Visually-induced sickness in normal and bilaterally labyrinthine-defective subjects.

A group of nine normal subjects (with no overt vestibular dysfunction) and a group of 6 bilaterally labyrinthine-defective subjects were exposed to a visual field rotating about an Earth-horizontal axis (orthogonal to the gravity axis). The visual stimulus was provided by a 3-m diameter sphere with random dots rotating at 30, 45, and 60 degrees per second (degree/s) about the stationary subject's roll, pitch and yaw axes. The subject's head was positioned at the center of the sphere such that it experienced apparent motion in all three axes. Results indicated that in the normal group, symptoms of motion sickness were reported in 21 of 27 test-trials. When labyrinthine-defective subjects were exposed to the roll and pitch stimulus, no sickness symptoms were reported or observed. These results strongly suggest that the vestibular system is necessary for sickness induced by moving visual fields.     

Head movement induced by angular oscillation of the body in the pitch and roll axes.

The transmission of angular acceleration to the head of the human subject has been investigated during sinusoidal angular oscillation of the body in either pitch or roll about an axis through the upper lumbar vertebrae. The results indicated that angular acceleration of the skull was induced in all three axes of the head by both pitch and by roll motion. At frequencies below 1-2 Hz the head moved with the body, but in the frequency range 2-8 Hz the amplitude of head acceleration was augmented indicating that oscillation about a centre of rotation low in the body may induce large angular movements in this frequency range because of the linear component of acceleration delivered at the cervical vertebrae. At higher frequencies, the acceleration at the head was attenuated with an associated increase in phase lag, probably due to the absorption of input acceleration by the upper torso.     

Eye movements to yaw, pitch, and roll about vertical and horizontal axes: adaptation and motion sickness

BACKGROUND: In the search for parameters to predict motion sickness that can be measured in the laboratory, we performed a longitudinal investigation in aviators. Since the vestibular system is involved in the generation of motion sickness as well as eye movements, vestibulo-ocular reflex (VOR) parameters seemed relevant. We investigated three topics: 1) the effect of axis orientation and its orientation to gravity on the VOR; 2) changes in VOR parameters depending on flight experience; and 3) differences in VOR parameters in aircrew with high and low susceptibility to motion sickness. HYPOTHESIS: Nystagmus decay after angular velocity steps would be faster for non-susceptible and trained aviators. METHODS: We recorded eye movements evoked by angular on-axis velocity steps (+/- 90 degrees x S(-2), to and from 90 degrees x S(-1)) in yaw, pitch, and roll, about both the Earth vertical and Earth horizontal axes in 14 subjects with a low susceptibility to motion sickness. These data were compared with those of 10 subjects with a high susceptibility. RESULTS: Horizontal axis rotations are nauseogenic. We found that during (per) and post-condition, left- and rightward rotation responses were equal, and the orientation with respect to gravity did not alter the basic nystagmus decay, apart from a sinusoidal modulation. Moreover, pitch and roll rotations show equal nystagmus decays, significantly faster than for yaw; yaw and pitch peak velocities were equal and were larger than for roll. With regard to changes in VOR parameters depending on flight experience, we found that repeated vestibular stimulation reduced nystagmus decay as well as the otolith modulation. With respect to the changes in VOR parameters and motion sickness susceptibility, we found that subjects highly susceptible to motion sickness showed a slower decay of nystagmus with a larger peak velocity than less susceptible subjects. CONCLUSIONS: Group averages indicate a difference in eye movement parameters, only in yaw, depending on flight experience; and between subjects with low and high susceptibility to motion sickness. The involvement of the velocity storage mechanism as realized by an internal model is given as a plausible explanation.     

The effects of roll vs. pitch rotation in humans under orthostatic stress.

