RESUMO
Bioceramic fabrics have been claimed to improve blood circulation, thermoregulation and muscle relaxation, thereby also improving muscular activity. Here we tested whether bioceramic fabrics have an effect on postural control and contribute to improve postural stability. In Experiment 1, we tested whether bioceramic fabrics contribute to reduce body-sway when maintaining standard standing posture. In Experiment 2, we measured the effect of bioceramic fabrics on body-sway when maintaining a more instable posture, namely a handstand hold. For both experiments, postural oscillations were measured using a force platform with four strain gauges that recorded the displacements of the center of pressure (CoP) in the horizontal plane. In half of the trials, the participants wore a full-body second skin suit containing a bioceramic layer. In the other half of the trials, they wore a 'placebo' second skin suit that had the same cut, appearance and elasticity as the bioceramic suit but did not contain the bioceramic layer. In both experiments, the surface of displacement of the CoP was significantly smaller when participants were wearing the bioceramic suit than when they were wearing the placebo suit. The results suggest that bioceramic fabrics do have an effect on postural control and improve postural stability.
Assuntos
Cerâmica , Vestuário , Ginástica/fisiologia , Equilíbrio Postural/fisiologia , Postura/fisiologia , Adolescente , Adulto , Método Duplo-Cego , Feminino , Humanos , Masculino , Adulto JovemRESUMO
The aim of the present study was to investigate (1) the relative contribution of the egocentric reference as well as body orientation perception to visual horizon percept during tilt or during increased gravito-inertial acceleration (GiA, hypergravity environment) conditions and (2) the role of vestibular signals in the inter-individual differences observed in these perceptual modalities. Perceptual estimates analysis showed that backward tilt induced (1) an elevation of the visual horizon, (2) an elevation of the egocentric estimation (visual straight ahead) and (3) an overestimation of body tilt. The increase in the magnitude of GiA induced (1) a lowering of the apparent horizon, (2) a lowering of the straight ahead and (3) a perception of backward tilt. Overall, visual horizon percept can be expressed as the combination of body orientation perception and egocentric estimation. When assessing otolith reactivity using off-vertical axis rotation (OVAR), only visual egocentric estimation was significantly correlated with horizontal OVAR performance. On the one hand, we found a correlation between a low modulation amplitude of the otolith responses and straight ahead accuracy when the head axis was tilted relative to gravity. On the other hand, the bias of otolith responses was significantly correlated with straight ahead accuracy when subjects were submitted to an increase in the GiA. Thus, straight ahead sense would be dependent to some extent to otolith function. These results are discussed in terms of the contribution of otolith inputs in the overall multimodal integration subtending spatial constancy.
Assuntos
Movimentos Oculares/fisiologia , Gravitação , Individualidade , Orientação/fisiologia , Membrana dos Otólitos/fisiologia , Adulto , Feminino , Humanos , Masculino , Psicofísica , Reflexo Vestíbulo-Ocular , Rotação , Estatística como Assunto , Adulto JovemRESUMO
Perception of body orientation and apparent location of objects are altered when humans are using assisted means of locomotion and the resultant of the imposed acceleration and gravity is no longer aligned with the gravitational vertical. As the otolithic system cannot discriminate the acceleration of gravity from sustained inertial accelerations, individuals would perceive the resultant acceleration vector (GiA) as the vertical. However, when subjects are aligned on the GiA, an increase in the magnitude of GiA induced a lowering of the apparent visual horizon (i.e. "elevator illusion"). The main aim of this study was to quantify the contribution of body and egocentric perception in the elevator illusion. While being exposed to 1G and 1.3G and aligned on the GiA acceleration, subjects (N=20) were asked (1) to set a luminous target to the subjective horizon, (2) to set a luminous target on "straight ahead" position (egocentric task) and (3) to rotate a tilting tube to their subjective perception of body orientation. Results showed that increasing GiA lowered horizon and egocentric settings and induces a backward body tilt perception. Moreover, the elevator illusion can be expressed as the additive combination of two processes: one that is dependent on body tilt perception, and the other that is dependent on egocentric perception. Both misperceptions in hypergravity may be considered to be a consequence of excessive shearing of the otolith organs. However large inter-individual differences in body tilt perception were observed. This last result was discussed in terms of the contribution of extravestibular graviceptors.
