The (in)effectiveness of anticipatory vibrotactile cues in mitigating motion sickness.

The introduction of (fully) automated vehicles has generated a re-interest in motion sickness, given that passengers suffer much more from motion sickness compared to car drivers. A suggested solution is to improve the anticipation of passive self-motion via cues that alert passengers of changes in the upcoming motion trajectory. We already know that auditory or visual cues can mitigate motion sickness. In this study, we used anticipatory vibrotactile cues that do not interfere with the (audio)visual tasks passengers may want to perform. We wanted to investigate (1) whether anticipatory vibrotactile cues mitigate motion sickness, and (2) whether the timing of the cue is of influence. We therefore exposed participants to four sessions on a linear sled with displacements unpredictable in motion onset. In three sessions, an anticipatory cue was presented 0.33, 1, or 3 s prior to the onset of forward motion. Using a new pre-registered measure, we quantified the reduction in motion sickness across multiple sickness scores in these sessions relative to a control session. Under the chosen experimental conditions, our results did not show a significant mitigation of motion sickness by the anticipatory vibrotactile cues, irrespective of their timing. Participants yet indicated that the cues were helpful. Considering that motion sickness is influenced by the unpredictability of displacements, vibrotactile cues may mitigate sickness when motions have more (unpredictable) variability than those studied here.

Self-motion perception without sensory motion.

Various studies have demonstrated a role for cognition on self-motion perception. Those studies all concerned modulations of the perception of a physical or visual motion stimulus. In our study, however, we investigated whether cognitive cues could elicit a percept of oscillatory self-motion in the absence of sensory motion. If so, we could use this percept to investigate if the resulting mismatch between estimated self-motion and a lack of corresponding sensory signals is motion sickening. To that end, we seated blindfolded participants on a swing that remained motionless during two conditions, apart from a deliberate perturbation at the start of each condition. The conditions only differed regarding instructions, a secondary task and a demonstration, which suggested either a quick halt ("Distraction") or continuing oscillations of the swing ("Focus"). Participants reported that the swing oscillated with larger peak-to-peak displacements and for a longer period of time in the Focus condition. That increase was not reflected in the reported motion sickness scores, which did not differ between the two conditions. As the reported motion was rather small, the lack of an effect on the motion sickness response can be explained by assuming a subthreshold neural conflict. Our results support the existence of internal models relevant to sensorimotor processing and the potential of cognitive (behavioral) therapies to alleviate undesirable perceptual issues to some extent. We conclude that oscillatory self-motion can be perceived in the absence of related sensory stimulation, which advocates for the acknowledgement of cognitive cues in studies on self-motion perception.

How feelings of unpleasantness develop during the progression of motion sickness symptoms.

To mitigate motion sickness in self-driving cars and virtual reality, one should be able to quantify its progression unambiguously. Self-report rating scales either focus on general feelings of unpleasantness or specific symptomatology. Although one generally feels worse as symptoms progress, there is anecdotal evidence suggesting a non-monotonic relationship between unpleasantness and symptomatology. This implies that individuals could (temporarily) feel better as symptoms progress, which could trouble an unambiguous measurement of motion sickness progression. Here we explicitly investigated the temporal development of both unpleasantness and symptomatology using subjective reports, as well as their mutual dependence using psychophysical scaling techniques. We found symptoms to manifest in a fixed order, while unpleasantness increased non-monotonically. Later manifesting symptoms were generally judged as more unpleasant, except for a reduction at the onset of nausea, which corresponded to feeling better. Although we cannot explicate the origin of this reduction, its existence is of importance to the quantification of motion sickness. Specifically, the reduction at nausea onset implies that rating how bad someone feels does not give you an answer to the question of how close someone is to the point of vomiting. We conclude that unpleasantness can unambiguously be inferred from symptomatology, but an ambiguity exists when inferring symptomatology from unpleasantness. These results speak in favor of rating symptomatology when prioritizing an unambiguous quantification of motion sickness progression.

[Motion sickness in motion: from carsickness to cybersickness]. / Bewegingsziekten in beweging.

- Motion sickness is not a disorder, but a normal response to a non-normal situation in which movement plays a central role, such as car travel, sailing, flying, or virtual reality.- Almost anyone can suffer from motion sickness, as long as at least one of the organs of balance functions. If neither of the organs of balance functions the individual will not suffer from carsickness, seasickness, airsickness, nor from cybersickness. - 'Cybersickness' is a form of motion sickness that is stimulated by artificial moving images such as in videogames. Because we are now exposed more often and for longer periods of time to increasingly realistic artificial images, doctors will also encounter cases of motion sickness more often. - The basis for motion sickness is the vestibular system, which can be modulated by visual-vestibular conflicts, i.e. when the movements seen by the eyes are not the same as those experienced by the organs of balance.- Antihistamines can be effective against motion sickness in everyday situations such as car travel if taken before departure, but the effectiveness of medication for motion sickness is limited.

