Journal of Vestibular Research - Volume 13, issue 4-6

Authors: Jaekl, P. | Jenkin, M. | Harris, L.R.

Article Type: Research Article

Abstract: We measured how much the visual world could be moved during various head rotations and translations and still be perceived as visually stable. Using this as a monitor of how well subjects know about their own movement, we compared performance in different directions relative to gravity. For head rotations, we compared the range of visual motion judged compatible with a stable environment while rotating around an axis orthogonal to gravity (where rotation created a rotating gravity vector across the otolith macula), with judgements made when rotation was around an earth-vertical axis. For translations, we compared the corresponding range of visual …motion when translation was parallel to gravity (when imposed accelerations added to or subtracted from gravity), with translations orthogonal to gravity. Ten subjects wore a head-mounted display and made active head movements at 0.5 Hz that were monitored by a low-latency mechanical tracker. Subjects adjusted the ratio between head and image motion until the display appeared perceptually stable. For neither rotation nor translation were there any differences in judgements of perceptual stability that depended on the direction of the movement with respect to the direction of gravity. Show more

DOI: 10.3233/VES-2003-134-611

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 265-271, 2003

Authors: Vidal, Manuel | Lipshits, Mark | McIntyre, Joseph | Berthoz, Alain

Article Type: Research Article

Abstract: In order to bring new insights into the processing of 3D spatial information, we conducted experiments on the capacity of human subjects to memorize 3D-structured environments, such as buildings with several floors or the potentially complex 3D structure of an orbital space station. We had subjects move passively in one of two different exploration modes, through a visual virtual environment that consisted of a series of connected tunnels. In upright displacement, self-rotation when going around corners in the tunnels was limited to yaw rotations. For horizontal translations, subjects faced forward in the direction of motion. When moving up or down …through vertical segments of the 3D tunnels, however, subjects facing the tunnel wall, remaining upright as if moving up and down in a glass elevator. In the unconstrained displacement mode, subjects would appear to climb or dive face-forward when moving vertically; thus, in this mode subjects could experience visual flow consistent with rotations about any of the 3 canonical axes. In a previous experiment, subjects were asked to determine whether a static, outside view of a test tunnel corresponded or not to the tunnel through which they had just passed. Results showed that performance was better on this task for the upright than for the unconstrained displacement mode; i.e. when subjects remained "upright" with respect to the virtual environment as defined by subject's posture in the first segment. This effect suggests that gravity may provide a key reference frame used in the shift between egocentric and allocentric representations of the 3D virtual world. To check whether it is the polarizing effects of gravity that leads to the favoring of the upright displacement mode, the experimental paradigm was adapted for orbital flight and performed by cosmonauts onboard the International Space Station. For these flight experiments the previous recognition task was replaced by a computerized reconstruction task, which proved to be more efficient in terms of the time required to achieve reliable results. Suppressing gravity did not immediately affect relative performance between the two modes, indicating that on-line graviceptor information is not directly responsible for this differential effect. Trends in the evolution of responses over the course of a 10-day mission, however, suggest that human subjects might adapt their ability to represent internally complex 3D displacements. Show more

Keywords: gravity, orbital flight, spatial memory, human, 3D-maze, virtual reality

DOI: 10.3233/VES-2003-134-612

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 273-286, 2003

Authors: Jenkin, H.L. | Dyde, R.T. | Jenkin, M.R. | Howard, I.P. | Harris, L.R.

Article Type: Research Article

Abstract: Perceiving a direction as “up” is fundamental to human performance and perception. Astronauts in microgravity frequently experience reorientation illusions in which they, or their world, appear to flip and ‘up’ becomes arbitrarily redefined. This paper assesses the relative importance of visual cues in determining the perceived up direction. In the absence of information about the origin of illumination, people interpret surface structure by assuming that the direction of illumination is from above. Here we exploit this phenomenon to measure the influence of head and body orientation, gravity and visual cues on the perceived up direction. Fifteen subjects judged the shape …of shaded circles presented in various orientations. The circles were shaded in such a way that when the shading was compatible with light coming from above, the circle appeared as a convex hemisphere. Therefore, by finding which shaded circle appeared most convex, we can deduce the direction regarded as “up”. The different cues contributing to this percept were separated by varying both the orientation of the subject and the surrounding room relative to gravity. The relative significance of each cue may be of use in spacecraft interior design to help reduce the incidence of visual reorientation illusions. Show more

DOI: 10.3233/VES-2003-134-613

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 287-293, 2003

Authors: Young, Laurence R.

Article Type: Research Article

Abstract: Dynamic models have played a more prominent role in the vestibular and oculomotor field than in any other branch of physiology. The ease of identification of input and output variables and the challenge of multi-loop, multi-axis adaptive control has attracted numerous modelers from engineering and shaped behavioral and neurophysiological experimental programs. In particular, the adaptive characteristics of the neurovestibular system have generated continuing speculation as to mechanisms. This treatment of adaptation and multi-sensor integration covers the development and application of such models, principally in the author's laboratory. It emphasizes the continuing relevance of both "model reference" and "error pattern recognition" …notions of adaptive control. Show more

Keywords: vestibular, oculomotor, adaptive, model

DOI: 10.3233/VES-2003-134-614

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 297-307, 2003

Authors: Merfeld, Daniel M.