Assuntos
Percepção de Movimento , Ilusões Ópticas , Orientação , Postura , Percepção Espacial , Aceleração , Adulto , Centrifugação , Feminino , Humanos , Masculino , Estimulação Luminosa , RotaçãoRESUMO
The nm23 gene family is thought to be involved in physiopathological processes such as growth, differentiation and cancer promotion, progression or metastasis. We report here the mouse nm23-M3 and nm23-M4 complementary DNA sequences and the genomic cloning, characterization and tissue expression pattern of the nm23-M2, nm23-M3 and nm23-M4 genes, in comparison with their human and rat orthologs and with the human nm23-H1 and mouse nm23-M1 genes. The organization and structure of the members of this gene family are remarkably similar in human and rodents. Accordingly, the striking similarities between the human and mouse nm23 genes enable the use of mouse transgenic and knock-out models for studying the role of nucleoside diphosphate kinase isoforms in human physiopathology.
Assuntos
Proteínas Monoméricas de Ligação ao GTP/genética , Núcleosídeo-Difosfato Quinase/genética , Fatores de Transcrição/genética , Sequência de Aminoácidos , Animais , Northern Blotting , Clonagem Molecular , DNA/química , DNA/genética , DNA Complementar/química , DNA Complementar/genética , Embrião de Mamíferos/enzimologia , Embrião de Mamíferos/metabolismo , Éxons , Regulação da Expressão Gênica no Desenvolvimento , Regulação Enzimológica da Expressão Gênica , Genes/genética , Humanos , Hibridização In Situ , Íntrons , Isoenzimas/genética , Camundongos , Dados de Sequência Molecular , Nucleosídeo NM23 Difosfato Quinases , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Alinhamento de Sequência , Análise de Sequência de DNA , Homologia de Sequência de Aminoácidos , Sítio de Iniciação de TranscriçãoRESUMO
This study investigates whether the vertical orientation may be predominantly used as an amodal reference norm by the visual, haptic, and somato-vestibular perceptual systems to define oblique orientations. We examined this question by asking the same sighted adult subjects to reproduce, in the frontal (roll) plane, the vertical (0 degree) and six oblique orientations in three tasks involving different perceptual systems. In the visual task, the subjects adjusted a moveable rod so that it reproduced the orientation of a visual rod seen previously in a dark room. In the haptic task, the blindfolded sighted subjects scanned an oriented rod with one hand and reproduced its orientation, with the same hand, on a moveable response rod. In the somato-vestibular task, the blind-folded sighted subjects, sitting in a rotating chair, adjusted this chair in order to reproduce the tested orientation of their own body. The results showed that similar oblique effects (unsigned angular error difference between six oblique orientations and vertical orientation) were observed across the three tasks. However, there were no positive correlations between the visual, haptic, and somato-vestibular oblique effects. Moreover, in some oblique orientations, there was a tendency to overestimate the angle between the oblique orientation and the vertical orientation. This effect varied according to the orientation value and the modality. Taken together, these findings suggest that although vertical orientation is used as a reference norm in the visual, haptic, and somato-vestibular systems to define oblique orientations, specific processing mechanisms seem to be at work in each perceptual system.
