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Biomedical subjects

I Israël

Publications and source records attributed to I Israël.

At least 19 recordsLinked to original sources
PubMed2000

Eye deviation during rotation in darkness in trait anxiety: an early expression of perceptual avoidance?

BACKGROUND: Patients with dizziness and patients with panic disorder and agoraphobia share a common symptomatology. Numerous studies have investigated a potential link between anxiety and the vestibular system, but few of them have addressed the specific topic of spatial representation. METHODS: Passive whole-body rotations in the horizontal plane were imposed on two groups of subjects who differed in their level of trait anxiety. Subjects were seated on a mobile robot in darkness. After each passive rotation, subjects were asked to reproduce the stimulus by driving the robot with a joystick and to perform a rotation of the same magnitude. Eye movements were recorded and analyzed. RESULTS: No difference in either perception (accuracy in the reproduction task) or in VOR gain was found between the two groups of subjects. Mean eye deviation, caused by fast phases of the nystagmus, differed in the two groups. It was typically in the anticompensatory direction in the non-anxious group, and in the compensatory direction the anxious group. Such compensatory movement may be explained by an egocentric orientation strategy, that may in turn indicate a lack of interest toward the visual surroundings. CONCLUSIONS: An egocentric strategy for self-orientation exhibited at a level below the threshold of awareness could reveal the existence of a physiological mode of processing leading to agoraphobic avoidance.

Adult↗
PubMed2000

Self-motion perception during a sequence of whole-body rotations in darkeness.

The main aim of this study was to examine how postrotatory effects, induced by passive whole-body rotations in darkness, could alter the perception of motion and eye movements during a subsequent rotation. Perception of angle magnitude was assessed in a reproduction task: blindfolded subjects were first submitted to a passive rotation about the earth-vertical axis on a mobile robot. They were then asked to reproduce this angle by controlling the robot with a joystick. Stimulus rotations ranged from 80 degrees to 340 degrees. Subjects were given one of two delay instructions: after the stimulus, they either had to await the end of postrotatory sensations before starting reproduction (condition free delay, FD), or they had to start immediately after the end of the stimulus rotation (no delay, ND). The delay in FD was used as an incidental measure of the subjective duration of these sensations. Eye movements were recorded with an infrared measuring system (IRIS). Results showed that in both conditions subjects accurately reproduced rotation angles, though they did not reproduce the stimulus dynamics. Peak velocities reached in ND were higher than in FD. This difference suggests that postrotatory effects induced a bias in the perception of angular velocity in the ND condition.

Acceleration↗
PubMed2000

Perception of two-dimensional, simulated ego-motion trajectories from optic flow.

A veridical percept of ego-motion is normally derived from a combination of visual, vestibular, and proprioceptive signals. A previous study showed that blindfolded subjects can accurately perceive passively travelled straight or curved trajectories provided that the orientation of the head remained constant along the trajectory. When they were turned (whole-body, head-fixed) relative to the trajectory, errors occurred. We ask whether vision allows for better path perception in that situation, to correct or complement vestibular perception. Seated, stationary subjects wore a head mounted display showing optic flow stimuli which simulated linear or curvilinear 2D trajectories over a horizontal ground plane. The observer's orientation was either fixed in space, fixed relative to the path, or changed relative to both. After presentation, subjects reproduced the perceived movement with a model vehicle, of which position and orientation were recorded. They tended to correctly perceive ego-rotation (yaw), but they perceive orientation as fixed relative to trajectory or (unlike in the vestibular study) to space. This caused trajectory misperception when body rotation was wrongly attributed to a rotation of the path. Visual perception was very similar to vestibular perception.

Head Movements↗
PubMed1999

Vestibular information contributes to update retinotopic maps.

