Visual display lowers detection threshold of angular, but not linear, whole-body motion stimuli

The influence of a visual display, fixed relative to the subject, on thresholds for detection (at 75% correct) of discrete Y-axis linear movements and of discrete Z-axis angular movements, was determined in a group of 12 subjects. Both the linear and the angular, whole-body, motion stimuli had a cosine bell velocity trajectory with a duration of 2.6 s. Thresholds for the detection of the linear motion stimuli in darkness were not significantly different from those obtained when either a simple LED display or an instrument dial were illuminated; the mean threshold was 0.039 m.s-2. None of the subjects reported apparent movement of the visual display. In contrast, the presence of either visual display lowered angular motion thresholds on average by a factor of 2.7 from that obtained in darkness (1.61 degrees.s-1). All subjects reported apparent movement of the visual display, an oculogyral illusion, at stimulus intensities close to the dark threshold. These findings imply that otolithic afferents, unlike those from the semicircular canals, do not interact with neural centres mediating visual localization.     

短臂离心机不同转速暴露时躯体重力错觉及前庭自主神经反应对比

目的观察短臂离心机不同转速暴露时躯体重力错觉诱发效果及前庭自主神经反应情况,寻求短臂离心机用于地面模拟训练的适合转速。方法在SAC-Ⅲ型短臂离心机不同转速下,对105名健康歼击机飞行员进行躯体重力错觉模拟,对比错觉诱发情况及前庭自主神经反应情况。结果短臂离心机启动加速、匀速运行及制动减速阶段可分别诱发出前倾扭转错觉、前倾错觉及后倾错觉等躯体重力错觉,3种转速下各躯体重力错觉形态表现相同,但错觉强度随离心机转速加快而增强。37 r/min暴露时,各错觉诱发率均大于30 r/min和21 r/min暴露时的诱发率(P0.01);30 r/min和21 r/min暴露时,各错觉诱发率差异均无统计学意义P0.05)。3种转速下前庭自主神经反应评分分值随转速增加有增高趋势,但差异无统计学意义(P0.05)。结论 37 r/min短臂离心机暴露时躯体重力错觉的诱发率高,且前庭自主神经反应较轻,此转速用于飞行人员躯体重力错觉的地面模拟训练较为适合。     

Rotation rate and duration effects on the somatogyral illusion

INTRODUCTION: Aviation spatial disorientation mishaps remain a concern, especially due to their fatality rate. Some of the most insidious disorientations are due to vestibular stimuli in the absence of visual cues. A category of such disorientations are known as somatogyral illusions. METHODS: To determine the effects of spin rate and duration on the perception of the somatogyral illusion, we examined the subjective response of pilots and non-pilots to rotation around the yaw axis in a flight simulator in a manner that would mimic two vestibular illusions found in flight: the washout of the semi-circular canals following sustained turns, and the illusory counter-rotation following return to straight and level flight. There were 29 subjects (14 pilots) who were seated blindfolded in a flight simulator which accelerated to constant plateau rotation rates of 20, 70, and 120 degrees x s(-1) and then decelerated to stationary; plateaus were 10, 20, or 40 s. Subjects reported 1) the time when the perception of rotation ceased (i.e., the subjective time until washout was reached); 2) the relative magnitude of the counter-rotation experienced; and 3) the time until the perception of counter-rotation ceased. Subjects also manipulated a slider to provide a continuous subjective measure of their experience of rotation. RESULTS: The two time measures increased with increases in both the duration and magnitude of the spin. The increase in perceived washout time with spin rate was non-linear (geometric). There was an interaction between spin duration and spin rate on the experience of illusory counter-rotation magnitude such that at low rates, spin duration had no effect, but its effect increased at faster rates. The time constant of adaptation of the semicircular canals was estimated to be 8.3 s. DISCUSSION: The effects were validated against a model of semicircular canal and cupola adaptation, which predicted the data with high accuracy. Pilots and non-pilots did not differ in their illusory experience.     

