空間識・シリーズ教育講座 １２．能動と受動の知覚・動作―福田精先生の疑問―

Motion sickness is defined as a sensation of uneasiness that occurs during physical motion, such as transportation by bus, plane, car or train. Postural control is one of the multisensory processes that has been examined in individuals susceptible to motion sickness. Indeed, postural control relies on visual, somatosensory and vestibular information. While studies suggest normal-like postural control during quiet standing, others suggest that individuals with motion sickness show increased postural instability during sensory perturbations, namely during visual and somatosensory disturbances. The impact of vestibular stimulation on postural control in individuals with motion sickness has yet to be determined. Therefore, the aim of the present exploratory study was to examine the effects of sinusoidal electrical vestibular stimulation on postural control in individuals with varying degrees of motion sickness. Fifty participants were divided into three groups based their susceptibility to motion sickness. Participants were initially tested at baseline in the four postural conditions of the modified Clinical Test of Sensory Integration and Balance protocol (mCTSIB): eyes open on firm surface, eyes closed on firm surface, eyes open on foam surface, eyes closed on foam surface. These four conditions were then repeated during sinusoidal electrical vestibular stimulation (EVS) of 1mA at 1Hz. In baseline conditions, no significant group differences in postural control were found. Data in experimental (EVS) conditions, however, suggests that individuals with high susceptibility to motion sickness are more impacted by vestibular stimulation, specifically in the eyes closed on firm surface condition. It has been suggested that motion sickness could be the result of an altered multisensory integration process. While the present data do not allow us to answer this question, it would remain important to examine all types of sensory perturbations and combinations thereof in a larger group of individuals.

Analysis of driver's head tilt using a mathematical model of motion sickness

ObjectiveEasily available clinical tests to evaluate postural control are needed. Furthermore, motion sickness (MS) and postural control are correlated. The aims of this study were to compare the internal validity of a set of clinical tests of postural control with the internal validity of static posturography and to evaluate possible associations between postural control and MS. MethodsWe included healthy subjects from a primary school in Denmark who completed questionnaires about MS and underwent two rounds of clinical tests of postural control and static posturography using a Tetrax Interactive Balance System two weeks apart. For clinical tests of postural control, subjects were observed for up to 30 s standing on both legs, on one leg, on a pillow both with their eyes open and again with their eyes closed. ResultsTwenty-one subjects were included: 71% males with an average age of 13.7 years. Agreement rates ranged from 62% to 95% between test and retest in clinical tests.; lowest for subjects standing on their non dominant leg with their eyes open and highest for subjects performing Romberg's test with their eyes closed along with subjects standing on a pillow with their eyes open. For several of these tests, almost all subjects were able to hold their balance for the full 30 s. Test-retesting using static posturography by Bland Altman plot showed datapoints scattered equally above and below the mean line indicating no systematic bias. Results of clinical tests and static posturography were not associated. MS was reported from 43% of subjects and a trend was observed with high sway scores from subjects suffering from MS. This was statistically insignificant. ConclusionsDue to a ceiling effect, subjects achieved the same scores in both rounds of testing in several of the clinical tests, reducing the clinical importance of these tests. Compared to clinical tests, static posturography seemingly remains the superior method when it comes to evaluation of postural control, although not as easily applicable in a daily clinical setting. When comparing MS and postural control a trend was observed, indicating higher sway scores in subjects suffering from MS.

We observed locomotion and motion sickness in 10 normal adults wearing reversing goggles while moving outdoors. Horizontal reversal of the visual field produced moderate to severe ataxia and motion sickness in all subjects except one. There was marked variability in the sensitivity among different subjects. In contrast, vertical reversal produced no symptoms. Confusion of information relation to spatial orientation possibly caused both the motion sickness and abnormal locomotion. Horizontal reversal of visual information produces disorientation because visual information is equal in importance to that from the semicircular canals. In the case of vertical reversal of visual information, orientation may be assured by gravity. The present study suggests that motion sickness is a biological signal alerting the organism to loss of spatial orientation rather than a mere autonomic symptom produced by mismatched sensory information. It appears that motion sickness is accompanied by dysequilibrium and abnormality of locomotion.