In order to investigate the contribution of the vestibular system to spatial orientation, we studied memory-guided saccades in three conditions: visual-memory guided saccades (ViC), saccades to the remembered spatiotopic position of a visual target, after whole-body rotation (SVeC) and saccades to the remembered retinotopic position of a visual target, after whole-body rotation (RVeC). Visual feedback presented after each trial allowed eye position correction. The error was larger in SVeC, but the performance improved throughout the experiment (learning) in that condition only. As learning occurred over the first four trials, we omitted these trials from the average computation, and the significant difference between the conditions disappeared. It is concluded that vestibular information does contribute to update the internal spatial representation of visual information when a visual feedback is provided.

Feedback↗
PubMed1999

Replication of passive whole-body linear displacements from inertial cues. Facts and mechanisms.

Using path integration, normal subjects should be able to compute the distance of a traveled path even from the sole inertial sensory input. Blindfolded subjects were submitted to a passive linear forward displacement along 2 to 10 m. Their task was to replicate the traveled distance, still blindfolded, by driving the vehicle they were seated upon using a joystick that controlled linear speed. Subjects replicated both the length and the velocity profile of the passive travel, suggesting that a dynamic record of experienced motion is stored in memory. Even when the replication of passive motion dynamics was made impossible, the subjects could still replicate the displacement. The results are explained by a dynamic feedback model that performs a running comparison between the perceived instantaneous displacement of the ongoing motion and the displacement derived from a spatiotemporal record of perceived passive motion. A multimodal acceleration-related sensory input is transformed into a displacement-related perception through double time-integration.

Adult↗
PubMed1999

Non-specific directional adaptation to asymmetrical visual-vestibular stimulation.

Subjective estimates of passive whole-body rotations in darkness were evaluated before and after exposure to asymmetrical incoherent visual-vestibular stimulation (VVS). Two subjects who showed large capacity for adaptation to symmetrical incoherent VVS were enrolled in the study. Strikingly, after 45 min of asymmetrical left-right VVS, perception of rotation decreased equally for rotations to the right and to the left indicating that the calibration of vestibular sensory input for spatial orientation did not undergo a directional specific control.

Acoustic Stimulation↗
PubMed1998

Shift of the beating field of vestibular nystagmus: an orientation strategy?

We investigated in humans whether the shift of the beating field, which is often observed during vestibular nystagmus, could be related to some strategy of orientation. Eye movements were measured with an infrared system during an experiment on self-motion perception in the dark. Subjects were asked to rotate, by means of a joystick, a mobile robot on which they were seated in order to reproduce a previously imposed passive rotation. We suggest that the shift of the ocular beating field is the manifestation of two different orientation strategies based on allocentric and egocentric reference frames, respectively. It is also proposed that subjects who preferably used the first strategy exhibited large shifts of the beating field, while the others who probably used egocentric memory did not exhibit any shift.

Eye Movements↗
PubMed1998

The vestibulo-ocular reflex and angular displacement perception in darkness in humans: adaptation to a virtual environment.

The vestibulo-ocular reflex (VOR) and angular displacement perception were measured in 25 healthy humans in darkness before and after exposure to incoherent visual-vestibular stimulation (VVS): 45 min of repeated passive 180 degrees whole-body rotations around the vertical axis concurrent with only 90 degrees rotation in a visual virtual square room. Large inter-individual variability was observed for both VOR gain and turning estimates. The individual VOR gains were not correlated with perceived angles of rotation either before or after VVS. After VVS, the angular displacement perception decreased by 24+/-16% while the VOR gain did not change significantly. The results suggest that adaptive plasticity in turning perception and adaptive plasticity in VOR might be independent of one another.

Adaptation, Physiological↗
PubMed1997

The contribution of otoliths and semicircular canals to the perception of two-dimensional passive whole-body motion in humans.

