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Biomedical subjects

G Montagne

Publications and source records attributed to G Montagne.

16 recordsLinked to original sources
PubMed2005

A robust solution for dealing with environmental changes in intercepting moving balls.

The authors tested whether a simple model based on the cancellation of the rate of change in bearing angle could account for the behavioral adaptations produced when individuals intercept moving balls while walking. In Experiment 1, the place of arrival of the ball and the angle of approach were varied. In accord with the model, velocity regulations were earlier and more pronounced the larger the angle of approach. In Experiment 2, ball speed unexpectedly changed during a trial, once again highlighting participants' functional velocity adaptations. A direct test of the model on the basis of each individual trial (N = 256) revealed that, on average, 70% of the total variance could be explained. Together, those results confirm the usefulness of such a robust strategy in the control of interceptive tasks.

Adaptation, Psychological↗
PubMed2004

The perceptual control of goal-directed locomotion: a common control architecture for interception and navigation?

Intercepting a moving object while locomoting is a highly complex and demanding ability. Notwithstanding the identification of several informational candidates, the role of perceptual variables in the control process underlying such skills remains an open question. In this study we used a virtual reality set-up for studying locomotor interception of a moving ball. The subject had to walk along a straight path and could freely modify forward velocity, if necessary, in order to intercept-with the head-a ball moving along a straight path that led it to cross the agent's displacement axis. In a series of experiments we manipulated a local (ball size) and a global (focus of expansion) component of the visual flow but also the egocentric orientation of the ball. The experimental observations are well captured by a dynamic model linking the locomotor acceleration to properties of both global flow and egocentric direction. More precisely the changes in locomotor velocity depend on a linear combination of the change in bearing angle and the change in egocentric orientation, allowing the emergence of adaptive behavior under a variety of circumstances. We conclude that the mechanisms underlying the control of different goal-directed locomotion tasks (i.e. steering and interceptive tasks) could share a common architecture.

Acceleration↗
PubMed2002

The visual control of ball interception during human locomotion.

According to the required velocity model, on-line modulations of movement acceleration are performed on the basis of an optically specified difference between required and current behavior. Can this model account for observed displacement regulations in an interceptive task requiring locomotive displacements? In the present study, a virtual reality set-up was coupled to a treadmill. Subjects walking on the treadmill were required to intercept a virtual ball approaching at eye-level by adjusting their velocity, if necessary. While the required velocity model could partially account for displacement regulation late in the interception, it was ineffective to explain early regulations. The possible use of a bearing angle strategy to control displacement regulation and the possible degree of complimentarity of these strategies are discussed.

Humans↗
PubMed2002

Temporal information for spatially constrained locomotion.

How is locomotion adapted to spatial environmental constraints? The control of this everyday behavior is claimed to be based on information that specifies either spatial or temporal properties of the actor-environment system. Although studies on open-loop locomotor pointing (i.e., the positioning of a foot on a target on the floor while walking) agree on the use of spatial information, studies on closed-loop locomotor pointing propose the use of temporal information. Here, we test the hypothesis of closed-loop locomotor pointing based on temporal information, by dissociating spatial and temporal information in a virtual reality setup (virtual environment connected to a treadmill). The results support this hypothesis and shed some light on the type of temporal information that is used. The performed dissociation between spatial and temporal information, however, does not rule out a control based on a continuous updating of spatial information. Therefore, our conclusion on the use of temporal information was moderated.

Adaptation, Physiological↗
PubMed2002

Perception--action coupling model for human locomotor pointing.

How do humans achieve the precise positioning of the feet during walking, for example, to reach the first step of a stairway? We addressed this question at the visuomotor integration level. Based on the optical specification of the required adaptation, a dynamical system model of the visuomotor control of human locomotor pointing was devised for the positioning of a foot on a visible target on the floor during walking. Visuomotor integration consists of directly linking optical information to a motor command that specifically modulates step length in accordance with the ongoing dynamics of locomotor pattern generation. The adaptation of locomotion emerges from a perception-action coupling type of control based on temporal information rather than on feedforward planning of movements. The proposed model reproduces experimental results obtained for human locomotor pointing.

Foot↗
PubMed2001

Spatially constrained locomotion under informational conflict.

This study investigates the informational based that supports intentional adaptation of locomotion to spatial environmental constraints. A virtual reality setup was used to present subjects with targets providing normal as well as abnormal optical expansion during locomotor pointing (i.e. positioning of a foot on a visible target on the floor during walking). The manipulation dissociated two variables providing temporal information about time-to-passage (TTP): TTP(beta alpha) which encompasses target expansion, and TTP(alpha) which is independent of target expansion. While a previous study showed TTP(alpha) to be sufficient, the present results reveal that TTP(beta alpha) may be used when it is available. This finding indicates that both variables play a role that varies according to the circumstances. Furthermore, the present results provide evidence of the operation of a security principle for action in conflicting situations.

