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Biomedical subjects

A Berthoz

Publications and source records attributed to A Berthoz.

210 records · Page 12Linked to original sources
PubMedDate not supplied

Influence of graviceptives cues at different level of visual information processing: the effect of prolonged weightlessness.

We evaluated the influence of prolonged weightlessness on the performance of visual tasks in the course of the Russian-French missions ANTARES, Post-ANTARES and ALTAIR aboard the MIR station. Eight cosmonauts were subjects in two experiments executed pre-flight, in-flight and post-flight sessions. In the first experiment, cosmonauts performed a task of symmetry detection in 2-D polygons. The results indicate that this detection is locked in a head retinal reference frame rather than in an environmentally defined one as meridional orientations of symmetry axis (vertical and horizontal) elicited faster response times than oblique ones. However, in weightlessness the saliency of a retinally vertical axis of symmetry is no longer significantly different from an horizontal axis. In the second experiment, cosmonauts performed a mental rotation task in which they judged whether two 3-D objects presented in different orientations were identical. Performance on this task is basically identical in weightlessness and normal gravity.

Aerospace Medicine↗
PubMedDate not supplied

Internal reference frames for representation and storage of visual information: the role of gravity.

Experimental studies of visual mechanisms suggests that the CNS represents image information with respect to preferred horizontal and vertical axes, as shown by a phenomenon known as the "oblique effect". In the current study we used this effect to evaluate the influence of gravity on the representation and storage of visual orientation information. Subjects performed a psychophysical task in which a visually-presented stimulus line was aligned with the remembered orientation of a reference stimulus line presented moments before. The experiments were made on 5 cosmonauts during orbital space flight and additionally on 13 subjects in conditions of normal gravity with a tilting chair. Data were analyzed with respect to response variability and timing. On earth, these measurements for this task show a distinct preference for horizontally and vertically oriented stimuli when the body and gravitational axes were aligned. This preference was markedly decreased or disappeared when the body axis was tilted with respect to gravity; this effect was not connected with ocular counter-rolling nor could we find a preference of any other intermediate axis between the gravity and body aligned axes. On the other hand, the preference for vertical and horizontal axes was maintained for tests performed in microgravity over the course of a 6 month flight, starting from flight day 6. We concluded that subjects normally process visual orientation information in a multi-modal reference frame that combines both proprioceptive and gravitational cues when both are available, but that a proprioceptive reference frame is sufficient for this task in the absence of gravity after a short period of adaptation. Some of the results from this study have been previously published in a preliminary report. Grant numbers: 99-04-48450.

Adult↗
PubMedDate not supplied

Does gravity play an essential role in the asymmetrical visual perception of vertical and horizontal line length?

The eye perceives the length of vertical and horizontal lines with an inherent asymmetry. A vertical line having the same length as a horizontal one is usually perceived to be longer. In this experimental investigation we tested the hypothesis that gravity has a direct role in producing the observed perceptual asymmetry. To this end we performed experiments in weightlessness during long-orbital space flights onboard the MIR station. Subjects performed a psychophysical task in which the length of a visually-presented vertical line was adjusted to match the length of a horizontal reference. On Earth, almost all subjects produce errors in adjusting the length of the vertical line, consistently under-estimating the length of the horizontal reference. The asymmetry of perception of the line lengths persisted in weightlessness. From these results we conclude that the phenomena of asymmetry of perception of the lengths of vertical and horizontal lines is not dependent on gravity, but is instead defined by properties of the system of internal representation. Grant numbers: 99-04-48450.

Adaptation, Physiological↗
PubMedDate not supplied

The Kinelite Project: a new powerful motion analyser for Spacelab and space station.

The goal of the Kinelite Project is to develop a space qualified motion analysis system to be used in space by the scientific community, mainly to support neuroscience protocols. The measurement principle of the Kinelite is to determine, by triangulation mean, the 3D position of small, lightweight, reflective markers positioned at the different points of interest. The scene is illuminated by Infra Red flashes and the reflected light is acquired by up to 8 precalibrated and synchronized CCD cameras. The main characteristics of the system are: Camera field of view: 45 degrees; Number of cameras: 2 to 8; Acquisition frequency: 25, 50, 100, or 200 Hz; CCD format: 256 x 256; Number of markers: up to 64; 3D accuracy: 2mm; Main dimensions: 45 cm x 45 cm x 30 cm; Mass: 23 kg; Power consumption: less than 200 W. The Kinelite will first fly aboard the NASA Spacelab; it will be used, during the NEUROLAB mission (4/98), to support the "Frames of References and Internal Models" (Principal Investigator: Pr. A. Berthoz, Co Investigators: J. McIntyre, F. Lacquaniti).

Aerospace Medicine↗
PubMedDate not supplied

Adaptation as a sensorial profile in trait anxiety: a study with virtual reality.