Article Type: Research Article

Abstract: Normally, the nervous system must process ambiguous graviceptor (e.g., otolith) cues to estimate tilt and translation. The neural processes that help perform these estimation processes must adapt upon exposure to weightlessness and readapt upon return to Earth. In this paper we present a review of evidence supporting a new hypothesis that explains some aspects of these adaptive processes. This hypothesis, which we label the rotation otolith tilt-translation reinterpretation (ROTTR) hypothesis, suggests that the neural processes resulting in spaceflight adaptation include deterioration in the ability of the nervous system to use rotational cues to help accurately estimate the relative orientation of …gravity ("tilt"). Changes in the ability to estimate gravity then also influence the ability of the nervous system to estimate linear acceleration ("translation"). We explicitly hypothesize that such changes in the ability to estimate "tilt" and "translation" will be measurable upon return to Earth and will, at least partially, explain the disorientation experienced when astronauts return to Earth. In this paper, we present the details and implications of ROTTR, review data related to ROTTR, and discuss the relationship of ROTTR to the influential otolith tilt-translation reinterpretation (OTTR) hypothesis as well as discuss the distinct differences between ROTTR and OTTR. Show more

Keywords: spaceflight, adaptation, vestibular, otolith organs, neurovestibular

DOI: 10.3233/VES-2003-134-615

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 309-320, 2003

Authors: Lackner, James R. | DiZio, Paul A.

Article Type: Research Article

Abstract: A series of pioneering experiments on adaptation to rotating artificial gravity environments was conducted in the 1960s. The results of these experiments led to the general belief that humans with normal vestibular function would not be able to adapt to rotating environments with angular velocities above 3 or 4 rpm. By contrast, our recent work has shown that sensory-motor adaptation to 10~rpm can be achieved relatively easily and quickly if subjects make the same movement repeatedly. This repetition allows the nervous system to gauge how the Coriolis forces generated by movements in a rotating reference frame are deflecting movement paths …and endpoints and to institute corrective adaptations. Independent mechanisms appear to underlie restoration of straight movement paths and of accurate movement endpoints. Control of head movements involves adaptation of vestibulo-collic and vestibulo-spinal mechanisms as well as adaptation to motor control of the head as an inertial mass. The vestibular adaptation has a long time constant and the motor adaptation a short one. Surprisingly, Coriolis forces generated by natural turning and reaching movements in our normal environment are typically larger than those elicited in rotating artificial gravity environments. They are not recognized as such because self-generated Coriolis forces during voluntary trunk rotation are perceptually transparent. After adaptation to a rotating environment is complete, the Coriolis forces generated by movements within it also become transparent and are not felt although they are still present. Show more

Keywords: artificial gravity, Coriolis forces, adaptation, movement control, vestibular function

DOI: 10.3233/VES-2003-134-616

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 321-330, 2003

Authors: Parker, Donald E.

Article Type: Research Article

Abstract: Preparation for extended travel by astronauts within the Solar System, including a possible manned mission to Mars, requires more complete understanding of adaptation to altered inertial environments. Improved understanding is needed to support development and evaluation of interventions to facilitate adaptations during transitions between those environments. Travel to another planet escalates the adaptive challenge because astronauts will experience prolonged exposure to microgravity before encountering a novel gravitational environment. This challenge would have to be met without ground support at the landing site. Evaluation of current adaptive status as well as intervention efficacy can be performed using perceptual, eye movement …and postural measures. Due to discrepancies of adaptation magnitude and time-course among these measures, complete understanding of adaptation processes, as well as intervention evaluation, requires examination of all three. Previous research and theory that provide models for comprehending adaptation to altered inertial environments are briefly examined. Reports from astronauts of selected pre- in- and postflight self-motion illusions are described. The currently controversial tilt-translation reinterpretation hypothesis is reviewed and possible resolutions to the controversy are proposed. Finally, based on apparent gaps in our current knowledge, further research is proposed to achieve a more complete understanding of adaptation as well as to develop effective counter-measures. Show more

Keywords: vestibular receptors, space flight, perception, self-motion, illusions

DOI: 10.3233/VES-2003-134-617

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 331-343, 2003

Authors: Shelhamer, Mark | Zee, David S.