Adaptation, Psychological↗
PubMed2001

Rotor synchronization of radiofrequency and gradient pulses in high-resolution magic angle spinning NMR.

We have investigated the extent to which rotor synchronization of radiofrequency pulses leads to spectral improvement in high-resolution magic angle spinning NMR experiments. Several pulse sequences were tested, and the effect was found to be maximal in homonuclear TOCSY spectra. The physicochemical nature of the sample plays a role in the phenomenon, as rotor synchronization allows the refocusing of residual anisotropic interactions. However, even in a liquid sample the effects were visible. Radial inhomogeneities of the radiofrequency field were identified as an important source of the problem.

Magnetic Resonance Spectroscopy↗
PubMed2000

The control of human locomotor pointing under restricted informational conditions.

Since a perception-action coupling type of control (Kugler, P.N. and Turvey, M.T., Information, Natural Law, and Self-Assembly of Rhythmic Movements, Erlbaum, Hillsdale, 1987, 481 pp.) continuously operates during locomotor pointing tasks (e.g. long jumping) (Montagne, G., Cornus, S., Glize, D., Quaine, F. and Laurent, M., A 'perception-action coupling' type of control in long-jumping. J. Motor Behav., (2000) in press), the information sources underlying this control have to be dealt with. Under the assumption that subjects use information about the first-order time remaining before they pass the target, we identify in the literature four different sources of information that specify this physical property. Only one of these sources is inevitably present under all possible environmental conditions containing at least a continuously visible target on the floor. This study aimed to test its sufficiency to perform a locomotor pointing task. The use of a virtual reality set-up permitted us to compare locomotor pointing executed with all four information sources or only with the aforementioned one. The likeness found between those two conditions, as far as the pointing performance and the mode of control are concerned, expresses the evoked sufficiency.

Biomechanical Phenomena↗
PubMed2000

A perception-action coupling type of control in long jumping.

The authors' goal was to identify the control mechanisms used by long jumpers (N = 6) to precisely position their foot at the board. In addition to the intertrial method usually used in previous research, an original method based on a trial-by-trial analysis was also implemented. If the approach to the board in long jumping encompasses two distinct sequences separated by a key step that marks the initiation of visual control, then a trial-by-trial analysis should reveal those sequences, regardless of the amount of adjustment: The step number at which regulation is initiated should be the same irrespective of the amount of adjustment. If, in contrast, a perception-action coupling mechanism operates, then the step number at which regulation is initiated should be a function of the amount of adjustment: A linear relation between those 2 variables should emerge. The results of the present study are compatible with continuous control mechanisms based on a perception-action coupling.

Adult↗
PubMed2000

The study of locomotor pointing in virtual reality: the validation of a test set-up.

The goal of this experiment was to validate an experimental set-up for studying locomotor pointing. The specific and also original element of this set-up was the interactive nature of virtual reality and movement production. This interaction was achieved through the coupling of a treadmill and a Silicon Graphics system. This latter system generated on a screen (3 x 2.3 m) an environmental array that moved according to the action produced by subjects on a treadmill. The task was to place either foot on a spatial target that appeared on the floor in front of the subject's displacement trajectory. We analyzed the step length patterns of subjects approaching these targets, along with the current target-subject relationship. The results are in agreement with a perception-action coupling type of control mechanism that operates continuously as the subject approaches the desired target. Apparently, these findings mirror observations of real-life locomotion, indicating that the present set-up provides a valid and useful tool for examining human locomotion.

Adult↗
PubMed1999

The regulation of externally paced human locomotion in virtual reality.

The goal of the present experiment was to study regulation of human locomotion under externally paced temporal constraints. On a screen placed in front of a treadmill a virtual hallway was projected (Silicon Graphics systems) in which a pair of doors were presented that continuously opened and closed at a rate of 1 Hz. Subjects were attached to a locometer and instructed to regulate walking pace such that the doors were passed correctly. Performance outcome, movement kinematics (stride duration, stride length and synchronization of stride and door cycles) and flow patterns (change in visual angle of door aperture) were used to examine the data. The analysis of the synchronization patterns indicates that stride cycles were not linked to the period of door oscillation. Moreover, results for stride duration reveal that subjects walked at their preferred speed up to the final phase of the approach. This observation is supported by the inspection of the flow patterns, revealing a final increase in variability as a result of regulation. In sum, regulation of locomotion under externally paced temporal constraints seems to generate a specific functional behavior. It appears that regulations are postponed until the final stage of the approach during which adaptations are made according to the requirements of the current situation.