Assuntos
Julgamento/fisiologia , Cinestesia/fisiologia , Percepção Espacial/fisiologia , Tato/fisiologia , Vestíbulo do Labirinto/fisiologia , Percepção Visual/fisiologia , Adulto , Sinais (Psicologia) , Meio Ambiente , Gravitação , Humanos , Masculino , PeriodicidadeRESUMO
Seated observers requested to detect low-velocity passive rotations show a high motion-detection threshold. However, when standing on a slowly rotating platform, their equilibrium is preserved, suggesting that cognitive sensing and sensorimotor reactions do not share the same central processes. The present experiments investigated the ability of observers seated on a slowly rotating chair in total darkness to indicate with their hand the position of briefly flashed targets (Experiment 1) and to indicate the subjective horizon with an outstretched arm (Experiment 2) or with a target driven by a joystick (Experiment 3). The overall hypothesis stated that egocentric coding of the position of a target should not be affected by sensing or not-sensing body rotation (Experiment 1), while geocentric positioning may (Experiments 2 and 3). Our data partially supported the hypothesis. Subjects pointed accurately to the memorized targets (Experiment 1), whereas misperception of body orientation was a source of inaccuracy for actions referred to a geocentric frame (Experiments 2 and 3). More interestingly, subjects' perceptions changed as a single, smooth, and monotonic function of tilt, independent of whether the perception of body orientation was present or not.
Assuntos
Atividade Motora/fisiologia , Movimento/fisiologia , Orientação/fisiologia , Postura , Propriocepção/fisiologia , Desempenho Psicomotor/fisiologia , Adulto , Feminino , Humanos , Masculino , Valores de Referência , Análise de Regressão , RotaçãoRESUMO
The visually perceived eye level (VPEL) has been shown to shift toward the lower part of the body in upright subjects facing toward the axis of rotation on a centrifuge. This shift occurs in the same direction as the shift in the gravito-inertial forces (Gis) produced by very low radial acceleration (centrifugation) combined with gravity. The purpose of this study was to determine whether the same phenomenon affects the visually perceived apparent zenith (VPAZ) in subjects in a supine position. Twelve supine subjects were instructed to set a luminous target to the VPAZ, either while they were in total darkness and motionless or while undergoing very low centrifugation. Data showed that Gis induced a VPAZ shift similar to that observed for the VPEL. Thus, as is the case for the VPEL, the corresponding logarithmic psychophysical function of the VPAZ may be considered to be a type of oculogravic illusion phenomenon with differences in the subjects' that differs from subject to subject, depending on the subject's sensitivity to low radial accelerations. Data on VPEL and VPAZ support the notion that the subjective perception of eye level in total darkness takes into account changes--even if extremely slight-in the direction of the gravito-inertial forces produced by the combination of gravity and low radial accelerations, although subjects are unaware of the Gi shift. However, depending on the intensity of the radial acceleration and the angular deviation of Gi relative to G, the shift of the VPEL and the VPAZ can be either amplified or attenuated. Moreover, differences between VPEL and VPAZ responses suggest two explanatory assumptions--namely, that this is (1) a peripheral phenomenon dependent on the neurophysiological anisotropy of the otolithic system or (2) a central phenomenon dependent on the relevance assigned to the peripheral information by the integrative sensory functions and the associative processes.
Assuntos
Percepção de Movimento , Decúbito Dorsal , Adulto , Gravitação , Humanos , Masculino , Psicofísica , Distribuição AleatóriaRESUMO
We compared the contribution and the effectiveness of modulating the orientation perception of two types of visual information: the visual frame and the visual polarity of objects. In experiment 1, we examined the effect of a square frame, a mouse, an elephant, and a map of France on the apparent vertical. In the upright position, despite the presence of tilted individual component features, the visual objects had no illusory visual tilt effects. When tilted, these objects had a substantial effect on the direction that appeared to be vertical. However, rod-setting errors were smaller in the inducing objects than when observed with the frame display. In the second experiment, the results of experiment 1 were replicated with a meaningful circular contour--a porthole and a clock. The presence of the external circular contour did not abolish the illusion on the apparent vertical. Moreover, in experiment 3, a clock whose numbers were displaced and not tilted--to avoid the possible tilt influence of visual cues--was also able to deflect the subjective visual vertical. This finding suggests that through top-down processing shapes can act as a framework which serves as a reference influencing the perceived orientation of the inner objects.