Mitigating motion sickness with non-invasive cortical vestibular brain stimulation (vBS) is promising because it does not require redesigning VR content or altering the motion profile of a moving platform. Instead, it aims to enhance individuals' intrinsic resistance to motion sickness. However, the mechanism underlying its online efficacy remains unclear (Here, "online efficacy" means the observed motion sickness reduction during vBS not before or after vBS). Motivated by lower motion sickness susceptibility observed in congenital nystagmus patients, we hypothesized that reductions in motion sickness under vBS condition are associated with increased eye movement instability. Leveraging sham-controlled, sex-balanced eye-tracking data from an open-access database, this study presents the first evaluation of a 20 Hz-vBS approach targeting the vestibular cortices as a countermeasure to motion sickness, using spatiotemporal eye movement metrics derived from eye-tracking data collected in VR. Results show that reduced motion sickness under active vBS indeed increased eye movement instability temporarily and spatially, compared to sham vBS. We also found that the temporal metrics was more strongly associated with female participants, whereas the spatial metric was more strongly associated with male participants.

We exposed standing men and women to motion relative to the illuminated environment in a moving room. During room motion, we measured the kinematics of standing body sway. Participants were instructed to discontinue immediately if they experienced any symptoms of motion sickness, however mild. For this reason, our analysis of body sway included only movement before the onset of motion sickness. We analyzed the spatial magnitude of postural sway in terms of the positional variability and mean velocity of the center of pressure. We analyzed the multifractality of postural sway in terms of the width of the multifractal spectrum and the degree of multiplicativity of center of pressure positions. Results revealed that postural sway differed between participants who later reported motion sickness and those who did not, replicating previous effects. In a novel effect, postural responses to motion of the illuminated environment differed between women and men. In addition, we identified statistically significant interactions that involved both Sex and motion sickness status. Effects were observed separately in the spatial magnitude and multifractality of sway. The results were consistent with the postural instability theory of motion sickness (Riccio and Stoffregen in Ecol Psychol 3:195-240, 1991) and suggest that Sex differences in motion sickness may be related to Sex differences in the control and stabilization of bodily activity.

Human passive motion during boat, car or airplane travel may trigger motion sickness. Seasickness is the most provoking manifestation of motion sickness. It imposes major constraints on quality of life and human performance. Based on seasickness susceptibility the population is usually categorized into susceptible (S) and non-susceptible (NS). During repeated exposure some susceptible individuals undergo habituation and obtain symptoms relief, reflecting a third group of habituating (H) individuals. Recently, accumulative evidence suggests that the vestibular time constant (Tc) is associated with motion sickness susceptibility and attenuation of symptoms. These studies demonstrated that repeated passive motion stimuli lead to temporary short-term (days) changes in Tc, whereas sea sickness habituation process lasts 3 to 6months. Therefore, the goal of the present study was to examine the behavior of Tc during the entire span of the seasickness habituation process between the H, S and NS groups to find an objective test for seasickness severity prediction. Tc of 30 subjects was prospectively evaluated pre, 3 and 6months post exposure to sea environment using a computerized rotatory chair system protocol. Seasickness severity was evaluated by Wiker questionnaire. Significantly shorter Tc was found in the S group compared with the NS and H groups. Further analysis revealed lower maximal Slow Phase Velocity (mSPV) and nystagmus frequency (total number of beats/second) in the S group. Our results suggest that Tc, mSPV and nystagmus frequency might serve as a prediction for seasickness severity. This study was retrospectively registered on December 7th 2022 and assigned the identifier number NCT05640258.

Habituation to motion has therapeutic applications for motion sickness desensitization and rehabilitation of patients with vestibular disease. Less attention has been devoted to the opposite process: sensitization. Subjects (N = 50) were randomly allocated to four sequences: Baseline visual stimulus; then 15 min of time gap; cross-coupled motion (C-C) or a Control condition; then a time gap of 15 min or 2 h; then a retest visual stimulus. Motion exposures were for 10 min or until moderate nausea, whichever was sooner. The visual stimulus was a scene rotating in yaw at 0.2 Hz with superimposed "wobble". C-C was whole-body rotation on a turntable with eight 45° head tilts during each 30-s period. Control was head tilt without rotation. Rotational velocity was incremented in staircase steps of 3° · s-1 every 30 s. Groups were equivalent for Total Motion Sickness Symptom scores elicited by the first visual stimulus (combined: mean ± SD 10.8 ± 8.4). C-C produced greater Total Symptoms (20.3 ± 6.8) than Control (3.1 ± 3.7). Subjects recovered subjectively from C-C before retest of visual stimulus. For the retest visual stimulus, Total Symptoms were higher following C-C (15.1 ± 9.0) than following Control (8.3 ± 7.1) for both the 15 min and 2 h retests. Sickness ratings (SR) mirrored these effects of C-C. C-C motion sensitized subsequent responses to visual stimulation up to 2 h later. Sensitization of visual stimulation crossed modalities and appeared subconscious since it occurred despite subjective recovery from C-C. For some individuals, a previously relatively innocuous visual stimulus became nauseogenic on retest. The results have implications for the use of visual technologies within hours of exposure to provocative motion. Golding JF, Alund D, Gresty MA, Flynn MB. Sensitization of visually induced motion sickness by prior provocative physical motion. Aerosp Med Hum Perform. 2024; 95(10):741-748.