飞行员地面错觉模拟及其反应参考值

目的 验证地面错觉训练方案在我军飞行员航空医学训练中应用的可行性,为评价地面错觉模拟训练效果提供参考值.方法 在我军现有错觉模拟训练方案基础上,参照北大西洋公约组织推荐的地面错觉模拟训练方案,依据现有的设备,对80名健康飞行员进行地面错觉模拟训练.在VTS-0型电动转椅上进行躯体旋动错觉、科里奥利错觉模拟,在VTS-Ⅲ型前庭功能检查系统上进行相对运动性错觉、自动性错觉模拟,观察错觉的诱发情况,并进行相应错觉反应参数（错觉持续时间、潜伏期）的记录.结果 躯体旋动错觉、科里奥利错觉、相对运动性错觉和自动性错觉的诱发率分别为100.0%、90.7%、72.5%和49.2%.前庭性错觉的诱发率要大于视性错觉（χ2=5.01,P〈0.05）.飞行员躯体旋动错觉、科里奥利翻转错觉、科里奥利滚转错觉的持续时间分别为（8.4±4.5）s、（4.9±2.3） s、（5.4±3.0） s;相对运动性错觉、自动性错觉的潜伏期分别为（34.8±19.0） s、（42.8±15.2） s.5种错觉反应数据的参考值分别为：躯体旋动错觉持续时间≤17.4 s,科里奥利滚转错觉持续时间≤11.4 s,科里奥利翻转错觉持续时间为0.3～9.5 s,相对运动性错觉潜伏期≤72.8 s,自动性错觉潜伏期为12.4～73.2 s.结论 立足现有训练装备,我军飞行员躯体旋动错觉、科里奥利错觉、相对运动性错觉及自动性错觉的地面模拟训练方案是有效的、可行的.5种错觉反应数据的参考值可望为飞行员地面错觉模拟效果评价提供依据.     

视错动觉的事件相关电位研究

目的 利用事件相关电位(ERPs)研究视错动觉形成的神经基础.方法 10名健康大学生,均为右利手.刺激图形是由Akiyoshi Kitaoka制作的视错动觉"麦浪图"以及由"麦浪图"修改成的静止图,随机均匀出现100次,呈现时间为2000 ms.让被试者对图形做"动"和"不动"的判断,同时记录其128导脑电.结果 1)错觉图和非错觉图都能够诱发1个ERP早成分C1,其幅度在刺激呈现后75 ms左右达到峰值,错觉图诱发负性C1成分,而非错觉图的C1成分极性相反.2)错觉图和非错觉图都能够诱发明显的P100和P200成分,而且非错觉图和错觉图在O2上面诱发出的P100波幅、在T3上面诱发出P200波幅有显著差异.结论 视错动觉发生在初级视皮层,可能和知觉组织方式相关.     

Perception of the cabin attitude changes in hypergravity

BACKGROUND: The G-excess illusion is becoming increasingly recognized as a cause of aviation fatalities. Studies of this illusion have looked at perception of subjects' orientation by moving the head during hypergravity, but independent of the pilot's head movement with respect to aircraft. This illusion can also occur by aircraft motion, but this has not been studied extensively. OBJECTIVE: The aim of this study was to investigate the subject's perception of orientation to the simulator cab attitude changes at 1.6 G without making any head movement with respect to the cab, and assess the feasibility of simulating the G-excess illusion on the ground with a centrifuge-like spatial disorientation simulator. METHODS: The 1.6-G force field was provided by the gravitoinertial force (GIF) of the simulator when it made an off-center (planetary) rotation at a constant velocity of 130 degrees x s(-1). Eleven subjects' perceptions of orientation of the cab attitudes were collected respectively by their report before and after certain cab tilt, in a roll plane of 1.6 G. RESULTS: When the cab was tilted 20 degrees at 1.6 G, the subjects perceived the angle to be 48.6 +/- 39.4 degrees. CONCLUSION: Most subjects experienced an exaggerated sensation to the cab attitude changes in roll plane. G-excess illusion can be generated in a centrifuge-like device on the ground.     

Visual scene effects on the somatogravic illusion.