Assuntos
Cognição/fisiologia , Orientação/fisiologia , Percepção Espacial/fisiologia , Adulto , Análise de Variância , Feminino , Humanos , MasculinoRESUMO
This study investigated the effects of heat exposure, exercise-induced dehydration and fluid ingestion on cognitive performance. Seven healthy men, unacclimatized to heat, were kept euhydrated or were dehydrated by controlled passive exposure to heat (H, two sessions) or by treadmill exercise (E, two sessions) up to a weight loss of 2.8%. On completion of a 1-h recovery period, the subjects drank a solution containing 50 g l(-1) glucose and 1.34 g l(-1) NaCl in a volume of water corresponding to 100% of his body weight loss induced by dehydration. (H1 and E1) or levels of fluid deficit were maintained (H0, E0). In the E0, H0 and control conditions, the subject drank a solution containing the same quantity of glucose diluted in 100 ml of water. Psychological tests were administered 30 min after the dehydration phase and 2 h after fluid ingestion. Both dehydration conditions impaired cognitive abilities (i.e. perceptive discrimination, short-term memory), as well as subjective estimates of fatigue, without any relevant differences between the methods. By 3.5 h after fluid deficit, dehydration (H0 and E0) no longer had any adverse effect, although the subjects felt increasingly tired. Thus, there was no beneficial effect of fluid ingestion (H1 and E1) on the cognitive variables. However, long-term memory retrieval was impaired in both control and dehydration situations, whereas there was no decrement in performance in the fluid ingestion condition (H1, E1).
Assuntos
Cognição/fisiologia , Desidratação/fisiopatologia , Ingestão de Líquidos/fisiologia , Transtornos de Estresse por Calor/fisiopatologia , Esforço Físico/fisiologia , Adulto , Análise de Variância , Cognição/efeitos dos fármacos , Desidratação/psicologia , Exercício Físico/fisiologia , Teste de Esforço/efeitos dos fármacos , Teste de Esforço/psicologia , Glucose/farmacologia , Transtornos de Estresse por Calor/psicologia , Temperatura Alta , Humanos , Masculino , Soluções para Reidratação/farmacologiaRESUMO
This study investigated the effects of hypoxia on parallel/preattentional and serial/attentional processes in early vision, and the use of a positive-end-expiratory-pressure (PEEP) to prevent the impairment in performance. Twenty-one subjects were submitted to an 8-h hypoxia exposure in a hypobaric chamber (4500 m, 589 hPa, 22 degrees C), both with and without a 5-cm H2O PEEP. Subjects carried out a visual search task consisting of detecting a target among distractors in normoxia, in acute and in prolonged hypoxia. Conjointly their sensitivity to acute mountain sickness (AMS) was scored through the Lake Louise AMS scoring system. Results showed that prolonged hypoxia slowed serial/attentional processing whereas parallel/preattentional processes were not impaired either by acute or by prolonged hypoxia. PEEP prevented serial/attentional processes from slowing and those effects were more clearly observed in the AMS sensitive subjects with respect to the AMS insensitive subjects. These results suggest that the slowing induced by prolonged hypoxia is specific to an early visual process that pilots the scanning of an attentional spotlight throughout the visual field.
Assuntos
Doença da Altitude/fisiopatologia , Atenção/fisiologia , Hipóxia/fisiopatologia , Processos Mentais/fisiologia , Respiração com Pressão Positiva , Adulto , Doença da Altitude/complicações , Humanos , Hipóxia/complicações , Masculino , Sensibilidade e EspecificidadeRESUMO
The purpose of this study was to investigate how experts in motor skills requiring a fine postural control perceive their body orientation with few gravity based sensory cues. In Experiment 1, expert gymnasts and controls had to detect their body tilt when pitching at a velocity of 0.05 deg.s(-1), in two conditions of body restriction (strapped and body cast altering the somatosensory cues). Contrary to the experts, the controls exhibited a larger body tilt when totally restrained in the body cast. In Experiment 2, subjects had to estimate their Subjective Postural Vertical (SPV) starting from different angles of pitch tilt. The controls exhibited significant errors of SPV judgement whereas the experts were very precise. These results suggest that 1) somatosensory cues are more informative than otolithic cues for the perception of body orientation, and 2) the efficiency of otolithic and/or interoceptive inputs can be improved through a specific training to compensate for the lack of somatosensory cues.