Perceptual scaling of visual and inertial cues: effects of field of view, image size, depth cues, and degree of freedom.

In the field of motion-based simulation, it was found that a visual amplitude equal to the inertial amplitude does not always provide the best perceived match between visual and inertial motion. This result is thought to be caused by the "quality" of the motion cues delivered by the simulator motion and visual systems. This paper studies how different visual characteristics, like field of view (FoV) and size and depth cues, influence the scaling between visual and inertial motion in a simulation environment. Subjects were exposed to simulator visuals with different fields of view and different visual scenes and were asked to vary the visual amplitude until it matched the perceived inertial amplitude. This was done for motion profiles in surge, sway, and yaw. Results showed that the subjective visual amplitude was significantly affected by the FoV, visual scene, and degree-of-freedom. When the FoV and visual scene were closer to what one expects in the real world, the scaling between the visual and inertial cues was closer to one. For yaw motion, the subjective visual amplitudes were approximately the same as the real inertial amplitudes, whereas for sway and especially surge, the subjective visual amplitudes were higher than the inertial amplitudes. This study demonstrated that visual characteristics affect the scaling between visual and inertial motion which leads to the hypothesis that this scaling may be a good metric to quantify the effect of different visual properties in motion-based simulation.

The time constant of the somatogravic illusion.

Without visual feedback, humans perceive tilt when experiencing a sustained linear acceleration. This tilt illusion is commonly referred to as the somatogravic illusion. Although the physiological basis of the illusion seems to be well understood, the dynamic behavior is still subject to discussion. In this study, the dynamic behavior of the illusion was measured experimentally for three motion profiles with different frequency content. Subjects were exposed to pure centripetal accelerations in the lateral direction and were asked to indicate their tilt percept by means of a joystick. Variable-radius centrifugation during constant angular rotation was used to generate these motion profiles. Two self-motion perception models were fitted to the experimental data and were used to obtain the time constant of the somatogravic illusion. Results showed that the time constant of the somatogravic illusion was on the order of two seconds, in contrast to the higher time constant found in fixed-radius centrifugation studies. Furthermore, the time constant was significantly affected by the frequency content of the motion profiles. Motion profiles with higher frequency content revealed shorter time constants which cannot be explained by self-motion perception models that assume a fixed time constant. Therefore, these models need to be improved with a mechanism that deals with this variable time constant. Apart from the fundamental importance, these results also have practical consequences for the simulation of sustained accelerations in motion simulators.

A re-investigation of the role of utricular asymmetries in Space Motion Sickness.

During the first days of spaceflight, about 50-70% of the astronauts experience symptoms of Space Motion Sickness (SMS). It has been proposed that an asymmetry between the left and right otolith organs contributes to an astronaut's individual susceptibility. A recently developed test to measure unilateral utricular function enabled us to re-investigate this so-called otolith asymmetry hypothesis, while using the paradigm of sustained centrifugation as a ground based model for SMS. This latter paradigm has been shown to elicit symptoms similar to those of SMS and is referred to as Sickness Induced by Centrifugation (SIC). In 15 healthy subjects unilateral utricular function was assessed by recording ocular counter rolling during a unilateral centrifugation paradigm. In addition, saccular function was assessed by recording Vestibular Evoked Myogenic Potentials (VEMPs), and horizontal semicircular canal function was assessed using bithermal caloric stimulation. SIC-susceptible subjects showed a marginally higher degree of utricular asymmetry, utricular sensitivity and semicircular canal sensitivity (p < 0.1) than the non-susceptible group. Interestingly, a logistic regression model using both utricular and semicircular canal parameters led to a correct classification of 91% of the subjects. As such, these results suggest that otolith asymmetry is at most one factor - and not present in all susceptible subjects - in defining susceptibility to SMS and SIC. Both the utricular and the canal system might be involved as well.

Susceptibility to seasickness.

This paper explains part of the observed variability in passenger illness ratings aboard ships by gender, age and sickness history. Within the framework of a European project, 2840 questionnaires, gathered on several ships operating all over Europe, were analysed. Gender, age and sickness history all had a highly significant effect on seasickness. Furthermore, these effects could be characterized by two fixed parameters describing a general age effect, a third parameter dependent on sickness history and a fourth parameter dependent on gender. Female illness ratings peaked at an age of 11 years, 1.5 times as high as male ratings, which peaked at an age of 21 years. At higher ages, illness ratings decrease to only 20% of their maximum, reducing gender differences to zero. Passengers with a previous history of seasickness rated their illness about two times higher than those who had not felt sick before.

