Disruption of postural readaptation by inertial stimuli following space flight.

Postural instability (relative to pre-flight) has been observed in all shuttle astronauts studied upon return from orbital missions. Postural stability was more closely examined in four shuttle astronaut subjects before and after an 8 day orbital mission. Results of the pre- and post-flight postural stability studies were compared with a larger (n = 34) study of astronauts returning from shuttle missions of similar duration.

Motion sickness and development of synergy within the spatial orientation system. A hypothetical unifying concept.

Adaptation to research paradigms such as rotating rooms and optical alteration of visual feedback during movement results in development of perceptual-motor programs that provide the reflexive assistance that is necessary to skilled control of movement and balance. The discomfort and stomach awareness that occur during the adaptation process has been attributed to conflicting sensory information about the state of motion. Vestibular signals depend on the kinematics of head movements irrespective of the presence or absence of signals from other senses.

Microgravity vestibular investigations: perception of self-orientation and self-motion.

Four astronauts experienced passive whole-body rotation in a number of test sessions during a 7-day orbital mission. Pitch (Y-axis) and roll (X-axis) rotation required subject orientations on the rotator in which the otolith system was at radius of 0.5 m.

Vertical optokinetic nystagmus and after-responses during backward tilt.

Method: Vertical optokinetic nystagmus (VOKN) and after-responses were detected in nine subjects using the corneo-retinal potential (CRP) technique and an infrared video camera detection apparatus (ISCAN) simultaneously. The ISCAN method produced a much smaller inter-subject variability, a higher linear regression coefficient (0.94) when vertical eye position was regressed against vertical target position (+/- 30 degrees, 5 degrees increments).

Spatial orientation perception and reflexive eye movements--a perspective, an overview, and some clinical implications.

When head motion includes a linear velocity component, eye velocity required to track an earth-fixed target depends upon: a) angular and linear head velocity, b) target distance, and c) direction of gaze relative to the motion trajectory. Recent research indicates that eye movements (LVOR), presumably otolith-mediated, partially compensate for linear velocity in small head excursions on small devices. Canal-mediated eye velocity (AVOR), otolith-mediated eye velocity (LVOR), and Ocular Torsion (OT) can be measured, one by one, on small devices.

Vestibulo-ocular response of human subjects seated in a pivoting support system during 3 Gz centrifuge stimulation.

The vestibulo-ocular reflex (VOR) and spatial orientation perceptions were recorded in 15 subjects during 3 Gz centrifuge runs. These data were obtained to study two issues: (1) to gain insight into reports of asymmetrical disorientation and disturbance during acceleration and deceleration of centrifuge runs like those used to train pilots on the procedures to counteract G-induced loss of consciousness (G-LOC); (2) to study the effects of sustained vertical linear acceleration on the vestibular system. The centrifuge angular velocity profile consisted of a 19 s angular acceleration to 3 Gz that was sustained for 5 min during a period of constant angular velocity, and a 19 s deceleration to 1 Gz.

Space vestibulo-neuroscience in the new century: why proceed in semi-darkness?

With advancing technology, neuroscientists have explored vestibular transducer microstructure and molecular processes, neural pathways of interaction between vestibular visual and proprioceptor systems and neurochemical processes of adaptive change. Progress in space vestibulo-neuroscience will be fostered by focus on interactions among the systems involved in whole-body movement relative to the earth. Description of perceptual and sensorimotor reactions to complex accelerative stimuli during goal-directed and passive movement is crucial to conceptualizing the functional significance of various interactions and viable theory.

Perception of motion and position relative to the earth. An overview.

Results of the five experiments are consistent with the following generalizations. Canal-mediated turn perception (pitch, roll, or yaw) in earth-horizontal or earth-vertical plane, is suppressed in direct relationship to the magnitude of a linear acceleration vector lying in the plane of a responding canal when the magnitude of the linear vector is constant or increasing and when its direction is either fixed or rotating in the same direction as the concomitant canal signal. Canal-mediated turn perception (pitch, roll, or yaw) is not suppressed by a coplanar linear vector that is counterrotating relative to the canal signal.

The dynamics of spatial orientation during complex and changing linear and angular acceleration.

The dynamics of spatial orientation perception were examined in a series of experiments in which a total of 43 subjects were passively exposed to various combinations of linear and angular acceleration during centrifuge runs. Perceptual effects during deceleration were much stronger than effects during acceleration. The dynamics of spatial orientation perception differed substantially from changes in the vestibulo-ocular reflex (VOR).

Steady state and transient G-excess effects.

Acceleration forces of flight are associated with a number of spatial orientation illusory effects. This note focuses on two effects, both called the "G-excess effect." A distinction between steady-state and transient G-excess effects is important because prescriptions for preventive management of effects in flight will differ.

The influence of active versus passive head oscillation, and mental set on the human vestibulo-ocular reflex.

We compared passive (manual) whole body, and active head oscillation in normal human subjects attempting mentally to influence the vestibulo-ocular reflex (VOR). Our objective was to establish simple procedural guidelines for vestibular test procedures in clinical settings. Using a head-fixed target, both methods of oscillation yielded virtually zero gain.

