motion of the visual field. We conclude that both the spatial and temporal kinematics of the reach movement were affected by the motion of the visual field, suggesting interference with the ability to simultaneously process two consecutive stimuli. NIH Public Access

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Mechanisms underlying the generation of averaged modified trajectories

Cited by 28 publications

References 0 publications

Quantization of human motions and learning of accurate movements

Quantization of human motions and learning of accurate movements

Two-arm trajectory planning in a manipulation task

Effects of roll visual motion on online control of arm movement: reaching within a dynamic virtual environment

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