Assuntos
Ginástica/psicologia , Orientação/fisiologia , Adolescente , Adulto , Sinais (Psicologia) , Escuridão , Feminino , Gravitação , Humanos , Masculino , Postura/fisiologia , Canais Semicirculares/fisiologia , Tato/fisiologiaRESUMO
The purpose of the present experiment was to investigate the extent to which subjects can perceive, at very slow velocities, an angular rotation of the support surface about the medio-lateral axis of the ankle, knee, hip, or neck joint when visual cues are not available. Subjects were passively displaced on a slowly rotating platform at .01, .03, and .05 deg/sec. The subjects' task was to detect movements of the platform in four different postural conditions allowing body oscillations about the ankle, knee, hip, or neck joint. In Experiment 1, subjects had to detect backward and forward rotation (pitching). In Experiment 2, they had to detect left and right rotations of the platform (rolling). In Experiment 3, subjects had to detect both backward/forward and left/right rotations of the platform, with the body fixed and the head either fixed or free to move. Overall, when the body was free to oscillate about the ankle, knee, or hip joints, a similar threshold for movement perception was observed. This threshold was lower for rolling than for pitching. Interestingly, in these postural conditions, an unconscious compensation in the direction opposite to the platform rotation was observed on most trials. The threshold for movement perception was much higher when the head was the only segment free to oscillate about the neck joint. These results suggest that, in static conditions, the otoliths are poor detectors of the direction of gravity forces. They also suggest that accurate perception of body orientation is improved when proprioceptive information can be dynamically integrated.
Assuntos
Limiar Diferencial/fisiologia , Sensação Gravitacional/fisiologia , Articulações/fisiologia , Orientação/fisiologia , Propriocepção/fisiologia , Adulto , Análise de Variância , Feminino , Humanos , Perna (Membro) , Masculino , Percepção de Movimento/fisiologia , Pescoço , Postura/fisiologia , Rotação , Estudos de Tempo e MovimentoRESUMO
The aim of this paper is to demonstrate the presence of a similar visual field effect on both spatial orientation and egocentric localization. A first experiment explored an orientation task (Visually Perceived Vertical or VPV determination) and compared the effects of a frame inclined either in the midfrontal plane (in this condition subjects assessed roll VPV) or in the median plane (subjects assessed pitch VPV) or in both combined planes (subjects assessed both roll and pitch VPV). A second experiment compared the frame effects specified above to the frame effect observed in an egocentric localization task (Visually Perceived Eye Level judgment) performed with a frame slanted in the median plane. The results showed that angular frame variations from -15 to +15 deg result in the same psychometric function for both orientation and localization tasks. In each experiment, correlations showed that individual differences occur in relation to an overall sensitivity to the visual field. Individual sensitivity may be accounted for by a ratio of visual to graviceptive information which remains constant whatever the perception plane (midfrontal or median plane) and whatever the task (spatial orientation or localization).
Assuntos
Orientação/fisiologia , Percepção Espacial/fisiologia , Campos Visuais/fisiologia , Adulto , Feminino , Gravitação , Humanos , Masculino , Variações Dependentes do Observador , Reconhecimento Visual de Modelos/fisiologiaRESUMO
In order to study the processes of central vision in deaf subjects, 12 congenitally deaf adults and 12 normally hearing adults performed a visual search task. The task consisted of detecting a "Q" target among "O" distractors in variable numbers and the reverse. The method used a paradigm based on the stimulus onset asynchrony (SOA) specifically designed to measure the visual processing time between the visual array and a mask. A different visual search pattern was observed in each group. The hearing subjects showed an asymmetrical visual search pattern (parallel versus serial processing respectively for "Q" and "O" targets). In contrast, the deaf subjects showed a symmetrical search pattern (parallel processing in both experimental conditions). In a visual task selectively supported by central vision, visual processes of the congenitally deaf are more efficient when the task involves the contribution of serial processes.