BACKGROUND: It has been known since 1953 that pre-exposure to less than +1 Gz will reduce subsequent +Gz-tolerance. With few exceptions, during operational flying, the transition from hypogravity to hypergravity involves roll as well as pitch rotation. We examined the effect of roll vs. pitch rotation while undergoing transition from hypogravity to +1 Gz on a tilt table. METHODS: Twelve subjects (28-47 yr old) were rotated at 45 degrees x s(-1) from head-up (HU) at 15 degrees relative to gravitational vertical to 135 degrees head-down (HD) and back to the HU position after different HD dwell times. HD dwell times were set at 7, 15, and 30 s. The subject was rotated about the interaural axis (pitch) and about the naso-occipital axis (roll). Both the HD dwell times and axes of rotation were randomized within and across subjects. BP and heart rate were recorded during the HU-HD-HU maneuver. RESULTS: Analysis of variance, repeated measure design revealed that the rate and magnitude of BP decrease induced by the HD to HU maneuver is significantly higher (p < 0.01) in roll than in pitch during all HD dwell times. The decrease of BP at 7s is significantly (p < 0.01) higher than at 15s and 30s. Heart rate increases significantly higher (p < 0.01) in pitch than in roll at 7s-dwell time. CONCLUSION: Our results suggest that the compensatory mechanism to orthostatic stress is more efficient in response to pitch than roll rotation. This is reflected from the findings that the mean magnitude of OH (orthostatic hypotension) and the rate of BP decrease induced by the HD-HU maneuver is significantly greater in roll rotation than pitch rotation. The mean HR increase post HD-HU rotation is significantly higher in the pitch than the roll rotation. The significant rate of BP decrease during HD-HU roll rotation could have important implications for maintaining G-tolerance and spatial orientation during subsequent exposure to hypergravity.     

Effect of roll oscillation frequency on motion sickness

BACKGROUND: In many environments associated with motion sickness there are low frequency motions in several axes, including roll. Roll motion has often been assumed to be a cause of motion sickness, either alone or in combination with motions in other axes. However, there have been no systematic studies of the effects of roll frequency on sickness. HYPOTHESIS: It was hypothesized that sickness caused by roll oscillation would depend on the frequency of roll. METHOD: There were 100 male subjects (aged 18 to 26 yr) who participated in a laboratory study. Prior to experiencing motion, all subjects completed a motion sickness history questionnaire giving information on travel and motion sickness experience. The seated subjects were exposed within a closed cabin to 30 min of sinusoidal roll motion at one of five frequencies: 0.025 Hz, 0.05 Hz, 0.10 Hz, 0.20 Hz, or 0.40 Hz. At each frequency, the cabin oscillated through +/-8 degrees about a center of rotation located on the seat surface. Ratings of motion sickness were obtained at 1-min intervals. RESULTS: Subject illness ratings were positively correlated with their previous motion sickness, although at each frequency the amount of sickness was small. Overall, there was no significant difference in the sickness ratings produced by the five motions. CONCLUSIONS: The frequency dependence of motion sickness produced by roll oscillation differs from that associated with vertical and horizontal oscillation. Motion sickness associated with pure roll oscillation of a seat will usually be less than the sickness associated with pure translational oscillation of the seat or the sickness associated with combined translation and rotation.     

Visual-vestibular interaction in the control of eye movement.

Three experimental conditions have been used to investigate the extent to which inappropriate reflex eye movements of vestibular origin can be suppressed by visual feedback. First, the ability to read digits in a display which moved with the head was assessed during angular oscillation about the yaw and pitch axes of the body. Performance decrement was observed at frequencies above 0.2 Hz in pitch and 1.0 Hz in yaw, being greater at higher stimulus velocity levels. A second experiment revealed that the performance decrement was associated with eye movements relative to the head, which increased with the frequency of stimulation. Finally, the response of the pursuit reflex was investigated under similar experimental conditions. The results indicated that the breakdown in the pursuit reflex and in the suppression of the vestibulo-ocular reflex occurred over the same frequency band, implying the similarity of the mechanisms responsible for suppression and pursuit.     