This study attempted to determine which visual scene cues are most effective in overcoming the somatogravic illusion (SGI), a form of spatial disorientation that occurs when a shift in the resultant gravitoinertial force vector created by a sustained linear acceleration is misinterpreted as a change in pitch or bank attitude. Nine subjects were exposed to a gravitoinertial force shift of -30 degrees in the pitch plane, both with their eyes closed and while viewing computer-generated visual scenes through a wide field-of-view head-mounted display. The scenes depicted acceleration over a shoreline by means of horizon, texture, perspective, and color cues that were presented both in isolation and in various combinations. None of the scenes significantly reduced the magnitude of the SGI relative to the eyes-closed (baseline) pitch illusion, even though the textured scenes produced some linear vection. It remains to be established whether low-cost head-mounted visual displays can reliably reduce the magnitude of the SGI and other spatially disorienting illusions.     

空军飞行员飞行错觉后反应分析

目的 掌握现阶段空军飞行员发生飞行错觉后反应状况,以期制定相应对策. 方法 运用"飞行错觉水平量表"对来院疗养的1275名空军飞行员进行飞行错觉问卷调查. 结果 有效量表1221份,飞行错觉总发生率为91.5%,发生错觉后看仪表不能克服的占8.1%,发生错觉后影响操纵的占32.7%,发生了错觉不知道的占6.9%,发生错觉后不能识别周围环境的占1.4%,出现不适症状的占56.6%.歼击机、强击机飞行员飞行错觉后的反应水平明显高于其他机种(P＜0.05).结论 空军飞行员飞行错觉后反应影响飞行安全,急待建立飞行错觉系统训练体系,减少飞行错觉后反应发生,降低飞行错觉反应水平. Abstract： Objective To investigate the Air Force pilots' response to the flight illusion for finding countermeasures. Methods A questionnaire entitled" the level scale of flight illusion" was inquired from 1275 pilots. Results The incidence of flight illusion was 91. 5% by analyzing 1221applicable replies. Among which even 8. 1% pilots could not overcome the illusions by observing instruments. 32.7% pilots reported illusion caused difficulties on aircraft control while 6.9% and 1.4% pilots respectively showed unawareness of illusion and lost the awareness of environment when illusion happened. 56. 6% pilots appeared discomfort. Fighter and attacker pilots showed stronger response than the other type of aircrafts' (P＜0.05). Conclusions Pilot's negative responses to flight illusions have effectively influenced flight safety. It is suggested to build up corresponding training system to control the pilot's negative response to flight illusions.     

短臂离心机不同转速暴露时飞行员前庭性错觉及前庭自主神经反应对比

目的 观察飞行员短臂离心机不同转速暴露时前庭性错觉诱发效果及前庭自主神经反应情况,寻求利用短臂离心机进行前庭性错觉地面模拟训练时的合适转速. 方法 90名健康歼击机飞行员根据不同离心机转速（21、30、37 r/min）分为3组,每组30人.参考电动转椅的前庭性错觉模拟训练方案,采用适合短臂离心机运行特点的前庭性错觉诱发方法,在SAC-Ⅲ型短臂离心机上进行反旋转错觉及科里奥利错觉模拟.每组仅进行1个转速下的错觉模拟.对比不同转速下飞行员错觉诱发情况及前庭自主神经反应情况. 结果 ①离心机不同转速时飞行员反旋转错觉、科里奥利翻转错觉（包括头右旋及左旋时）及科里奥利旋转错觉（包括头前倾和回靠时）的诱发率差异均有统计学意义（X2 ＝6.477～20.000,P＜0.01或P＜0.05）.21 r/min暴露时的诱发率低于30 r/min和37 r/min暴露时（x2＝0.073～0.351,P＞0.05）.②3种转速下,离心机反旋转错觉形态表现相同,但错觉强度随离心机转速加快而增强.科里奥利翻转错觉形态表现稳定,3种转速下其表现分布差异无统计学意义（（x2＝0.090、0.056,P＞0.05）.科里奥利旋转错觉形态表现较为多样,3种转速下头前倾时错觉形态表现分布差异无统计学意义（X2＝1.810,P＞0.05）;头回靠时错觉发生例数较少,未行统计学处理.③3种转速下前庭自主神经反应评分分值随转速增加而增高,且差异有统计学意义（F＝ 15.058,P＜0.01）;37 r/min暴露时的分值明显高于21 r/min和30 r/min暴露时（P＜0.01或P＜0.05）;30 r/min与21 r/min暴露时的分值差异无统计学意义（P＞0.05）. 结论 臂长2 m的短臂离心机上以30 r/min暴露时,飞行员前庭性错觉的诱发率较高,且前庭自主神经反应较轻,此转速用于飞行人员前庭性错觉的地面模拟训练较为合适.     

