Jelte E. Bos

Theoretical considerations on canal-otolith interaction and an observer model.

Abstract. Subjective vertical orientation, eye and body movements, and motion sickness all depend on the way our central nervous system deals with the gravito-inertial force resolution problem: how to discern accelerations due to motion from those due to gravity, despite these accelerations being physically indistinguishable. To control body or eye movements, the accelerations due to motion should be known explicitly. Hence, somehow gravity should be filtered out of the specific force or gravito-inertial acceleration (GIA, the sum of both accelerations) as sensed by the otoliths, which are the linear accelerometers in the inner ear. As the GIA also changes in a head-fixed frame of reference when the head is rotated, angular motion as sensed by the semicircular canals in the inner ear should also be considered. We present here a theoretical approach to this problem, and show that the mathematical description of canal–otolith interaction is in fact a three-dimensional equivalent of the two-dimensional description given by Mayne in 1974. A simple low-pass filter is used to divide the GIA into a motion and a gravity component. The retardation of the somatogravic effect by concomitant angular motion during centrifugation is shown as a result. Furthermore we show how the canal–otolith interaction fits within the framework of an observer model to describe subjective vertical orientation, eye movement and motion sickness characteristics. To predict a frequency peak in sickness severity, for example, it is necessary to explicitly include the Mayne equation operating both on sensor afferents and in the internal model. From tilt and translation data from centrifugation and horizontal oscillation, as well as from motion sickness data, we conclude that the time constant of the low-pass filter is in the order of seconds instead of tens of seconds as assumed before. Several corollaries are additionally discussed as a result.

A theory on visually induced motion sickness

Op basis van kennis over het evenwicht, Einsteins gelijkheidsprincipe, neurofysiologie en regeltechniek wordt een raamwerk geboden voor het begrijpen, voorspellen en nader onderzoeken van het verschijnsel dat we misselijk kunnen worden van het kijken naar bewegende beelden.

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 tactile cockpit instrument supports the control of self-motion during spatial disorientation

Objective: We investigated the effectiveness of a tactile torso display as a counter-measure to spatial disorientation (SD) and compared inside-out and outside-in codings. Background: SD is a serious threat to military as well as civilian pilots and aircraft. Considerable effort has been put into SD countermeasures such as training programs and advanced cockpit displays. Tactile displays have been considered a promising technology. Method: Twenty-four participants were assigned to the two coding groups (12 per group and matched for age and gender). We used a rotating chair to build up a state of SD by rotating participants around their yaw axis followed by a sudden stop. During the following recovery phase a random disturbance signal was added to the chairs orientation. Participants actively controlled their orientation and were instructed to maintain a stable orientation. Results: Statistical analyses revealed that recovery from SD was improved with support of the tactile instrument, but tracking performance was reduced. The effects were the same whether the instrument was available full time or during the recovery phase only. There were no differences between outside-in and inside-out coding. Conclusion: The present study demonstrates the potential of tactile cockpit instruments in controlling SD, even in the presence of strong but misleading self-motion information from the vestibular sense. Application: Actual or potential applications of this research include spatial disorientation countermeasures for pilots, divers, and astronauts.

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.

Saccular impact on ocular torsion

When someone is tilted laterally, the shear force on the maculae of the utriculus and the sacculus is described by the sine and the cosine of the angle of tilt, respectively. So both the sacculus and the utriculus are stimulated, but in the literature, ocular torsion is normally attributed to utricular function alone (and, thus, seen as a response to y-axis linear acceleration). However, on the base of a series of experiments on a tilt chair, a linear track, human centrifuges, and during parabolic flights, we conclude that the sacculus contributes to ocular torsion as well (there is a response to z-axis linear acceleration). The data suggest that the ratio of the utricular and saccular impact on ocular torsion is 3:1. The utriculus generates conjugate and the sacculus disjunctive torsional eye movements.

Self-driving carsickness

This paper discusses the predicted increase in the occurrence and severity of motion sickness in self-driving cars. Self-driving cars have the potential to lead to significant benefits. From the drivers perspective, the direct benefits of this technology are considered increased comfort and productivity. However, we here show that the envisaged scenarios all lead to an increased risk of motion sickness. As such, the benefits this technology is assumed to bring may not be capitalised on, in particular by those already susceptible to motion sickness. This can negatively affect user acceptance and uptake and, in turn, limit the potential socioeconomic benefits that this emerging technology may provide. Following a discussion on the causes of motion sickness in the context of self-driving cars, we present guidelines to steer the design and development of automated vehicle technologies. The aim is to limit or avoid the impact of motion sickness and ultimately promote the uptake of self-driving cars. Attention is also given to less well known consequences of motion sickness, in particular negative aftereffects such as postural instability, and detrimental effects on task performance and how this may impact the use and design of self-driving cars. We conclude that basic perceptual mechanisms need to be considered in the design process whereby self-driving cars cannot simply be thought of as living rooms, offices, or entertainment venues on wheels.

The effect of internal and external fields of view on visually induced motion sickness.

Field of view (FOV) is said to affect visually induced motion sickness. FOV, however, is characterized by an internal setting used by the graphics generator (iFOV) and an external factor determined by screen size and viewing distance (eFOV). We hypothesized that especially the incongruence between iFOV and eFOV would lead to sickness. To that end we used a computer game environment with different iFOV and eFOV settings, and found the opposite effect. We speculate that the relative large differences between iFOV and eFOV used in this experiment caused the discrepancy, as may be explained by assuming an observer model controlling body motion.

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.

Simulator sickness depends on frequency of the simulator motion mismatch: An observation

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 simulatorthat were performed for other reasons than the purpose of this studywe 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.