The effects of visual scenes on roll and pitch thresholds in pilots versus nonpilots

BACKGROUND: Previous studies have indicated that, compared with nonpilots, pilots rely more on vision than "seat-of-the-pants" sensations when presented with visual-vestibular conflict. The objective of this study was to evaluate whether pilots and nonpilots differ in their thresholds for tilt perception while viewing visual scenes depicting simulated flight. METHODS: This study was conducted in the Advanced Spatial Disorientation Demonstrator (ASDD) at Brooks AFB, TX. There were 14 subjects (7 pilots and 7 nonpilots) who recorded tilt detection thresholds in pitch and roll while exposed to sub-threshold movement in each axis. During each test run, subjects were presented with computer-generated visual scenes depicting accelerating forward flight by day or night, and a blank (control) condition. RESULTS: The only significant effect detected by an analysis of variance (ANOVA) was that all subjects were more sensitive to tilt in roll than in pitch [F (2,24) = 18.96, p < 0.001]. Overall, pilots had marginally higher tilt detection thresholds compared with nonpilots (p = 0.055), but the type of visual scene had no significant effect on thresholds. CONCLUSION: In this study, pilots did not demonstrate greater visual dominance over vestibular and proprioceptive cues than nonpilots, but appeared to have higher pitch and roll thresholds overall. The finding of significantly lower detection thresholds in the roll axis vs. the pitch axis was an incidental finding for both subject groups.     

Visual sensations of roll rotation during complex vestibular stimulation

BACKGROUND: In aviation, vestibular-induced spatial disorientation is a significant cause of accidents. Recreating flight-like vestibular stimuli in simulators might be a means for training pilots to respond adequately in disorienting situations. Due to the physical constraints of land-based simulators, the question arises whether a given illusion may be created in different ways. For instance, is it possible to induce sensations of tilt by rotary stimuli? The present study concerns the relationship between sensations of rotation and tilt during complex vestibular stimulation. METHODS: The visual sensation of roll rotation was quantified by means of a velocity-matching procedure. In a large gondola centrifuge eight subjects underwent four runs (2 G, 2 min) with different heading positions (forward, backward, centripetally, and centrifugally). The inclination of the gondola persistently corresponded with the vector sum of the Earth gravity force and the centrifugal force (60 degrees at 2 G). Thus, the semicircular canal stimulus in roll was combined in different ways with stimuli in yaw and pitch, as well as with an increasing or decreasing G vector. RESULTS: The magnitude of the responses was only dependent on the roll component of the stimulus. The gain, defined as the ratio between the response and the roll stimulus, was 7-10%. The responses decayed with a time constant ranging from 4 to 5.5 s. CONCLUSION: The visual sensation of roll rotation reflects the roll plane canal velocity stimulus independently of other stimulus components. This is in contrast to earlier findings on the sensation of changes in position (roll tilt).     

Vestibular nystagmus as a result of the interactions between semicircular canals and the otolithic membrane subsystems of the vestibular system]

Untreated and treated (unilateral section of utricular and saccular branches of the vestibular nerve) pigeons Columba livia were rotated in the dark in the horizontal plane, the head being in a different position relative to the axis of rotation. The range of angular acceleration was 7-19 deg/c2 and the peak value of centrifugal acceleration was 0.5 g. The neck and eye nystagmus was recorded. It was found that: 1) the result of canal-otolith interaction was not directly related to the pattern of changes of otolith afferentation but was determined by the ratio of otolith afferent signals in the right and left labyrinths and, consequently, by the ratio of patterns of activities in the CNS paired structures that receive otolith afferentation; 2) the same result of interaction (enhancement or attenuation of vestibular responses) can be achieved through both increase or decrease of otolith afferentation; 3) if joint stimulation of semicircular canals and otolith organs induces asymmetry of neuronal activities of paired brain structures that perceive otolith afferentation, then, irrespective of the mechanism of origin of this asymmetry, it is followed by changes of oppositely directed nystagmus of different sign (increase for one nystagmus and decrease for the other). It is concluded that the symmetry of reactions recorded in response to isolated stimulation of semicircular canals (otolith organs) cannot be considered as a reliable criterion of functional symmetry of semicircular canals (otolith organs).     