Localization of virtual sound at 4 Gz

INTRODUCTION: Acceleration directed along the body's z-axis (Gz) leads to misperception of the elevation of visual objects (the "elevator illusion"), most probably as a result of errors in the transformation from eye-centered to head-centered coordinates. We have investigated whether the location of sound sources is misperceived under increased Gz. METHOD: Visually guided localization responses were made, using a remotely controlled laser pointer, to virtual auditory targets under conditions of 1 and 4 Gz induced in a human centrifuge. As these responses would be expected to be affected by the elevator illusion, we also measured the effect of Gz on the accuracy with which subjects could point to the horizon. RESULTS: Horizon judgments were lower at 4 Gz than at 1 Gz, so sound localization responses at 4 Gz were corrected for this error in the transformation from eye-centered to head-centered coordinates. We found that the accuracy and bias of sound localization are not significantly affected by increased Gz. CONCLUSION: The auditory modality is likely to provide a reliable means of conveying spatial information to operators in dynamic environments in which Gz can vary.     

Formation of images of spatial position during the development of illusions of vestibular origin

This paper discusses specific features of pilot's spatial orientation in response to spatial illusions of vestibular origin associated with their recognition and management. Analysis of data in the literature and observations by the present authors allow the conclusion that pilot's spatial orientation, once spatial illusions have emerged, makes him assess not only the instrumental information but also the pattern of his own controlling movements. As a consequence, it is suggested that in relation to the formation of a correct image of spatial position (particularly in the case of spatial illusions) pilot's controlling movements act as part of instrumental information concerning the spatial position of the flying vehicle.     

Joint coordination in young and older adults during quiet stance: effect of visual feedback of the center of pressure

How aging affects body sway and joint coordination during quiet standing was investigated under two visual feedback conditions provided on a monitor screen: fixed and moving cursor representing the center of pressure (COP) position measured by a platform. The across-time joint motion variance of ankle, knee, hip, mid-trunk, and cervical spine leading to COP displacement was analyzed using the uncontrolled manifold approach. The body sway was assessed by the COP displacement. Young and older adults showed greater ankle joint contribution to COP displacement than the other joints. However, older adults showed larger variability of knee and mid-trunk joint motions than young adults. During the moving condition, the ankle joint contribution decreased and hip joint contribution increased for both groups, but the COP displacement increased only for the older adults. We conclude that joint coordination and body sway during quiet standing can be modified by providing COP visual feedback and that joint coordination is affected by aging.     

航天失重环境对空间定向的影响

在航天医学的研究中，对于在失重条件下空间定向特别是视觉空间定向变化的研究还较少。本文总结了航天失重环境下的空间定向障碍类型，并简介了一个用于研究航天失重环境下感觉线索相互作用的矢量模型。     

Perception of haptic motion is enhanced during conditions of increased postural stability

BackgroundCoupling between postural sway and fingertip displacement has been observed in individuals lightly touching a moving surface. This can be attributed to the central nervous system (CNS) misinterpreting surface motion as self-motion, evoking a compensatory sway response.Research questionDoes baseline postural state influence the correct perception of haptic object motion?MethodsMotion perception detection thresholds of index finger displacement at 1 mm s⁻¹ velocity during light touch were determined for three postural conditions: standing with eyes open (EO) and closed (EC), and sitting with eyes closed. For the standing condition with eyes shut, displacement thresholds were measured using three velocities (1, 2 and 4 mm s⁻¹).ResultsPostural condition had a large influence on motion perception, with a reduction in displacement threshold from 12 → 6 → 2 mm during the transition from standing EC → standing EO → sitting EC. A systematic decrease in displacement perception threshold was observed with increasing velocity. This tends to suggest that the increase of the touched object velocity may help overcoming the misinterpretation.SignificanceThese results suggest that the ability to disambiguate self motion from haptic motion is enhanced during stable postures, and when stimulus velocity is high. Our findings may help to understand the mechanisms underlying the coupling between surface movements and postural sway, reported in the literature.     

