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1.
J Vestib Res ; 16(3): 93-103, 2006.
Artigo em Inglês | MEDLINE | ID: mdl-17312337

RESUMO

A major issue in motor control studies is to determine whether and how we use spatial frames of reference to organize our spatially oriented behaviors. In previous experiments we showed that simulated body tilt during off-axis rotation affected the performance in verbal localization and manual pointing tasks. It was hypothesized that the observed alterations were at least partly due to a change in the orientation of the egocentric frame of reference, which was indeed centered on the body but aligned with the gravitational vector. The present experiments were designed to test this hypothesis in a situation where no inertial constraints (except the usual gravitational one) exist and where the orientation of the body longitudinal z-axis was not aligned with the direction of the gravity. Eleven subjects were exposed to real static body tilt and were required to verbally localize (experiment 1) and to point as accurately as possible towards (experiment 2) memorized visual targets, in two conditions, Head-Free and Head-Fixed conditions. Results show that the performance was only affected by real body tilt in the localization task performed when the subject's head was tilted relative to the body. Thus, dissociation between gravity and body longitudinal z-axis alone is not responsible for localization nor for pointing errors. Therefore, the egocentric frame of reference seems independent from the orientation of the gravity with regard to body z-axis as expected from our previous studies. Moreover, the use of spatial referentials appears to be less mandatory than expected for pointing movements (motor task) than for localization task (cognitive task).


Assuntos
Cognição/fisiologia , Movimentos da Cabeça/fisiologia , Orientação/fisiologia , Postura , Desempenho Psicomotor , Adulto , Feminino , Humanos , Masculino , Campos Visuais
2.
Exp Brain Res ; 161(4): 432-40, 2005 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-15578170

RESUMO

Spatial orientation is crucial when subjects have to accurately reach memorized visual targets. In previous studies modified gravitoinertial force fields were used to affect the accuracy of pointing movements in complete darkness without visual feedback of the moving limb. Target mislocalization was put forward as one hypothesis to explain this decrease in accuracy of pointing movements. The aim of this study was to test this hypothesis by determining the accuracy of spatial localization of memorized visual targets in a perturbed gravitoinertial force field. As head orientation is involved in localization tasks and carrying relevant sensory systems (visual, vestibular and neck muscle proprioceptive), we also tested the effect of head posture on the accuracy of localization. Subjects (n=10) were seated off-axis on a rotating platform (120 degrees s(-1)) in complete darkness with the head fixed (head-fixed session) or free to move (head-free session). They were required to report verbally the egocentric spatial localization of visual memorized targets. They gave the perceived target location in direction (i.e. left or right) and in amplitude (in centimeters) relative to the direction they thought to be straight ahead. Results showed that the accuracy of visual localization decreased when subjects were exposed to inertial forces. Moreover, subjects localized the memorized visual targets more to the right than their actual position, that was in the direction of the inertial forces. With further analysis, it appeared that this shift of localization was concomitant with a shift of the visual straight ahead (VSA) in the opposite direction. Thus, the modified gravitoinertial force field led to a modification in the orientation of the egocentric reference frame. Furthermore, this shift of localization increased when the head was free to move while the head was tilted in roll toward the center of rotation of the platform and turned in yaw in the same direction. It is concluded that the orientation of the egocentric reference frame was influenced by the gravitoinertial vector.


Assuntos
Gravidade Alterada , Movimentos da Cabeça/fisiologia , Postura/fisiologia , Percepção Espacial/fisiologia , Comportamento Espacial/fisiologia , Adolescente , Adulto , Análise de Variância , Escuridão , Feminino , Humanos , Masculino , Estimulação Luminosa/métodos , Rotação
3.
Neurosci Lett ; 308(2): 103-6, 2001 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-11457570

RESUMO

The purpose of the present experiment was to investigate the effect of vision on postural control following a lower limbs muscular fatigue. Ten adult males were asked to maintain a single leg upright posture as immobile as possible in two conditions of no-fatigue and fatigue of the calf muscles. This muscles fatigue was achieved by standing on the toes until exhaustion. Within a trial, vision was suppressed or reinserted by eyes closure or opening. Center of foot pressure displacements were recorded using a force platform. Results showed that the availability of vision allowed the subjects to immediately cope with the destabilizing effect induced by muscular fatigue.


Assuntos
Adaptação Fisiológica/fisiologia , Perna (Membro)/fisiologia , Fadiga Muscular/fisiologia , Músculo Esquelético/fisiologia , Postura/fisiologia , Desempenho Psicomotor/fisiologia , Visão Ocular/fisiologia , Adulto , Sistema Nervoso Central/fisiologia , Retroalimentação/fisiologia , Humanos , Perna (Membro)/inervação , Masculino , Músculo Esquelético/inervação , Propriocepção/fisiologia , Vias Visuais/fisiologia , Suporte de Carga/fisiologia
4.
Neurosci Lett ; 303(2): 83-6, 2001 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-11311498

RESUMO

The goal of this paper was (1) to investigate if gymnasts have a more stable standing posture than experts in other sports, and (2) to determine how much gymnasts are affected by the removal of vision in different postural tasks. Six expert gymnasts and six experts in other non-gymnastic sports were asked to maintain balance in three standing postures of increasing difficulty: bipedal, unipedal, and unipedal + unstable support (i.e. 7 cm thick foam surface). Each posture was tested successively with and without vision. Based on the displacement of the center of pressure (range and mean average speed), the results showed that when visual cues were available, postural sway increased with the difficulty of the task, but both groups had comparable performance in all the tasks. When vision was removed, although both groups demonstrated larger postural sway in the unipedal tasks, this effect was less accentuated for the gymnasts. We concluded that gymnasts are able to use the remaining sensory modalities to compensate for the lack of vision in unstable postures.


Assuntos
Ginástica/fisiologia , Destreza Motora/fisiologia , Movimento/fisiologia , Aptidão Física/fisiologia , Equilíbrio Postural/fisiologia , Postura/fisiologia , Percepção Espacial/fisiologia , Adulto , Sinais (Psicologia) , Humanos , Masculino , Estimulação Luminosa
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