Effects of caloric vestibular stimulation on head and trunk movements during walking

The effects of vestibular stimulation on head and trunk movements were investigated during human walking (4.0 km/h). Vestibular stimulation was produced by irrigating an external auditory meatus with 4 °C ice water for 10 s. Using a 3-D motion analysis system, the linear (medial/lateral and vertical) translations and angular (yaw, pitch and roll) rotations were determined at the head, thorax, pelvis, knee, and foot. After caloric stimulation, waking trajectory deviated toward the stimulated side during dizziness. In addition, the amplitude of medial/lateral (M/L) linear translation and yaw rotation were significantly increased by caloric stimulation, especially at the head and thorax, whereas changes in vertical translation and pitch and roll rotations were not significant. The compensatory coordination (i.e., the yaw rotation to oppose the M/L linear translation) of the head was precisely maintained both before and after caloric stimulations, but it was decreased at the thorax and pelvis after stimulation. Our results suggested that vestibular sensory information, probably via the horizontal semicircular canals, contributes predominantly to the regulation of dynamic head and trunk movements in the M/L direction.     

Thresholds of perception for periodic linear motion.

This paper reviews 18 reports which have investigated the absolute threshold of perception of periodic linear motion. The roles of the otolith, somatosensory, and visual detection mechanisms in determining threshold are discussed. Most threshold data for oscillation at frequencies below 1 Hz reflect otolith and somatosensory detection, and show a falling threshold as the frequency rises. This is in accord with neurophysiological data of otolith and somatosensory function. The data for frequencies above 1 Hz reflect an unknown mix of visual, otolith, and somatosensory influences. These data are too heterogenous to indicate whether threshold rises or falls as the frequency of stimulation increases.     

Subjective effects of combined-axis vibration: II. Comparison of X-axis and X-plus-pitch vibrations

Seated subjects matched their perceptions of the intensity of single-axis vibrations in the X axis, or combined-axis vibrations made up of X-axis and pitch motions, by adjusting the intensity of a sinusoidal, 5 Hz, Z-axis response vibration. Stimulus vibrations were sinusoidal at 3.15, 4, 5, 6.3 and 8 Hz. For each frequency, both types of vibration were presented at three acceleration levels related to three axis-to-seat distances for the pitch vibrations. Results showed that Z-axis response accelerations were essentially constant across frequency. However, matching responses were significantly higher for X-plus-pitch than for X-axis vibrations. These findings are in contrast to those of a previous experiment involving Y-axis and roll vibrations, and are probably due to additional input from the seat back for X and pitch motions. The two experiments do agree on the importance of the distance of the subject from the axis of rotation for angular motions. In both experiments, as stimulus acceleration (axis-to-seat distance) increased, response acceleration increased substantially at every frequency.     

Directional effects of biofeedback on trunk sway during gait tasks in healthy young subjects

Biofeedback of trunk sway is a possible remedy for patients with balance disorders. Because these patients have a tendency to fall more in one direction, we investigated whether biofeedback has a directional effect on trunk sway during gait.Forty healthy young participants (mean age 23.1 years) performed 10 gait tasks with and without biofeedback. Combined vibrotactile, auditory and visual feedback on trunk sway in either the lateral or anterior–posterior (AP) direction was provided by a head-mounted actuator system. Trunk roll and pitch angles, calculated from trunk angular velocities measured with gyroscopes, were used to drive the feedback.A reduction in sway velocities occurred across all tasks regardless of feedback direction. Reductions in sway angles depended on the task. Generally, reductions were greater in pitch. For walking up and down stairs, or over barriers, pitch angle reductions were greater with AP than lateral feedback. For tandem and normal walking, reductions were similar in pitch and roll angles for both feedback directions. For walking while rotating or pitching the head or with eyes closed, only pitch angle was reduced for both feedback directions.These results indicate that the central nervous system is able to incorporate biofeedback of trunk sway from either the AP or lateral direction to achieve a reduction in both pitch and roll sway. Greater reductions in pitch suggest a greater ability to use this direction of trunk sway biofeedback during gait.     