Twenty-four volunteers were recruited on the basis of their trait anxiety scores (low trait anxiety [LTA] and high trait anxiety [HTA]) as assessed by the State-Trait Anxiety Inventory. Adaptation to conflicting visual-vestibular stimulation (VVS) was used to study integration of space-related multi-sensory information in trait anxiety. First, vestibular perception was assessed by rotating the blindfolded subjects about the vertical axis (horizontal plane rotations) on a remote-controlled mobile robot. The subjects were asked to indicate the perceived rotation by use of an angular pointer. Subjects were then immersed into the center of a visual virtual square room by means of a head-mounted display. They were asked to control the robot with a joystick in order to perform 90 degrees rotations in the virtual room. However, a gain of 0.5 was introduced between visual scene and robot rotation so that the subjects were submitted to a conflict situation in which the 90 degrees rotational visual input was concurrent with a 180 degrees vestibular input. After 45 min of training with the virtual reality display, subjects were tested again in total darkness in order to determine whether their vestibular system had been reset by the conflicting visual signals. We found significant differences in adaptation to VVS between HTA and LTA groups as well as between males and females. Subjects of the HTA group demonstrated larger adaptation than that of the LTA group. Males also showed a greater level of adaptation compared to females. Our results suggest greater visual dependence in HTA subjects. This might be important for understanding the mechanisms underlying pathological anxiety and particularly agoraphobia.

Adult↗
PubMedDate not supplied

An anatomical landmark for the supplementary eye fields in human revealed with functional magnetic resonance imaging.

Together with the frontal and parietal eye fields, the supplementary eye field (SEF) is involved in the performance and control of voluntary and reflexive saccades and of ocular pursuit. This region was first described in non-human primates and is rather well localized on the dorsal surface of the medial frontal cortex. In humans the site of the SEF is still ill-defined. Functional imaging techniques have allowed investigation of the location and function of the SEF. However, there is great variability with regard to the published standardized coordinates of this area. We used here the spatial precision of functional magnetic resonance imaging (fMRI) in order to better localize the SEF in individuals. We identified as the SEF a region on the medial wall that was significantly activated when subjects executed self-paced horizontal saccades in darkness as compared to rest. This region appeared to be predominantly activated in the left hemisphere. We found that, despite a discrepancy of >2 cm found in the standardized Talairach coordinates, the location of this SEF-region could be precisely and reliably described by referring to a sulcal landmark found in each individual: the upper part of the paracentral sulcus.

Adult↗
PubMedDate not supplied

Action of alcohol on vestibular compensation and habituation in the cat.

Several effects of alcohol on vestibular nystagmus are well known, including positional alcoholic nystagmus, a depressive effect on post-rotatory nystagmus, and an inhibition of visual fixation. This study concerns the influence of alcohol on central vestibular compensatory phenomena. In one experiment, hemilabyrinthectomized cats were allowed to compensate for the postoperative spontaneous nystagmus and directional preponderance of post-rotatory nystagmus. Following alcohol injection, spontaneous nystagmus reappeared toward the intact side, positional nystagmus was unidirectional, and post-rotatory nystagmus was profoundly more depressed than for normals. Normal cats subjected to repeated accelerations showed less habituation of post-rotatory nystagmus with alcohol than without.

Animals↗
PubMedDate not supplied

Cross-coupling between horizontal and vertical eye movements during optokinetic nystagmus and optokinetic afternystagmus elicited in microgravity.

The occurrence of horizontal jerks with larger amplitudes than on Earth was observed during vertical optokinetic nystagmus in astronauts tested throughout a 7-day spaceflight. During early exposure to microgravity, a horizontal spontaneous-like nystagmus was recorded in darkness following both vertical and horizontal optokinetic stimulation. In addition, the time constant of vertical OKAN with slow phase up was larger than on the ground. These effects disappeared on flight day 2. Then, the horizontal and vertical OKAN time constants decreased, and gradually returned to the preflight values, as previously observed with the gain of the vestibulo-ocular reflex. The early changes in microgravity are in agreement with those obtained on Earth in monkeys and humans during static tilt relative to gravity. Our findings suggest that the absence of otolithic input in microgravity may have an effect on the optokinetic system which could be mediated by the velocity storage mechanism.

Eye Movements↗
PubMedDate not supplied

Model of coupled or dissociated eye-head coordination.

Tight coupling between eye and head movements have been observed in response to a single visual target offset or a single flash. On this basis, when the visual stimulus consists of two successive steps or flashes in the same (horizontal) direction, either increasing in eccentricity or decreasing in eccentricity, gaze should be due to concomitant eye and head angular displacement. The main findings were that in response to increasing eccentricity stimulus, the majority of the gaze movement had a staircase pattern, and to decreasing eccentricity stimulus, a pulse-step pattern. Some responses were one gaze movement to the final target (or flash) offset. In all these responses, eye and head were tightly coupled. In some cases, however, in response to two flashes or two successive steps decreasing in eccentricity, the initial eye and head movements were dissociated: eye and head were directed to different offsets. Current eye-head models assume a strong coupling between the head displacement and the eye saccade. We have modified the Laurutis and Robinson model to accommodate the new findings of saccade-VOR cooperation and eye-head dissociated responses. we suggest that when gaze falls short of the target offset, the retinal error signal is not only fed to the saccadic system but also partially suppresses the VOR gain control. This allows for "corrective VOR" movements after the gaze saccade has occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