PURPOSE: This study aimed to investigate whether long-term Tai Chi (TC) practice could lower fall risks in older adults during stair descent under dual-task (DT) conditions. This setting combines cognitive and physical demands and is associated with an increased risk of falls. We compared the stair descent patterns of TC practitioners and non-exercising (NE) participants to assess stability and fall risk. METHODS: A total of 30 older participants (including 15 TC practitioners with at least 10 years of experience and 15 NEs), descended a six-step staircase under single-task (ST) and DT conditions. Kinematic and kinetic data were collected using an eight-camera motion analysis system and two force plates embedded in the stairs. Key variables analyzed included walking velocity, foot clearance, head and trunk tilt angles, and the center of mass-center of pressure (COM-COP) inclination angle in the anteroposterior and mediolateral directions. Statistical analyses included a mixed model two-way ANOVA to examine group and task condition effects, with Bonferroni-adjusted post-hoc tests conducted for significant interactions. RESULTS: TC practitioners exhibited a smaller reduction in walking velocity (p = 0.016, η2p = 0.226) and greater foot clearance (p = 0.031, η2p = 0.187). They also showed smaller trunk (p = 0.041, η2p = 0.169) and head tilt angles (p = 0.002, η2p = 0.340), indicating a more upright posture. Additionally, TC practitioners had significantly lower center of mass-center of pressure (COM-COP) inclination angles in both the anteroposterior (p = 0.026, η2p = 0.198) and mediolateral (p = 0.005, Cohen’d = 0.297) directions. CONCLUSIONS: Although both groups of participants adopted a more cautious gait strategy under dual-task (DT) conditions, TC practitioners were less influenced by the DT paradigm compared to their NE counterparts. Our observations indicate that TC practitioners exhibit a reduced risk of falls during stair descent under DT conditions. These findings suggest that TC practitioners employ a more stable and cautious gait strategy when faced with DT conditions, thereby minimizing instability.

This chapter begins with an overview of the vestibular system. It then discusses visual acuity and the vestibulo-ocular reflex, the air-righting reflex in the cat, post-rotational reactions, positional alcohol nystagmus, motion sickness, vection illusions, the subjective visual vertical, adaptive plasticity, path finding and spatial orientation, and postural control. Many functions involve the cooperation of vestibular, visual, and somatosensory/proprioceptive inputs. One becomes aware of vestibular and other proprioceptive sensations only when they are in conflict with vision or the expectations arising from past experience. The vestibular system contributes to several levels of nervous function, including reflexes designed to keep vision clear during head motion or to maintain blood pressure when one quickly goes from a supine to an erect posture, more complicated strategies required in maintaining an upright posture, and higher perceptual functions involved in our conscious awareness of our position in our environment and our ability to navigate through it.

