Search results for "kinematic"
showing 10 items of 518 documents
Tri-dimensional and triphasic muscle organization of whole-body pointing movements.
2010
Previous kinematic and kinetic studies revealed that, when accomplishing a whole-body pointing task beyond arm's length, a modular and flexible organization could represent a robust solution to control simultaneously target pointing and equilibrium maintenance. Here, we investigated the underlying mechanisms that produce such a coordinative kinematic structure. We monitored the activity of a large number of muscles spread throughout subjects' bodies while they performed pointing movements beyond arm's length, either with or without imposition of postural or pointing constraints. Analyses revealed that muscle signals lied on a tri-dimensional hyper-plane and were temporally organized accordi…
Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory plannin…
2011
International audience; After an exposure to weightlessness, the central nervous system operates under new dynamic and sensory contexts. To find optimal solutions for rapid adaptation, cosmonauts have to decide whether parameters from the world or their body have changed and to estimate their properties. Here, we investigated sensorimotor adaptation after a spaceflight of 10 days. Five cosmonauts performed forward point-to-point arm movements in the sagittal plane 40 days before and 24 and 72 h after the spaceflight. We found that, whereas the shape of hand velocity profiles remained unaffected after the spaceflight, hand path curvature significantly increased 1 day after landing and return…
Effects of movement direction upon kinematic characteristics of vertical arm pointing movements in man
1998
Vertical arm pointing movements in two directions (upwards and downwards), imposing two different loads (unload and 0.5 kg) and speeds (normal and fast) have been studied in six subjects. Movements were recorded using an optoelectronic system. Data analysis concentrated upon finger-tip kinematics. Significant effects of movement direction were recorded upon velocity profiles. The acceleration time, computed relative to total movement time, was greater for downward movements than for upward movements. In contrast however, no effects of load or speed were observed. Movement time was not affected by movement direction or load, for both speeds tested. These results suggest different planning pr…
Human walking along a curved path. I. Body trajectory, segment orientation and the effect of vision.
2003
Task-related characteristics of gait and segment orientation during natural locomotion along a curved path have been described in order to gain insight into the neural organization of walking. The locomotor task implied continuous deviation from straight-ahead, thereby requiring continuous adjustment of body movement to produce and assist turn-related torques. Performance was compared to straight-ahead locomotion. Subjects easily reproduced both trajectories with eyes open (EO). The actual-to-required trajectory difference increased blindfolded (BF), more so during turning. Stride length was unchanged for the outer but decreased for the inner leg. The feet anticipated subsequent body rotati…
Influence of stimulus color on the control of reaching-grasping movements.
2001
This kinematic study aimed to determine whether color is a stimulus property involved in the control of reaching-grasping movements. Subjects reached and grasped a target-object, located either on the right or on the left of the subject's midline. A distractor, placed along the subject's midline, could be randomly presented. The colors, i.e., both chromaticity (red and green stimuli were presented) and lightness, of the target and distractor were varied in experiment 1. Only stimulus lightness and only stimulus chromaticity were varied in experiments 2 and 3, respectively. In experiment 4 subjects matched with their thumb and index finger the size of the target-stimuli presented in experime…
Visual distractors differentially interfere with the reaching and grasping components of prehension movements
1998
In the present study we addressed the issue of how an object is visually isolated from surrounding cues when a reaching-grasping (prehension) movement towards it is planned. Subjects were required to reach and grasp an object presented either alone or with a distractor. In five experiments, different degrees of elaboration of the distractor were induced by varying: (1) the position of the distractor (central or peripheral); (2) the time when the distractor was suppressed (immediately or delayed, with respect to stimulus presentation); and (3) the type of distractor analysis (implicit or explicit). In addition, we tested whether the possible effects of the distractor on reaching-grasping wer…
Modular Control of Pointing beyond Arm's Length
2009
Hand reaching and bipedal equilibrium are two important functions of the human motor behavior. However, how the brain plans goal-oriented actions combining target reaching with equilibrium regulation is not yet clearly understood. An important question is whether postural control and reaching are integrated in one single module or controlled separately. Here, we show that postural control and reaching motor commands are processed by means of a modular and flexible organization. Principal component and correlation analyses between pairs of angles were used to extract global and local coupling during a whole-body pointing beyond arm's length. A low-dimensional organization of the redundant ki…
Language and motor control.
2000
We investigated the possible influence of automatic word reading on processes of visuo-motor transformation. Subjects reached and grasped an object on which the following Italian words were printed: 'VICINO' (near) or 'LONTAN' (far) on an object either near or far from the agent (experiments 1, 2); PICCOLO (small) or 'GRANDE' (large) on either a small or a large object (experiment 4); and 'ALTO' (high) or 'BASSO' (low) on either a high or a low object (experiment 5). The kinematics of the initial phase of reaching-grasping was affected by the meaning of the printed words. Namely, subjects automatically associated the meaning of the word with the corresponding property of the object and acti…
Planning an action.
1997
The motor control of a sequence of two motor acts forming an action was studied in the present experiment. The two analysed motor acts were reaching-grasping an object (first target) and placing it on a second target of the same shape and size (experiment 1). The aim was to determine whether extrinsic properties of the second target (i.e. target distance) could selectively influence the kinematics of reaching and grasping. Distance, position and size of both targets were randomly varied across the experimental session. The kinematics of the initial phase of the first motor act, that is, velocity of reaching and hand shaping of grasping, were influenced by distance of the second target. No k…
Influence of automatic word reading on motor control.
1998
We investigated the possible influence of automatic word reading on processes of visuo-motor transformation. Six subjects were required to reach and grasp a rod on whose visible face the word 'long' or 'short' was printed. Word reading was not explicitly required. In order to induce subjects to visually analyse the object trial by trial, object position and size were randomly varied during the experimental session. The kinematics of the reaching component was affected by word presentation. Peak acceleration, peak velocity, and peak deceleration of arm were higher for the word 'long' with respect to the word 'short'. That is, during the initial movement phase subjects automatically associate…