Motion sickness and tilts of the inertial force environment: active suspension systems vs. active passengers.

BACKGROUND: Maneuvering in vehicles exposes occupants to low frequency forces (< 1 Hz) which can provoke motion sickness. HYPOTHESIS: Aligning with the tilting inertial resultant (gravity + imposed horizontal acceleration: gravito-inertial force (GIF)) may reduce motion sickness when tilting is either 'active' (self-initiated; Experiment 1) or 'passive' (suspension machinery; Experiment 2). METHODS: Exp 1: Twelve seated subjects were exposed to continuous horizontal translational oscillation through the body x-axis (3.1 m x S(-2) peak acceleration, 0.20 Hz) while making head tilts which were either aligned or misaligned (180 degrees out of phase) with respect to GIF. The two sessions were one week apart at the same time of day, counterbalanced for order. Head tilts were controlled by tracking a moving LED display and head trajectory was verified by accelerometry. Motion continued until moderate nausea was achieved (motion endpoint) or until a 30 min cut-off. Exp 2: A different group of 12 subjects were exposed to continuous horizontal translational sinusoidal oscillation through the body x-axis (2.0 m x S(-2) peak acceleration, 0.176 Hz) while seated in a cab which was tilted by suspension machinery around the y-axis of the ears so that GIF was aligned or misaligned (180 degrees out of phase) with the body z-axis. RESULTS: Exp 1: Mean +/- SD time to motion endpoint was significantly longer for aligned (19.2 +/- 12.0 min) than for misaligned (17.8 +/- 13.0 min; p < 0.05, two-tail). Exp 2: Mean +/- SD time to motion endpoint was significantly shorter for aligned (21.8 +/- 10.9 min) than for misaligned (28.3 +/- 5.8 min; p < 0.01, two-tail). CONCLUSIONS: Whether or not compensatory tilting protects against (Exp 1) or contributes to (Exp 2) motion sickness may be influenced by whether the tilting is under the active control of the person (e.g., car driver) or under external control (e.g., passenger in a high-speed tilting train).

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.

Motion sickness.

The number of recently published papers on motion sickness may convey the impression that motion sickness is far from being understood. The current review focusses on a concept which tends to unify the different manifestations and theories of motion sickness. The paper highlights the relations between ergonomic principles to minimise motion sickness and the concept predictions. The clinical management of sufferers from motion sickness in terms of selection, pharmacological measures and desensitisation courses is treated as well.

Contribution of the otoliths to the human torsional vestibulo-ocular reflex.

The dynamic contribution of the otolith organs to the human ocular torsion response was examined during passive sinusoidal body roll about an earth-horizontal axis (varying otolith inputs) and about an earth-vertical axis (invariant otolith inputs). Torsional eye movements were registered in 5 subjects by means of video-oculography. At a fixed amplitude of 25 degrees, the stimulus frequency was varied from 0.05 to 0.4 Hz. Additionally, at a fixed frequency of 0.2 Hz, the response was also measured at the amplitudes to 12.5 degrees and 50 degrees. The results showed that the gain and phase of the torsional slow component velocity (SCV) did not depend on stimulus amplitude, indicating a linear response. Contribution of the otoliths affected the ocular torsion response in three different ways. First, the gain of the SCV was slightly, but consistently, higher during rotation about an earth-horizontal axis than during rotation about an earth-vertical axis. With invariant otolith inputs the average gain increased from 0.10 at 0.05 Hz to 0.26 at 0.25 Hz. With varying otolith inputs, the average gain increased from 0.14 to 0.37. Second and more substantially, contribution of the otoliths improved the response dynamics by reducing the phase lead at frequencies up to 0.02 Hz. Third, the nystagmus showed considerably less anticompensatory saccades in upright conditions than in supine conditions, even though the SCV gain was lower in the latter. As a consequence, the average excursion of torsional eye position was highest during earth-horizontal rotation. This effect was observed in the entire frequency range. Thus, the otoliths controlled the human torsional VOR not only at low stimulus frequencies by keeping the slow component in phase with head motion, but also in a wider frequency range by modulating the saccadic behavior as to increase the amplitude of ocular torsion. We conclude that the primary concern of the otolith-oculomotor system during head tilt is to stabilize eye position in space, rather than to prevent retinal blur.

Cervically induced ocular torsion: physiological and clinical aspects.

Ocular torsion was measured in five subjects during sinusoidal lateral tilt (amplitude 25 degrees, 0.2 Hz). The cervical contribution to ocular torsion was best visible as the difference between the signals obtained in conditions with only head tilt and conditions with whole body tilt. Contribution of the neck did not affect the slow component, but produced an anticompensatory modulation of the beating field offset by means of saccades (analogous to gaze shift). Static tilt conditions (25 degrees tilt) of the trunk only, the head only or the whole body showed similar data, although of smaller amplitude. The results from patients suffering from post-whiplash syndrome were similar to those of healthy subjects, showing large intersubject variability. The reduced tolerance to head tilt of whiplash patients restricts useful implementation of this sort of test in the clinic.

