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Otolith Signal Processing and Motion Sickness
Annals of the New York Academy of Sciences
Abstract
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... The computation of this conflict vector can be simplified, if one only considers the difference between the subjective vertical and the vertical provided by the sensory signals, as proposed by the so-called subjective vertical conflict theory (47)(48)(49)(50). On first consideration, the sensory mismatch theory and the subjective vertical conflict theory appear to be equivalent, but centering the computation of the conflict on the perception of verticality has significant impact on the definition of the nauseogenity of specific stimuli. ...
... Accelerations during linear oscillations below a specific frequency are, therefore, added to gravity as the brain fails to identify them correctly and perceives an unexpected change of the gravity vector, unmatched by other sensory signals. The frequency segregation processing is also at the base of the computation of the error vector according to the subjective vertical theory (47)(48)(49)(50). To reproduce the differences between horizontal and vertical oscillations, however, the initial theory was extended including an additional internal conflict signal, specific for horizontal linear accelerations [subjective vertical-horizontal theory (SVH)] (144). ...
Motion sickness is a common disturbance occurring in healthy people as a physiological response to exposure to motion stimuli that are unexpected on the basis of previous experience. The motion can be either real, and therefore perceived by the vestibular system, or illusory, as in the case of visual illusion. A multitude of studies has been performed in the last decades, substantiating different nauseogenic stimuli, studying their specific characteristics, proposing unifying theories, and testing possible countermeasures. Several reviews focused on one of these aspects; however, the link between specific nauseogenic stimuli and the unifying theories and models is often not clearly detailed. Readers unfamiliar with the topic, but studying a condition that may involve motion sickness, can therefore have difficulties to understand why a specific stimulus will induce motion sickness. So far, this general audience struggles to take advantage of the solid basis provided by existing theories and models. This review focuses on vestibular-only motion sickness, listing the relevant motion stimuli, clarifying the sensory signals involved, and framing them in the context of the current theories.
This chapter deals first with the main characteristics of the space
environment, outside and inside a spacecraft. Then the space and
space-related (ground-based) infrastructures are described. The most
important infrastructure is the International Space Station, which holds
many European facilities (for instance the European Columbus
Laboratory). Some of them, such as the Columbus External Payload
Facility, are located outside the ISS to benefit from external space
conditions. There is only one other example of orbital platforms, the
Russian Foton/Bion Recoverable Orbital Capsule. In contrast, non-orbital
weightless research platforms, although limited in experimental time,
are more numerous: sounding rockets, parabolic flight aircraft, drop
towers and high-altitude balloons. In addition to these facilities,
there are a number of ground-based facilities and space simulators, for
both life sciences (for instance: bed rest, clinostats) and physical
sciences (for instance: magnetic compensation of gravity). Hypergravity
can also be provided by human and non-human centrifuges.
In this study we describe a new approach to relate simulator sickness ratings with the main frequency component of the simulator motion mismatch, that is, the computed difference between the time histories of simulator motion and vehicle motion, respectively. During two driving simulator experiments in the TNO moving-base driving simulator—that were performed for other reasons than the purpose of this study—we collected simulator sickness questionnaires from in total 58 subjects. The main frequency component was computed by means of the power spectrum density of the computed mismatch signal. We hypothesized that simulator sickness incidence depends on this frequency component, in a similar way as the incidence of “real” motion sickness, such as sea sickness, depends on motion frequency. The results show that the simulator sickness ratings differed between both driving simulator experiments. The experiment with its main frequency component of the mismatch signal of 0.08 Hz had significantly higher simulator sickness incidence than the experiment with its main frequency at 0.46 Hz. Since the experimental design differed between both experiments, we cannot exclusively attribute the difference in sickness ratings to the frequency component, but the observation does suggest that quantitative analysis of the mismatch between the motion profiles of the simulator and the vehicle may greatly improve our understanding of the causal mechanism of simulator sickness.
Pitch head-and-trunk movements during constant velocity rotation are a provocative vestibular stimulus that produces vertigo and nausea. When exposed to this stimulus repeatedly, motion sickness symptoms diminish as the subjects habituate. Acetylleucine is a drug that is used to treat acute vestibular vertigo. In this study, we wanted to ascertain whether this drug (a) lessened motion sickness or delayed habituation; (b) accelerated the recovery following habituation; and (c) whether changes in the subjective vertical accompanied habituation. Twenty subjects were administered acetylleucine or placebo in a double-blind study during a five-day vestibular training. Horizontal vestibulo-ocular reflex, optokinetic nystagmus, smooth pursuit, and subjective visual vertical were evaluated before, during, and up to two months after the vestibular training. Based on Graybiel's diagnostic criteria, motion sickness decreased steadily in each vestibular training session, and there was no difference between the scores in the acetylleucine and placebo groups. Post-rotatory nystagmus peak velocity and time constant also declined in both groups at the same rate. Thus, acetylleucine neither reduced the nausea associated with this provocative stimulus, nor hastened the acquisition or retention of vestibular habituation of motion sickness and nystagmus. There was no difference in optokinetic nystagmus and smooth pursuit between the acetylleucine and placebo groups. However, subjects showed larger error in the subjective visual vertical after habituation, which indicates that spatial orientation is also affected by vestibular training.
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.”
When a man is accelerated on a centrifuge, the direction of gravitoinertial vertical changes relative to his body. However, a lag occurs in his perception of this change. The hypothesis has been advanced that the perceptual lag in this situation is partly the result of a conflict between signals arising from the semicircular canals and from the otolith organs. To test this hypothesis, subjects were tilted in such a way that they received consistent semicircular canal and otolith signals. This was accomplished simply by tilting them 30 deg from upright in their frontal plane. Immediately after being tilted, these subjects made estimates of the vertical which were approximately accurate, and they continued to make accurate estimates throughout a 140 sec judgment period. The absence of a perceptual lag under these circumstances supports the hypothesis.
The etiology of motion sickness is now usually explained in terms of a qualitatively formulated "sensory conflict" hypothesis. By consideration of the information processing task faced by the central nervous system in estimating body spatial orientation and in controlling active body movement using an "internal model" referenced control strategy, a mathematical model for sensory conflict generation is developed. The model incorporates and extends models proposed by von Holst, Held, and Reason, and is congruent with multisensory models for spatial orientation developed by Young and coworkers. The model postulates a major dynamic functional role for sensory conflict signals in movement control, as well as in sensory-motor adaptation. It accounts for the role of active movement in creating motion sickness symptoms in some experimental circumstances, and in alleviating them in others. The relationship between motion sickness produced by "sensory rearrangement" and that resulting from external motion disturbances is explicitly defined. A nonlinear conflict averaging model is proposed which describes dynamic aspects of experimentally observed subjective discomfort sensation, and suggests resulting behaviours. The model admits several possibilities for adaptive mechanisms which do not involve internal model updating. Further systematic efforts to experimentally refine and validate the model are indicated.
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.