Assuntos
Surdez/congênito , Percepção Visual/fisiologia , Adolescente , Adulto , Análise de Variância , Estudos de Casos e Controles , Computadores , Feminino , Humanos , Masculino , Estimulação Luminosa , Valores de ReferênciaRESUMO
BACKGROUND: Exposure to high altitudes requires acclimation or acclimatization, to prevent the negative effects of severe hypoxia. Among several methods, short acclimation with intermittent exposure to severe hypoxia in a hypobaric chamber triggers efficient physiological pre-adaptation mechanisms (11-13). However, we have little knowledge about the cognitive repercussions of such an acclimation protocol. METHODS: Four mountaineers were tested daily in the course of a short acclimation protocol (5 d). After their SaO2 (arterial oxyhemoglogin saturation) were recorded, they carried out a choice reaction time task (Manikin test) twice every day; first at ground level (250 m, control sessions), second at the highest altitude of the day (D1 = 5000 m, D2 = 5500 m, D3 = 6000 m, D4 = 6500 m, D5 = 7000 m). RESULTS: High altitude SaO2 level decreased during the first 3 d, then stabilized around 72-73%. Despite a slight and transient increase at the highest altitude relative to the ground level in D4, the error rate remained low throughout the protocol. Further, response time to the Manikin task did not show significant changes among the days during the acute stage of hypoxia relative to ground level up to 7000 m. CONCLUSIONS: On the whole, it seems that a short acclimation protocol based on intermittent exposure to simulated high altitudes triggered adaptive processes without major impairment in a choice reaction time task during the acute stages of severe hypoxia.
Assuntos
Aclimatação , Doença da Altitude/prevenção & controle , Cognição , Hipóxia/fisiopatologia , Doença Aguda , Adulto , Gasometria , Humanos , Hipóxia/sangue , Masculino , Testes Neuropsicológicos , Oxiemoglobinas/análise , Desempenho Psicomotor , Tempo de ReaçãoRESUMO
This experiment dealt with the role of strobe frequency on the rod and frame effect in frame-dependent and frame-independent subjects in light of the destabilizing effect of strobe lighting on body posture. Analysis showed that the frame effect was resistant to strobe illumination and was significantly stronger at 2 Hz than at 9 Hz. Since the stroboscopic effect was not related to the extent of the frame effect observed in normal light, there was no over-all dependence on the different components of the visual field (static and kinetic). Moreover, analysis of eye movements during stroboscopic exposure confirmed previous observation of a visual scanning style related to orienting activity.
Assuntos
Luz , Orientação , Postura , Percepção Espacial , Campos Visuais , Adulto , Movimentos Oculares , Feminino , Humanos , Masculino , Periodicidade , Estimulação LuminosaRESUMO
Three experiments were conducted to test the effect of postural information, resulting from the active control of balance, on the perception of the vertical. Subjects were required to adjust a luminous rod in two different visual contexts: in the dark or within a tilted visual frame. In these experiments, postural activity was manipulated by placing observers either in a situation of slight postural imbalance (Experiment 1) or in a situation of postural immobilization (Experiment 2). In both situations performance was compared with a control condition in which subjects were standing upright freely (Experiment 1) or sitting unconstrained (Experiment 2). Results showed no main effect of active posture or of immobilization on the visual perception of the vertical. In the third experiment, subjects were supine with their Z body axis perpendicular to the plane of the luminous rod. Thus, body orientation relative to gravity was modified and motor activity reduced. In this position, the physical vertical was perceived quite accurately in a dark environment. Moreover, in the titled frame condition, the supine body position clearly improved vertical judgements. These results are discussed in relation to the ecological theory of orientation.