1. Perception of two-dimensional (2-D) whole-body passive motion in the horizontal plane was studied in twelve blindfolded healthy volunteers: pure rotation in place (180 deg), linear motion (4.5 m) and a semicircular trajectory (radius, 1.5 m; angular acceleration, 0.2 rad s-2) were applied in random sequence by means of a remote-controlled robot equipped with a racing-car seat. The seat orientation in the horizontal plane was controlled by the experimenter, independent of the robot trajectory. Thus different degrees of otolith-canal interaction were obtained. The maximal linear acceleration during the semicircular trajectory was 0.1 g; however, the linear acceleration vector was complex as it rotated relative to the subject's head. 2. In the first of two sessions, subjects were instructed to maintain an angular pointer oriented towards a remote (15 m) previously seen target during the passive movements. In the second session they had to make a drawing of the path of the perceived trajectory, after the movement was finished. 3. The results showed that, on average, the movement of the pointer matched the dynamics of the rotatory component of the 2-D motion well. This suggests that, in the range of linear accelerations used in this study, no appreciable influence of otolith input on canal-mediated perception of angular motion occurred. 4. The curvature of the drawn paths was mostly explained by the input to the semicircular canals. Subjects' reconstruction of motion did not account for the directional dynamics of the input to the otoliths occurring during passive motion. 5. This finding proves that reconstructing trajectory in space does not imply a mathematically perfect transformation of the linear and angular motion-related inputs into a Cartesian or polar 2-D representation. Physiological constraints on the interaction between motion direction and change of heading play an important role in motion perception.

Acceleration↗
PubMed1997

Spatial orientation in humans: perception of angular whole-body displacements in two-dimensional trajectories.

Vestibular perception of whole-body passive rotation in the horizontal plane was studied by applying two-dimensional (2D) motion to eight blindfolded healthy volunteers: pure rotations in place, corner-like trajectories and arcs of a circular trajectory were randomly applied by means of a remotely controlled robot. Angles embedded in the 2D trajectories were 45 degrees, 90 degrees, 135 degrees and 180 degrees. Stimulation of semicircular canals was the same for all trajectories but was accompanied by concurrent otolith stimulation during circular motion. Subjects participated in two successive experimental sessions. In the first session they were instructed to use a pointer to reproduce the total angular displacement after the motion (REPRODUCTION); in the second session they had to keep pointing towards a remote (15 m) memorised target during the motion (TRACKING). In REPRODUCTION subjects tended to overestimate their rotation angle by 28 +/- 11% (mean +/- SD). There was no systematic effect of the trajectory. Overestimation also occurred when subjects were required to rotate in darkness by 180 degrees (by controlling a joystick). In TRACKING there was virtually no overestimation (6 +/- 17%) and the movement of the pointer matched the dynamics of angular motion. We conclude that (a) the brain can separate and memorise the angular component of complex 2D motion; however, a large inter-individual variability in estimating its amplitude exists; (b) in the range of linear accelerations used in the study, no appreciable effect of otolith-canal perceptual interaction was shown; (c) angular displacements can be dynamically transformed into matched pointing movements; (d) overestimation seems to be typical of delayed judgements of angular displacement and of self-controlled rotations in place. This could be due to the characteristics of the physiological calibration of the vestibular input.

Humans↗
PubMed1997

Spatial memory and path integration studied by self-driven passive linear displacement. I. Basic properties.

According to path integration, the brain is able to compute the distance of a traveled path. In this research we applied our previously reported method for studying memory of linear distance, a crucial mechanism in path integration; our method is based on the overt reconstruction of a passive transport. Passive transport is a special case of navigation in which no active control is performed. Blindfolded subjects were first asked to travel 2 m forward, in darkness, by driving with a joystick the robot on which they were seated. The results show that all subjects but two undershot this distance, i.e., overestimated their own displacement. Then, subjects were submitted to a passive linear forward displacement along 2, 4, 6, 8, or 10 m, and had to reproduce the same distance, still blindfolded. The results show that the distance of the stimulus was accurately reproduced, as well as stimulus duration, peak velocity, and velocity profile. In this first condition, the imposed velocity profile was triangular and therefore stimulus distance and duration were correlated. In a second condition, it was shown that distance was correctly reproduced also when the information about stimulus duration was kept constant. Here, different velocity profiles were used as stimuli, and most subjects also reproduced the velocity profile. Statistical analyses indicated that distance was not reproduced as a consequence of duration, peak velocity, or velocity profile reproduction, but was uniquely correlated to stimulus distance. The previous hypothesis of a double integration of the otolith signal to provide a distance estimate can explain our results. There was a large discrepancy between the accuracy with which the subjects matched the velocity profiles and that of distance reproduction. It follows that, whereas the dynamics of passive motion are stored and available to further use, distance is independently estimated. It is concluded that vestibular and somatosensory signals excited by passive transport can be used to build a dynamic as well as a static representation of the traveled path. We found a close quantitative similarity between the present findings on distance reproduction and those obtained from active locomotion experiments in which the same paradigm was used. This resemblance suggests that the two types of navigation tasks draw on common physiological processes and extends the relevance of our results to naturally occurring path integration.