Motion sickness: effect of the magnitude of roll and pitch oscillation

BACKGROUND: Rotational oscillation in roll and pitch can cause motion sickness, but it is not known how sickness depends on the magnitude of rotational oscillation or whether there is a difference between the two axes of motion. HYPOTHESIS: It was hypothesized that motion sickness would increase similarly with increasing magnitudes of roll and pitch oscillation. METHOD: There were 120 subjects (6 groups of 20 subjects) who were exposed to 30 min of 0.2-Hz sinusoidal roll or pitch oscillation at 1 of 3 magnitudes: 1) +/- 1.830; 2) +/- 3.66 degrees; or 3) +/- 7.32 degrees. Subjects sitting in a closed cabin with their eyes open gave ratings of their illness on a 7-point illness rating scale at 1-min intervals. RESULTS: Over the six conditions, mild nausea was reported by 17.5% of subjects. With both roll oscillation and pitch oscillation, mean illness ratings were least with +/- 1.83 degrees of rotational oscillation and greater with +/- 3.66 degrees and +/- 7.32 degrees of oscillation. At none of the three magnitudes of oscillation was there a significant difference in motion sickness caused by roll and pitch oscillation. CONCLUSIONS: With rotational oscillation about an Earth-horizontal axis, there is a trend for motion sickness to increase with increasing motion magnitude. For the conditions investigated, similar motion sickness was caused by roll and pitch oscillation.     

Differences between trunk sway characteristics on a foam support surface and on the Equitest ankle-sway-referenced support surface

Clinicians have sought ways to increase trunk sway so that it is easily observed and a balance deficit more easily identified. One technique often used for this purpose is to reduce the efficacy of ankle proprioceptive inputs on sway. To achieve this reduction either a foam mat is used as an unstable support surface or the subject stands on a surface made unstable with servo-driven ankle-sway-referencing. The purpose of the current study was to investigate differences in trunk pitch and roll sway characteristics using these techniques. Trunk sway while standing quietly on two legs was measured in 25 normal subjects in the age range 20–35 years for three support-surface conditions. Each condition was tested twice for 20 s, once with eyes open and once with eyes closed. The three conditions were standing on a foam support surface, standing on a support surface with pitch (fore-aft) ankle-sway-referencing as used for the standard Sensory Organization Test (SOT) of the Neurocom Equitest System (SOT 4 and 5), and standing with roll (lateral) ankle-sway-referencing. The latter was achieved by having the subjects stand turned 90° to the standard SOT position. Two angular velocity sensors mounted on a belt measured trunk sway in the pitch and roll directions. Trunk roll angle and angular velocity amplitudes for pitch sway-referencing were reduced compared to either the foam or roll sway-referencing conditions, but trunk pitch angle and angular velocities amplitudes were greater. For roll sway-referencing, the trunk roll angle was greater than for the other stimulus conditions. Analyses of the trunk sway velocity in the frequency domain indicated that ankle-sway-referencing in the pitch direction increased trunk pitch sway at 1 Hz and decreased trunk roll sway between 2 and 5 Hz compared to foam support frequency spectra. Roll ankle-sway-referencing decreased trunk roll between 2 and 4 Hz only. These results indicate that using a foam support surface provides multidirectional trunk sway with velocity content across all frequencies in the range 0.8–5.2 Hz. Roll ankle-sway-referencing, but not pitch ankle-sway-referencing, yields trunk sway with similar characteristics to those with foam. Pitch ankle-sway-referencing forces pitch trunk resonance to be around 1 Hz and yields very different trunk sway from that obtained with a foam support surface. Roll sway-referencing is an alternative means to test multidirectional control of sway. Clinically though, foam is simpler to use and provides a more difficult balance task for the patient.     

Human tilt perception in a dynamic environment.