The assessment of body sway and the choice of the stability parameter(s)

This methodological study aims at comparison of the practical usefulness of several parameters of body sway derived from recordings of the center of pressure (CoP) with the aid of a static force platform as proposed in the literature. These included: mean displacement velocity, maximal range of movement along x- and y-co-ordinates, movement area, planar deviation, phase plane parameter of Riley and the parameters of the diffusion stabilogram according to Collins. They were compared in over 850 experiments in a group of young healthy subjects (n = 10, age 21-45 years), a group of elderly healthy (n = 38, age 61-78 years) and two groups of elderly subjects (n = 10 and n = 21, age 65-89 years) with stability problems under different conditions known to interfere with stability as compared to standing with open eyes fixing a visual anchoring point: closing the eyes, standing on plastic foam in stead of a firm surface and performing a cognitive task: the modified stroop test. A force platform (Kistler) was used and co-ordinates of the body's center of pressure were recorded during 60 s of quiet barefoot standing with a sampling frequency of 10 Hz. In general, the results show important overlapping among groups and test conditions. Mean displacement velocity shows the most consistent differences between test situations, health conditions and age ranges, but is not affected by an extra cognitive task in healthy old people. Mean maximal sideways sway range is different among groups and test conditions except for the cognitive task in young and elderly subjects. Standardised displacement parameters such as standard deviations of displacements and planar deviation discriminate less well than the actual range of motion or the velocity. The critical time interval derived from the diffusion stabilogram according to Collins et al. seems to add a specific type of information since it shows significant influence from addition of a cognitive task in old subjects standing on a firm surface but not when standing on plastic foam. The critical time interval shows no consistent relation to any other parameter. The influence of cognitive activity on balance merits further exploration. A new parameter, sum of maximal deviation time (SDT) was proposed showing complete discrimination between frail elderly and other old subjects when obtained while visual input was suppressed. It was concluded that mean displacement velocity seems to be the most informative parameter in most situations.     

Effect of seating, vision and direction of horizontal oscillation on motion sickness

BACKGROUND: Low frequency horizontal oscillation can cause motion sickness in some forms of transport, but the influence of the characteristics of the motion and the visual and postural conditions of the body on sickness are not known. HYPOTHESES: It was hypothesised that body position, vision and direction of motion will have an effect on motion sickness. METHOD: There were 72 seated subjects who were exposed to horizontal oscillation at 0.25 Hz, 0.7 ms(-2) r.m.s. (peak-to-peak displacement of 0.8 m) for up to 30 min while in 1 of 6 conditions. Three conditions involved fore-and-aft motion and three involved lateral motion. For motion in each axis, subjects sat within a closed cabin with either: a) a high backrest with their eyes open; b) a low backrest with their eyes open; or c) a low backrest with their eyes closed and blindfolded. Subjects provided ratings of their motion sickness symptoms at 1-min intervals during the 30-min exposures. RESULTS: The most nauseogenic stimulus was fore-and-aft motion with a low backrest and the eyes open. Self-ratings of motion sickness susceptibility provided by subjects before participating in the experiment were positively correlated with their illness ratings during the experiment. CONCLUSIONS: Restraint to the upper body during exposure to horizontal acceleration may reduce the susceptibility to motion sickness caused by horizontal oscillation. The relative nauseogenicity of fore-and-aft and lateral oscillation depends on the support given to the upper body. In the conditions of the experiment the effects of the postural support given to the subjects and their prior susceptibility to motion sickness were greater than any effect of the visual conditions.     