Performance-based assessment of oculomotor efficiency.

Acquisition of visual information from spatial points disparate enough to necessitate head and eye movement involves the vestibular and other oculomotor control systems in shifting and stabilizing gaze relative to those points. In the present study, a simple procedure to test oculomotor abilities was developed and evaluated; it uses performance (serial letter identification) to maintain initial gaze position and performance (number of digits correctly identified) to measure the efficiency of gaze-shift control. Number of digits acquired from briefly displayed digit sets was consistently and powerfully influenced by exposure duration of digit sets and to a lesser extent by the size of required gaze shift.

Aerobic fitness and susceptibility to motion sickness.

Susceptibility to motion sickness was evaluated in 29 males having high, moderate, and low levels of aerobic fitness. Subjects underwent Coriolis (cross-coupled) vestibular stimulation on a Stille-Werner rotator during a 10 min modification of the Brief Vestibular Disorientation Test (BVDT). Variables evaluated were: spin time before aborting (ST), heart rate (HR), respiratory rate (RR), mean skin temperature (Tsk), subject observation values (SV), and observation values (OV).

Modification of per- and postrotational responses by voluntary motor activity of the limbs.

In order to explore interactive effects of voluntarily generated rotational stimuli on evoked vestibular responses, experiments were performed using a rotation chair in which the subject either controlled the angular motion by voluntary movement of his upper and lower limbs, or was passive-rotation being controlled by a servomotor and electromagnetic brake. In two experiments, carried out on 8 and 9 subjects respectively, it was found that cessation of sustained passive rotation by voluntary limb actions strongly suppressed the postrotational turning sensation but did not alter the evoked nystagmus. Limb movements that were directionally concordant with muscle torque in generating body rotation yielded arthrokinetic effects which augmented perrotational nystagmus and sustained the sensation of turning.

Influence of a visual display and frequency of whole-body angular oscillation on incidence of motion sickness.

Visual search within a head-fixed display consisting of a 12 X 12 digit matrix is degraded by whole-body angular oscillation at 0.02 Hz (+/- 155 degrees/s peak velocity), and signs and symptoms of motion sickness are prominent in a number of individuals within a 5-min exposure. Exposure to 2.

Apparent instrument horizon deflection during and immediately following rolling maneuvers.

There have been recent reports by pilots of apparent visual bending or bowing of instrument horizons during and immediately following ascending rolling maneuvers in the F-14 aircraft. The present study investigates the probability that normal reflex actions may partially account for the illusions cited in these reports. The results of this study suggest that the vestibulo-ocular reflex (VOR) can produce an apparent deflection of the instrument horizon (actually an apparent flicking back and forth) during and after roll maneuvers involving high peak angular velocities.

The vestibulo-ocular reflex in man during voluntary head oscillation under three visual conditions.

The vestibulo-ocular reflex (VOR) generated by voluntary head movements keyed to a tone varying sinusoidally in pitch was studied in 13 men. Modulation of pitch at frequencies ranging from 0.1-5.

Visual-vestibular interactions: the directional component of visual background movement.

Legibility of a head-fixed display and visual suppression of the vestibulo-ocular reflex (VOR) were found to be superior when vestibular stimuli and optokinetic stimuli were of like direction (i.e. would produce the same directions of nystagmus) and inferior when they were opposite in direction.

Visual-vestibular interactions: I. Influence of peripheral vision on suppression of the vestibulo-ocular reflex and visual acuity.

Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function.

Motion sickness susceptibility: a retrospective comparison of laboratory tests.

A test battery designed primarily to assess vestibular function has been used for several years to evaluate individuals referred to our laboratory. Because some of the test conditions have proved to be nauseogenic to some individuals, methods of assessing disturbance during these procedures have been used to pursue a second goal, viz., the estimation of motion sickness susceptibility.

Visual counteraction on nauseogenic and disorienting effects of some whole-body motions: a proposed mechanism.

It has been indicated that the nauseogenic and disorienting effects of several kinds of provocative motion stimuli can be ameliorated by visual reference to the Earth. The purpose of the present experiment is to investigate a hypothesis concerning the mechanism of this beneficial effect. The results demonstrate that the aftereffects of large-field optokinetic stimulation can nullify the nauseogenic and disorienting effects of Coriolis cross-coupled vestibular stimuli.

Coriolis cross-coupling effects: disorienting and nauseogenic or not?

Nausea and disorientation are sometimes produced by head movements during turning maneuvers in aircraft. These responses are usually attributed to Coriolis cross-coupling stimulation of the vestibular system, although it has been indicated recently that many turning maneuvers of aircraft have insufficient angular velocity to generate such effects. The purpose of the present study was to further distinguish conditions in which Coriolis cross-coupling effects are disorienting and nauseogenic from conditions in which they are neither.

Antisomatogyral illusion.

Following voluntary ambulatory turning (eight turns), perceived motion is reversed in direction relative to a) aftereffects of passive rotation and b) predictions from current concepts of immer ear function. Following active turning, feedback from reflexes elicited by vestibulospinal activity apparently dominates the perceptual experience. Practical consequences in medicine and aviation are discussed.