This study examines the perception of tilt and linear acceleration as sensed through the utricular otolith of the vestibular system. Any sensation derived from the otolith is a consequence of the displacement of the otolith parallel to its own plane. This leads, naturally, to the definition of a sensation plane. A model is presented which defines this sensation plane. It assumes that the sacular otolith contribution is negligible, an assumption substantiated by correlation with experimental data by Sch?ne. Applying this model to perceived pitch angle, a simple equation is presented which relates the number of Gs and actual pitch angle to the perceived pitch angle. Experimental data are needed to develop perceived sensation curves for the sensation plane. The model implies that a state of confusion exists outside the realm of our prior experiences. Disorientation or motion sickness may be related to this confused state. In addition, new avenues of inquiry are introduced.     

猫耳石器官破坏后线性加速度作用下半规管反应特点

本研究用手术方法破坏猫耳石器官,在平行秋千和径向加速度作用下,观察到猫手术前和双侧耳石损伤后,耳石—眼动反射动力学特性(功率谱和相对增益)有非常显著性差异;在线性加速度下脊髓反射H 波幅的反应模式被破坏;皮层体感诱发电早成分(N1,P1)潜时和幅度发生显著性改变;旋转刺激下眼震衰减率无显著性差异;而单侧耳石损伤后与手术前相比,眼震衰减率有显著性降低,说明耳石单侧损伤后不仅耳石功能不对称,也引起半规管不对称,反映了耳石半规管之间调制作用。我们认为,潜在性耳石和半规管功能不对称可能是产生空间前庭功能障碍的主要原因。     

持续高+Gy对豚鼠耳石器的影响

目的观察持续高Ｇ刺激对耳石器的影响。方法应用原位杂交技术观察了１６只豚鼠在＋３Ｇｙ、＋１０Ｇｙ和＋１８Ｇｙ持续刺激１５ｍｉｎ后,前庭囊斑感觉上皮细胞中ｃ－ｆｏｓｍＲＮＡ和ＢＭＰ１ｍＲＮＡ表达量的变化,并观察了高Ｇ刺激后动物的行为变化。结果三种刺激量均引起豚鼠姿势不稳,出现前庭功能不平衡的症状,并引起中耳腔出血;前庭囊斑感觉上皮中ｃ－ｆｏｓ及ＢＭＰ１ｍＲＮＡ的表达量明显增加。结论＋３Ｇｙ以上的高Ｇ刺激可引起豚鼠出现前庭功能不平衡症状,改变前庭囊斑感觉上皮中细胞因子的表达     

Structural resistance of receptor organs of the vestibular apparatus to the factors of space flight

Observations made in ground-based simulation studies and in real orbital flights on fish and amphibian larvae as well as on adult rats show that exposure to different space flight factors, particularly microgravity, for as long as 20 days produces no pathological changes in the structural organization of vestibular receptors. However the possibility of functional or adaptive rearrangements in maculae and crystae as well as in the otolith organ cannot be excluded. It appears that bony fish (Teleostei) are most suitable for the study of adaptive changes in the otolith apparatus. When examining ultrastructural changes in maculae and crystae, it is important to take into consideration spatial and structural nonhomogeneity of the receptor epithelium of vestibular organs.     

超重错觉的地面模拟

目的观察在超重环境下由于动头或座舱姿态变化所引起的定向知觉,探讨在地面用高级空间定向障碍模拟器模拟超重错觉的可行性.方法用模拟器匀速旋转产生1.6G的超重环境,12名男性战斗机飞行员分别于俯仰平面内抬头前后和滚转平面内座舱倾斜姿态改变前后报告其定向知觉.结果在俯仰平面,被试者完成抬头动作后,体会到座舱发生了63.8°±48.3°的上仰;在滚转平面,当座舱向左倾斜20°后,被试者体会到座舱向左发生了48.6°±39.4°的倾斜.结论虽然在模拟器上有较强的Cori-olis效应存在,大多数被试者均体验到了超重错觉,在地面用模拟器模拟超重错觉是可行的.