Acceleration↗
PubMed1996

Visual and vestibular factors influencing vestibular "navigation".

In order to elucidate the role of the "starting point" in path integration, normal subjects underwent a self-rotational task in a motor-driven turntable rotating around an earth-vertical axis. They were passively rotated ("stimulus") and had to return to the starting point, controlling the direction and velocity of the turntable by means of a joystick ("response"). The test included conditions with an earth-fixed target (EFT) as starting point, shown before the stimulus, and conditions without EFT presentation. The subject's response always took place in total darkness. Subjects succeeded in returning to the starting point in all conditions but were more precise (i.e. had smaller variability of responses) with the EFT than in the other conditions. The larger data scatter (inaccuracy) in these latter tasks was directly related to the return peak velocity, whereas with EFT there was no relationship between amplitude and velocity of the return motion. These results suggest that the presentation of the starting point (the EFT) allows a real time integration to take place, thereby improving accuracy during self-controlled motion in the dark. Five subjects were also tested with the same rotational paradigm in total darkness throughout, but with the head in a different position during stimulus and response motions. Thus, motion detection was performed by different semicircular canals during stimulus and response. The conditions used were head upright during stimulus, hyper-extended backward during response motion, and head backward during stimulus and upright during response motion. It was found that the accuracy during these tasks did not differ from that during stimulus/response motion without change in the upright or backward head position. These data indicate that estimates of trajectory are, within limits, independent of canal plane.

Head↗
PubMed1995

Spatial memory of body linear displacement: what is being stored?

The ability to evaluate traveled distance is common to most animal species. Head trajectory in space is measured on the basis of the converging signals of the visual, vestibular, and somatosensory systems, together with efferent copies of motor commands. Recent evidence from human studies has shown that head trajectory in space can be stored in spatial memory. A fundamental question, however, remains unanswered: How is movement stored? In this study, humans who were asked to reproduce passive linear whole-body displacement distances while blindfolded were also able to reproduce velocity profiles. This finding suggests that a spatiotemporal dynamic pattern of motion is stored and can be retrieved with the use of vestibular and somesthetic cues.

Acceleration↗
PubMed1995

Cortical control of vestibular-guided saccades in man.

Memory-guided saccades, made to a remembered location to which gaze was directed before a passive body rotation (i.e. with a vestibular input), were electro-oculographically recorded in 24 patients with various cortical lesions and in 18 control subjects. Anticipation and latency, direction errors and accuracy of the first saccade, stability of eye position in darkness and final eye position were quantified. Patients were divided into small groups, each with lesions affecting one of the following cortical areas: left or right frontal eye field (FEF), left or right prefrontal cortex (area 46 of Brodmann) (PFC), left supplementary eye field (SEF), left or right posterior parietal cortex (PPC) and right parieto-temporal cortex (PTC). There were some abnormalities in the results of the right FEF group, concerning anticipation, direction errors and latency of the first saccade, but no abnormality in the accuracy of the first saccade or of the final eye position. Results in the left FEF group were normal. Accuracy of the first saccade was impaired in the SEF group, bilaterally. Final eye position was also inaccurate in the SEF group. In both PFC groups, significant and, in general, bilateral abnormalities existed for all tested parameters. Accuracy of the first saccade was impaired in the PTC group, leftwards. In contrast, the results in both PPC groups were not significantly different from those of control subjects. Our results suggest that (i) the PFC is involved in the memorization of saccade goals probably encoded in spatiotopic coordinates; (ii) the SEF, but not the FEF, is involved in the control of accuracy of these vestibular-derived goal-directed saccades; (iii) the PTC (i.e. the vestibular cortex), but not the PPC, is involved in the control of such saccades. Therefore, a cortical network different from that involved in the control of memory-guided saccades made to visual targets, with only the PFC in common, could control vestibular-derived goal-directed saccades.