Background:Compensatory ocular counter-torsion (COCT) is supposed to maintain the eyes aligned with the visual environment following head tilt. Because of some recent controversies the functional capacity of this phenomenon was defined according to the extent of induced astigmatic axis error following head tilt.Materials and Methods:Objective autorefractometry was performed on 70 eyes with a regular astigmatism of ≥2D at vertical, right head tilt and left head tilt positions of 5°, 10°, 15°, 20° and 25°. Astigmatic axis error was calculated according to the difference between the defined axis at each tilted head position and the defined axis at the vertical head position. A tiltometer was used for this purpose to show the angle of head tilt without disturbing the process of refractometry.Results:The mean astigmatic axis error was 3.2° ± 1.5° and 18.4° ± 4.2° at the head tilt angles of 5° and 25° respectively. The mean percentage of tilt angle compensation by COCT was 36% and 26% at the head tilt angles of 5° and 25° respectively. There was a direct relation between the head tilt angle and the induced astigmatic axis error (ANOVA, P < 0.001, 95% of confidence interval [CI]). Astigmatic axis error values at right head tilt were significantly lower than their corresponding values at left head tilt (ANOVA, P = 0.04 95% CI).Conclusion:Any minimal angle of head tilt may cause erroneous measurement of astigmatic axis and should be avoided during refraction. One cannot rely on the compensatory function of ocular counter-torsion during the refraction.

Motion sickness adversely affects military air and sea operations. Medications help prevent motion sickness but are frequently associated with side effects. Better medications or combinations of medications are needed. Dextroamphetamine has documented anti-motion sickness effects but also has a potential for abuse. Modafinil is a relatively new central nervous system stimulant that has none of the drawbacks of dextroamphetamine, but has not been evaluated for the treatment of motion sickness. This double-blind, placebo-controlled study evaluated the anti-motion sickness efficacy of modafinil, alone or in combination with oral scopolamine. Moderate nausea was induced via a Coriolis cross-coupling stimulus. There were 60 participants who were assigned randomly to 1 of 3 conditions: 1) 2 placebo pills (DP); 2) modafinil plus placebo (MP); or 3) modafinil plus oral scopolamine (MS). The primary measure of drug efficacy was the number of head tilts tolerated upon reaching moderate nausea for 1 min without abatement. The combination of modafinil and scopolamine (MS) allowed subjects to tolerate significantly more head tilts than placebo, but modafinil alone (MP) failed to differ significantly from placebo (DP). No significant cognitive performance decrements were observed among the three experimental conditions. Modafinil was not found to be more effective than placebo. Further testing is recommended to determine whether the potentially promising combination of modafinil and scopolamine provides better efficacy or fewer side effects than scopolamine administered alone.

Effects of Immersive Virtual Reality Headset Viewing on Young Children: Visuomotor Function, Postural Stability, and Motion Sickness

"Motion sickness" is the general term describing a group of common nausea syndromes originally attributed to motion-induced cerebral ischemia, stimulation of abdominal organ afferents, or overstimulation of the vestibular organs of the inner ear. Seasickness, car sickness, and airsickness are commonly experienced examples. However, the identification of other variants such as spectacle sickness and flight simulator sickness in which the physical motion of the head and body is normal or even absent has led to a succession of "sensory conflict" theories that offer a more comprehensive etiologic perspective. Implicit in the conflict theory is the hypothesis that neural and (or) humoral signals originate in regions of the brain subserving spatial orientation, and that these signals somehow traverse to other centers mediating sickness symptoms. Unfortunately, our present understanding of the neurophysiological basis of motion sickness is incomplete. No sensory conflict neuron or process has yet been physiologically identified. This paper reviews the types of stimuli that cause sickness and synthesizes a mathematical statement of the sensory conflict hypothesis based on observer theory from control engineering. A revised mathematical model is presented that describes the dynamic coupling between the putative conflict signals and nausea magnitude estimates. Based on the model, what properties would a conflict neuron be expected to have?

Motion sickness is one of the most commonly seen discomforts among people that has spread across all age groups and has been affecting people since centuries. It is a phenomenon of sensory conflict between the visual, vestibular and motor system. Visually Induced motion sickness is a sub-type of motion sickness, where the brain interprets sensory messages regarding movement of eyes with respect to the body as inharmonious. Any deviation from the healthy state seen after the exposure to the virtual environment is considered as the symptom of Visually Induced Motion sickness. Nausea is the most disturbing symptom seen in this condition. Along with cold sweating, drowsiness, retching, or vomiting, dizziness or vertigo etc. This phenomenon can be homoeopathically explained as per the classification of diseases by Samuel Hahnemann in different levels. This review summarizes theories behind the causation of visually induced motion sickness, the Homoeopathic basis of its cause and the treatment protocol behind it including a few remedies and Rubrics that may help in clinical practice for the selection of the similimum. Keywords: Visually Induced motion sickness, Homoeopathy, Virtual reality, Cyber-sickness, Simulator sickness