Effects of gravitoinertial force variations on optokinetic nystagmus and on perception of visual stimulus orientation.

Recordings of horizontal and vertical eye movement were obtained with subjects exposed to vertical, horizontal, and oblique optokinetic stimulation during parabolic flight. When the optokinetic stimulation was vertical, the upward slow phase eye velocity increased during transition from high force level to free-fall, and decreased during transition from free-fall to high force level. During optokinetic stimulation in the horizontal and oblique plane, the gravitoinertial forces of parabolic flight induced changes in the velocity of the vertical component of the eye movements, and, therefore, changes in the plane of the eye movements. Some subjects also perceived modifications in the apparent orientation of the visual motion. These findings are in agreement with previous observations on the presence of a vertical nystagmus induced by changes in plane vertical acceleration. They also suggest a close interaction of reflexive eye movements induced by graviceptor inputs and visual inputs for visual stabilization during variations of gravitoinertial force level.     

Spin-echo M-mode NMR imaging.

A nuclear magnetic resonance (NMR) imaging and display method for the observation of the continuous motion of objects is presented. By modifying a line scan technique, the spin-density distribution along a line is displayed in succession. Although spatial information is limited to only one dimension, the motion of the object is recorded at intervals of 55 ms by using a commercially available NMR imaging system. In a phantom study, this method yielded accurate velocity measurements along a single axis. When the method was applied to the human chest, an image analogous to that of M-mode echocardiography was obtained. This method, which can be called spin-echo M-mode NMR imaging, approaches the functional analysis of cardiac wall motion in regions where echocardiography is not possible. The effects of respiratory motion on the left ventricular wall were recorded in addition to its intrinsic contractile motion in an image obtained along a line parallel to the cranio-caudal axis of the body. The advantages of this method to assess cardiac wall motion in a patient with an arrhythmia were also demonstrated.     

The effects of acoustic orientation cues on instrument flight performance in a flight simulator

An initial version of an acoustic orientation instrument (AOI), in which airspeed was displayed as sound frequency, vertical velocity as amplitude modulation rate, and bank angle as right-left lateralization, was evaluated in a T-40 (Link GAT-3) motion-based simulator. In this study, 15 pilots and 3 non-pilots were taught to use the AOI and flew simulated flight profiles under conditions of neither visual nor auditory instrumentation (NO INPUT), AOI signals only (AOI), T-40 simulator instrumentation only (VISUAL), and T-40 simulator instrumentation with AOI signals (BOTH). Bank control under AOI conditions was significantly better than under the NO INPUT condition for all flying tasks. Bank control under VISUAL conditions was significantly better than under the AOI condition only during turning and when performing certain complex secondary tasks. The pilots' ability to use the AOI to control vertical velocity and airspeed was less apparent. However, during straight-and-level flight, turns, and descents the AOI provided the pilots with sufficient information to maintain controlled flight. Factors of potential importance in using sound to convey aircraft attitude and motion information are discussed.     

On the physics of momentum in ballistics: Can the human body be displaced or knocked down by a small arms projectile?

Shooting incidents are often portrayed as resulting in a sometimes violent backwards displacement of the victim. This opinion is also not infrequently held by expert witnesses. The physical force responsible for this would be momentum (mass x velocity). The physics of momentum in ballistic injury is explained in detail. The maximum momentum transferred from different small arms projectiles including large calibre rifles and a 12-gauge shotgun only results in a backwards motion of a 80 kg target body of 0.01–0.18 m/s, which is negligible compared to the velocity of a pedestrian (1–2 m/s). Furthermore, counterbalance is constantly maintained by neurophysiological reflexes. So the effect of the momentum transferred from the missile is virtually zero and there is no backwards motion of the person shot. Empirical evidence verifying these calculations can be obtained from hunting big game, from human gunshot victims and from a video documentary demonstrating the lack of any backwards motion of a person wearing body armour after hits from a centre fire rifle. So the alleged backwards hurling of a person shot is nothing but a myth which should be refuted not only because it is incorrect but also because it can result in miscarriages of justice.