Adult↗
PubMed1995

Otolithic thresholds influence the perception of passive linear displacement.

The vestibular sensors are the necessary source of information for estimating self-displacement during passive linear transport. Displacement has to be computed from the otolith signal by means of an integration process (path integration), which provides a measure of linear acceleration. However, the onset of self-motion perception is delayed due to perceptual thresholds. We investigated the effect of these thresholds on the estimation of passive displacement. Subjects seated on a linear acceleration device (ESA-SLED) were displaced to their left or right. Two tasks were performed: (1) subjects pressed a button when they perceived self-motion; (2) subjects pressed a button when they thought they had reached a previously seen visual target located above the sled rail. Displacement estimation (task 2) was found to depend upon the acceleration magnitude and on the individual motion perception threshold measured in task 1. The results can be explained by assuming that self-displacement computation starts at the onset of self-motion perception and is initialised by a value that is independent of the amplitude of acceleration, thereby compensating for the displacement information lost due to the thresholds.

Acceleration↗
PubMed1995

Self-rotation estimate about the vertical axis.

The aim of this paper was to examine the accuracy of passive whole-body self-rotation estimate around the earth-vertical (yaw) axis. Subjects were required to reach an imposed angle of +/- 90 degrees, 180 degrees or 360 degrees (outward way), and then to rotate back to the initial position (return way), through passive rotation controlled by the subject, in darkness. During these rotations, only the semi-circular canals were stimulated. On the outward way, subjects were required to elaborate the correct imposed angle, without any external reference. In average, subjects undershot the expected angles on outward way, which suggests an overestimate of self-rotation, and the error increased with increasing expected angle. On the return way, subjects had to rotate back to the starting point, through a path integration process. There was no effect of the imposed angle on the error, and the variability was lower than on the outward way. The data suggests that the subjects could construct the internal representation of a virtual starting point: the initial body position, which became a goal to reach clearer than the outward rotation angle, which the subjects also have defined, in an environment deprived of any external spatial reference.

Adult↗
PubMed1993

Vestibular perception of passive whole-body rotation about horizontal and vertical axes in humans: goal-directed vestibulo-ocular reflex and vestibular memory-contingent saccades.

This study was aimed at complementing the existing knowledge about vestibular perception of self-motion in humans. Both goal-directed vestibulo-ocular reflex and vestibular memory-contingent saccade (VMCS) tasks were used, respectively as concurrent and retrospective magnitude estimators for passive whole-body rotation. Rotations were applied about the earth-vertical and earth-horizontal axes to study the effect of the otolith signal in self-rotation evaluation, and both in yaw and pitch to examine the horizontal and vertical semi-circular canals. Two different magnitudes of constant angular acceleration (50 degrees/s2 and 100 degrees/s2) were used. The main findings were (1) strong correlation between both oculomotor responses of both tasks, (2) greater accuracy with rotations about the earth-vertical than the earth: -horizontal axis, (3) greater accuracy for yaw than for pitch rotations, (4) greater accuracy for high acceleration than for low, and (5) no effect of the delay (2 s or 12 s) in the VMCS task. Adequacy of both tasks as subjective magnitude estimators of vestibular perception of self-motion is discussed.

Adult↗