Biomechanical Phenomena↗
PubMed1999

Movement reversals in ball catching.

This study aimed to determine whether the interception of a moving object is achieved by implementing a predictive or a prospective strategy. We examined the kinematics of catching movement in a situation in which the catching hand was constrained to move along a single dimension. In line with predictions based on a prospective strategy, the results obtained indicated that, for the same interception point and the same initial hand position, modification of the spatiotemporal characteristics of the ball's trajectory (via modification of the angle of approach of the ball) gave rise to systematic changes in the kinematics of catching movement. Moreover, the production of movement reversals when the hand was already positioned at the interception point, while in line with the predictions of the prospective strategy formalized by Bootsma et al. (1997), allowed for rejection of a predictive strategy.

Adult↗
PubMed1994

The control and coordination of one-handed catching: the effect of temporal constraints.

The aim of the experiment was to identify the control mechanisms involved in a goal-directed task by manipulating the temporal constraints. Subjects were required to catch, with one hand, table tennis balls projected by a ball-projection machine under five temporal conditions (ball speed ranged from 5.7 to 9 m/s, giving rise to flight times of 550-350 ms). By means of three-dimensional kinematics analysis the following results were obtained, which are some spatio-temporal adaptations of the catching movement to the increase of temporal constraints: (1) a decrease in movement time, (2) an increase in the straightness of the trajectory of the wrist, and (3) a shift backwards of the place of ball-hand contact while (4) the grasping time was kept constant. Moreover, as a result of increasing temporal constraints, the acceleration phase of the transportation component was kept constant while the deceleration phase was progressively decreased and nearly suppressed. Further, an increased correlation of the initial direction of the transportation component with the initial direction of the ball path was found. These findings show some spatio-temporal adaptations of the catching movement when the time available is manipulated. They also support the contention of a shift in the control mechanisms involved in one-handed catching facing different temporal constraints.

Goals↗
PubMed1994

The effects of environmental changes on one-handed catching.

Ball catching involves predicting the time and place of arrival of a mobile object. Visual cues of various kinds may help a ball catcher to perform this task successfully. The aims of the present study were (a) to assess the role of the environment in the spatiotemporal planning of ball-catching movements and (b) to determine what specific cues are actually used for this purpose. In the first experiment described here, subjects' catching performances were compared under four different environmental conditions, namely, normal lighting, ultraviolet light with no background, ultraviolet light with a densely structured background, and ultraviolet light with a sparsely structured background. Our results showed that the sight of the mobile object alone does not provide enough information for a subject to achieve his maximum performance level. Accurately assessing the point of arrival of the ball requires the use of relative visual cues. The environment is also a source of visual cues used to assess the time of arrival of the ball. A second experiment was carried out with a view to determining the exact nature of the visual cues used. Here, the orientation (frontal vs. oblique plane) and the apparent visual angle (6 degrees vs. 42 degrees ) of the background were made to vary. The results of this experiment showed that the orientation of the background affected the percentage of spatial errors produced by the subjects, whereas the apparent visual angle affected the percentage of temporal errors. The relative velocity cue generated by the masking of successive structures in the environment by the oncoming ball seems to have been taking into account in estimating the time of arrival of the ball. This cue seems to be of crucial importance during the 200 ms prior to the time of contact between the ball and the subject's hand. This finding supports the idea that the method used to assess the time to contact may involve velocity information.

Journal Article↗
PubMed1994

[Psychoimmunology and AIDS: a review of the literature].

In recent years, several studies have been carried out concerning the effect of psychosocial factors on the course of infection due to the human immunodeficiency virus (HIV). After summarizing the current status of general knowledge in the field of psychoimmunology, this article reviews the results of studies conducted in regard to HIV. Two conclusions are reached. The first is that current research has not shown psychosocial factors to have any impact on either the immunity status of seropositive patients or the medical complications inherent to AIDS. The second conclusion is that several types of intervention, in particular psychoeducational approaches, stress management programs, and the strengthening of social and family support, give good results where the psychosocial well-being of patients is concerned and should motivate various health professionals to improve the focus of their interventions. Furthermore, significant methodological weaknesses in several indexed studies are noted, and these should be rectified to enable future studies to confirm or correct the present observations.

Acquired Immunodeficiency Syndrome↗