Article Type: Research Article

Abstract: It has been demonstrated that various vestibular and oculomotor responses can be adapted in a context-specific manner: different adapted states are associated with different states of a prevailing context cue, and a change in the context state triggers a change in the response such that each adapted state is associated with a given context state. We review selected literature on context-specific adaptation, including our own recent results on adaptation of saccades, pursuit, and the linear and angular vestibulo-ocular reflexes (LVOR and AVOR), and suggest some ways in which context-specific adaptation might be useful as a countermeasure to the adverse neurovestibular …effects of space flight. Show more

DOI: 10.3233/VES-2003-134-618

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 345-362, 2003

Authors: Watt, Douglas | Lefebvre, Luc

Article Type: Research Article

Abstract: Normal movements performed while voluntarily fixing the head to the torso can lead to motion sickness in susceptible individuals. The underlying mechanism may involve excessive suppression of vestibular responses. A similar motor strategy is often adopted in the early days of a space flight and might contribute to the development of space motion sickness. In a recent experiment, we monitored the eye, head and upper torso rotations of four Life and Microgravity Spacelab crew members. For the purposes of this study, all data were excluded except for periods during which the subject was performing pure yaw-axis head movements. All …subjects showed a significant increase in gaze slip on the first day of their mission, suggesting that increased vestibular suppression was occurring. Furthermore, this amount of increased suppression would have been more than adequate to produce motion sickness in susceptible individuals on the ground. The results support the theory of two, independent mechanisms for space motion sickness. Show more

Keywords: vestibular system, vestibular suppression, motion sickness, space flight, gaze stability

DOI: 10.3233/VES-2003-134-619

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 363-376, 2003

Authors: Moore, Steven T. | Clément, Gilles | Dai, Mingjai | Raphan, Theodore | Solomon, David | Cohen, Bernard

Article Type: Research Article

Abstract: In this paper we review space flight experiments performed by our laboratory. Rhesus monkeys were tested before and after 12 days in orbit on COSMOS flights 2044 (1989) and 2229 (1992–1993). There was a long-lasting decrease in post-flight ocular counter-rolling (70%) and vergence (50%) during off-vertical axis rotation. In one animal, the orientation of optokinetic after-nystagmus shifted by 28° from the spatial vertical towards the body vertical early post-flight. Otolith-ocular and perceptual responses were also studied in four astronauts on the 17-day Neurolab shuttle mission (STS-90) in 1998. Ocular counter-rolling was unchanged in response to 1-g and 0.5-g Gy centrifugation …during and after flight and to post-flight static roll tilts relative to pre-flight values. Orientation of the optokinetic nystagmus eye velocity axis to gravito-inertial acceleration (GIA) during centrifugation was also unaltered by exposure to microgravity. Perceptual orientation to the GIA was maintained in-flight, and subjects did not report sensation of translation during constant velocity centrifugation. These studies suggest that percepts and ocular responses to tilt are determined by sensing the body vertical relative to the GIA. The findings also raise the possibility that 'artificial gravity' during the Neurolab flight counteracted adaptation of these otolith-ocular responses. Show more

Keywords: vestibulo-ocular reflex, microgravity, otoliths, artificial gravity, countermeasure

DOI: 10.3233/VES-2003-134-620

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 377-393, 2003

Authors: Yates, B.J. | Holmes, M.J. | Jian, B.J.

Article Type: Research Article

Abstract: Immediately following spaceflight, many astronauts are unable to maintain adequate perfusion of the brain after assuming an upright posture; this condition is called post-spaceflight orthostatic intolerance (PSOI). Considerable evidence shows that inputs from otolith organs and other graviceptors play an important role in regulating blood pressure during changes in posture in a 1-g environment. However, reflexes elicited by graviceptors, presumably including those affecting the cardiovascular system, are attenuated during spaceflight. Thus, PSOI could be related to effects of microgravity on the processing of inputs from otolith organs and other graviceptors by the central vestibular system. It is likely that successful …countermeasures for PSOI must address the plastic changes induced in the nervous system by changes in the patterns of graviceptive inputs that occur during spaceflight. Show more

Keywords: cardiovascular, blood pressure, vestibular system, otolith organ, sympathetic nervous system

DOI: 10.3233/VES-2003-134-621

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 395-404, 2003

Authors: Cohen, Helen S.

Article Type: Research Article

Abstract: This paper is an overview of current research on development of rehabilitative countermeasures to ameliorate the effects of long-term exposure to microgravity on sensorimotor function during space flight. After many years of work we do not yet have operational countermeasures, probably for several reasons: 1) changes in the use of vestibular input are manifested in many ways, 2) due to multiple mechanisms for funding research, investigators doing related research may not coordinate their work, and 3) relatively few scientists work on this problem. The number of investigators and physicians who routinely deal with the functional problems of astronauts and the …limitations of working in the space environment is tiny; the number of investigators who are therapists, and who therefore have experience and expertise in developing rehabilitation programs, is miniscule. That's the bad news. The good news is that as a group, we are little but mighty. Therefore, the entire group of investigators can plan to take a more coordinated, collaborative approach than investigators in larger fields. Also, serendipitously, individual research groups have begun approaching different rehabilitative aspects of this problem. If we make a greater effort toward a coordinated, multidimensional approach, guided by rehabilitation concepts, we will be able to provide operational sensorimotor countermeasures when they are needed. Show more

Keywords: vestibular, spaceflight, microgravity, countermeasures, exercise, therapy, rehabilitation, centrifuge, vibrotactile, variable practice, motor learning

DOI: 10.3233/VES-2003-134-622

Citation: Journal of Vestibular Research, vol. 13, no. 4-6, pp. 405-409, 2003