Motion sickness: only one provocative conflict?

In reviewing the various forms of motion sickness, the classic sensory rearrangement theory has been redefined by demonstrating that only one type of conflict is necessary and sufficient to explain all different kinds of motion sickness. A mathematical description is provided from the summarizing statement that "All situations which provoke motion sickness are characterised by a condition in which the sensed vertical as determined on the basis of integrated information from the eyes, the vestibular system and the nonvestibular proprioceptors is at variance with the subjective vertical as expected from previous experience."

Roll motion stimuli: sensory conflict, perceptual weighting and motion sickness.

In an experiment with 17 subjects, interactions of visual roll motion stimuli and vestibular body tilt stimuli were examined in determining the subjective vertical. Interindividual differences in weighting the visual information were observed, but in general, visual and vestibular responses added in setting the vertical. Despite the conflicting sensory information, motion sickness was not reported apart from one subject on one single occasion. This is in conflict with the sensory mismatch theory on motion sickness, but in agreement with the subjective vertical conflict theory.

Motion sickness amelioration induced by prism spectacles.

A side effect of the prescription of prism glasses according to the principle of Utermöhlen to improve mechanical reading skills of certain types of learning disabled children was the alleviation of car sickness. Besides a decrease in reported symptoms after prescription of these glasses, the effect is quantified by a decrease in estimated number of emeses per year per patient. A placebo effect is unlikely because alleviation of car sickness was not the original intention of the prescription, and the symptoms returned as soon as the spectacles were discontinued.

Contributions of roll and pitch to sea sickness.

The purpose of this study was to test the traditional assumption that sea sickness is uniquely provoked by heave motion characteristics, with pitch and roll movements being ineffective. In an experiment with a ship motion simulator, subjects were exposed to pitch and roll motions in combination with rather weak heave motions that have no motion sickness-inducing potential. Very high levels of motion sickness were observed (with a motion sickness rating scale) in almost 50% of our subjects. In three control experiments, it was shown that these heave motions, when presented separately, indeed have no motion sickness-inducing potential and that pitch and roll motions presented alone or in combination with each other have only a very small motion sickness-inducing potential. These results indicate that pitch and roll when combined with small heave motions, which in themselves are not sickness provoking, produce more motion sickness than claimed by the classic models. This suggests that in models on motion sickness, pitch and roll should be combined in a nonlinear fashion with heave and that such models will remain rather crude if they do not include a description of the vestibular contribution to motion sickness.

Modelling motion sickness and subjective vertical mismatch detailed for vertical motions.

In an attempt to predict the amount of motion sickness given any kind of motion stimulus, we describe a model using explicit knowledge of the vestibular system. First, the generally accepted conflict theory is restated in terms of a conflict between a vertical as perceived by the sense organs like the vestibular system and the subjective vertical as determined on the basis of previous experience. Second, this concept is integrated with optimal estimation theory by the use of an internal model. If detailed for vertical motions only, the model does predict typical observed motion sickness characteristics, irrespective the parameter setting. By adjusting the nonvestibular parameters, the model can also quantitatively be adapted to seasickness data from the literature. With this concept, sickness severity hypothetically can also be predicted for other motions, irrespective of their origin and complexity.

A sustained hyper-g load as a tool to simulate space sickness.

In April 1989 the three European scientist astronauts of the D1 Spacelab Mission were exposed to a 1.5 hours +3G centrifuge run in supine position, resulting in a linear acceleration along the subjects' x-axis. Afterwards, severe motion sickness symptoms were provoked by head movements (Sickness Induced by Centrifugation: SIC). The astronauts mentioned close similarities with what they experienced in space during the D1-Spacelab Mission in 1985, where head movements also provoked motion sickness symptoms (Space Adaptation Syndrome: SAS). Moreover, the astronauts agreed that the rank order of their susceptibility to SAS was the same as for SIC. It was therefore postulated that with this method SAS could be simulated on earth. Additionally, in otolith function tests following the centrifuge run, changes in visual-vestibular interaction were observed, which replicated objective findings obtained with the same astronauts immediately after the D1 Spacelab Mission. During the last couple of years a series of experiments has been carried out to determine the nature of the stimulus causing SIC, the incidence of SIC, and the underlying cardio-vascular and/or vestibular mechanisms. These experiments were carried out on several astronauts and some 50 'normal' healthy subjects. In the next sections the main findings of all these experiments and the implications are summarized.