Assuntos
Postura , Percepção Espacial , Dimensão Vertical , Humanos , Decúbito DorsalRESUMO
The aim of this study was to determine the diagnostic efficiency of transesophageal echocardiography (TEE) in isthmic aortic ruptures and to describe the echocardiographic Doppler anomalies. TEE was performed prospectively for 18 months in 33 patients with serious polytraumas requiring intensive care. The average age was 40.75 years (range, 17 to 78 years). Single or biplanar TEE was used. In three patients with aortic transection, echocardiography showed an intimal flap thicker than that of dissections. The flaps were torn and retracted on the free edge. It was difficult to distinguish the periaortic hematoma. Doppler imaging showed turbulent flows in several places around the aorta. These flows were especially visible at the beginning of the intimal flap. They were visible on M-mode color imaging during systole and diastole. During diastole, a large color flow was observed in the middle of the aortic lumen. It was turbulent in some places and mimicked the systolic filling of the aorta. These flows create the characteristic "to and fro sign" spectrum of Doppler imaging, usually seen in peripheral false arterial aneurysms. TEE findings were confirmed in two cases by surgery and in one case by aortography. TEE seems to be an effective means of detecting isthmic rupture, with the diagnosis resting on the data obtained from echocardiography and Doppler imaging. A suspected isthmic disruption should be assessed by an emergency TEE and aortography used only for uncertain or complex cases.
Assuntos
Aorta/lesões , Ruptura Aórtica/diagnóstico por imagem , Ecocardiografia Transesofagiana , Adolescente , Adulto , Idoso , Dissecção Aórtica/diagnóstico por imagem , Aneurisma Aórtico/diagnóstico por imagem , Ecocardiografia Doppler , Ecocardiografia Transesofagiana/métodos , Hematoma/diagnóstico por imagem , Humanos , Pessoa de Meia-Idade , Traumatismo Múltiplo , Estudos Prospectivos , Traumatismos Torácicos/diagnóstico por imagemRESUMO
The purpose of this study was to determine how the combined effects of a reference frame and of very low gravito-inertial forces produced by centrifugation affect the visually perceived eye level (VPEL). Twenty subjects were instructed to set a luminous target to the VPEL under various experimental conditions involving two main factors: (1) visual context (frameless, frame centered, frame moved down 50 mm, and frame moved up 50 mm) and (2) gravito-inertial context (motionless, Gi1 = 9.81001 m/sec2 and Gi2 = 9.95 m/sec2). The visual context significantly reduced the lowering of VPEL in darkness as caused by radial acceleration; this confirms the prevailing role of vision versus propriosomesthesis. However, under condition Gi2, there was a significant effect on the VPEL in spite of the presence of the luminous frame; this demonstrates that VPEL processing involves both visual and propriosomesthesic information. Furthermore, the VPEL varied linearly with the vertical shift of the luminous frame for any of the gravito-inertial conditions used in this study, but, under condition Gi2, the VPEL was shifted downward.
Assuntos
Atenção , Área de Dependência-Independência , Cinestesia , Orientação , Propriocepção , Percepção Visual , Aceleração , Adulto , Adaptação à Escuridão , Feminino , Gravitação , Humanos , Masculino , Pessoa de Meia-Idade , Psicofísica , RotaçãoRESUMO
The visual angle subtended by the frame seems to be an important determinant of the contribution of orientation contrast and illusion of self-tilt (ie vection) to the rod-and-frame effect. Indeed, the visuovestibular factor (which produces vection) seems to be predominant in large displays and the contrast effect in small displays. To determine how these two phenomena are combined to account for the rod-and-frame effect, independent estimates of the magnitude of each component in relation to the angular size subtended by the display were examined. Thirty-five observers were exposed to three sets of experimental situations: body-adjustment test (illusion of self-tilt only), the tilt illusion (contrast only) and the rod-and-frame test, each display subtending 7, 12, 28, and 45 deg of visual angle. Results showed that errors recorded in the three situations increased linearly with the angular size. Whatever the size of the frame, both mechanisms, contrast effect (tilt illusion) and illusory effect on self-orientation (body-adjustment test), are always present. However, rod-and-frame errors became greater at a faster rate than the other two effects as the size of teh stimuli became larger. Neither one nor the other independent phenomenen, nor the combined effect could fully account for the rod-and-frame effect whatever the angular size of the apparatus.