Virtual Reality Scientific and Technological Challenges (1995) / Chapter Skim
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6 Whole-Body Motion, Motion Sickness, and Locomotion Interfaces
6 Whole-Body Motion, Motion Sickness, and Locomotion Interfaces
Pages 205-230
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From page 205... ...
In the case of passive transport in a vehicle, haptic interfaces with the vehicle are the places at which the vehicle applies accelerative forces to the individual's body. The haptic stimulation associated with these forces contributes to the perception of body motion.
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From page 206... ...
All of these issues are critical to understanding how people will adapt to VEs involving locomotory movements, passive transport, and head, arm, and torso movements. However, it is important to recognize that our knowledge of these areas is incomplete.
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From page 207... ...
, as well as for other types of situations (e.g., Welch et al., 1993~. Head Movements Head movements made during exposure to increased or decreased gravitoinertial force background levels tend to bring on symptoms of motion sickness because the normal patterning of sensorimotor control of the head and patterns of sensory feedback are disrupted (Lackner and Graybiel, 1984a, 1985, 1987; Lackner et al., 1991~.
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From page 208... ...
Accordingly, VE displays that induce apparent whole-body motion and that require head movements are likely to elicit greater levels of sickness the greater the fidelity of the experienced self-motion and sense of presence. Altering the sensorimotor control of the head with a neck brace can be mildly provocative.
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From page 209... ...
For example, the driver of a vehicle will physically lean into a turn (Fukuda, 1975~. Arm movements made during exposure to passive rotation of the body generate Coriolis forces that deviate the arm from its intended trajectory and target.
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From page 210... ...
These findings are relevant to movement control in VEs for several reasons. First, in everyday behavior, reaching movements made during voluntary body movements of the trunk or whole body generate Coriolis forces far in excess of those used in experimental studies, yet movements are made accurately.
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From page 211... ...
These remappings are such as to normalize the experienced body displacement through space and the apparent frequency, direction, and length of stepping movements (Lackner and DiZio, 1988, 1992, 19931. If visual flow is double normal for the stepping movements being made, the individual will perceive either an increase in stepping rate or that the stepping leg lengthens to give the extra displacement to the body.
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From page 212... ...
Height vertigo-sensations of fright and instability usually accompanied by increased body sway occur when the viewing perspective is elevated and there are no nearby objects visible (Bles et al., 1980~. NIE systems will have the clear potential to create such circum
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From page 213... ...
When the illusion of self-motion (vection) is highly compelling, tilting head movements can elicit disorientation (pseudo-Coriolis effects partly analogous to those that occur when head movements are made during actual body rotation)
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From page 214... ...
Rotating sound fields that have strong spatial volume distribution can elicit apparent motion as well as eye movements compensatory for the apparent motion in subjects in the dark (Lackner, 1977~. Head movements strongly suppress the induction of apparent self-motion by sound fields.
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From page 215... ...
Intersensory effects provide ways of creating various patterns of compelling apparent self-motion and changes in apparent body orientation in stationary individuals. Such experienced motion is usually accompanied by compensatory eye movements and other compensatory postural changes.
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From page 216... ...
216 au ._ o o N ._, 50 o U .
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From page 217... ...
Motion sickness is often attributed to sensory conflict because many situations that evoke sickness are associated with various types of conflicts between different receptor system activities, for example, visual versus semicircular canal signals. Conflict theories generally involve neural models of the environment or of the physiological control systems of the body; so, for example, conflict occurs when expectation based on previous experience does not match current inputs during voluntary body movements (Reason and Brand, 1975~.
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From page 218... ...
A confounding factor in predicting susceptibility to motion sickness is that an individual's susceptibility to one form of provocative motion may not correlate well with susceptibility to another form (Miller arid Graybiel, 1972; Calkins et al., 19871. For example, susceptibility in situations primarily involving canal stimulation may not correlate well with those primarily involving otolith stimulation, such as bithermal caloric irrigation (to activate horizontal semicircular canals)
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From page 219... ...
For example, adaptation to rotating environments can be achieved by initially exposing individuals to a very low rate of rotation, one that neither disrupts motor control nor elicits motion sickness, and having them make many head and body movements (Graybiel et al., 1968; Graybiel and Knepton, 1976~. By repeating the movements after additional 1 rpm increases in velocity, it is possible to adapt individuals to quite high velocities of rotation without significant performance decrements and without eliciting motion sickness.
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From page 220... ...
In the following discussion, we consider a variety of interface systems or system components relevant to whole-body motion for teleoperator and VE systems. The discussion is subdivided into three subsections: inertial displays, locomotion displays, and noninertial displays.
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From page 221... ...
All the systems in this class can reproduce the specified patterns of force vectors imposed on an individual or other object that remains stationary within the simulator. However, all of them fail to simulate both the mechanical dynamics of any voluntary movements made within the simulator and the vestibular stimulation that would be generated during head movements.
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From page 222... ...
This rotating room is an extremely flexible research tool that enables a subject to be exposed to a noninertial, non-lG force background while moving about freely and being monitored by complex on-board equipment. Examples of the room's flexibility as a research tool is the ability it gives to investigate all of the fundamental problems described in the first section of this chapter, including the nature of automatic load compensation during arm and head movements, the control of eye movements, and sensory localization during body movement.
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From page 223... ...
The motor and belt have a combined stiffness that allows the horizontal ground contact forces usually applied in walking to be manipulated. It is microprocessor-controlled so that users can preprogram their preferred exercise regimens, but real-time control must be achieved by a custom interface.
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From page 224... ...
Noninertial Displays Noninertial displays induce a sense of whole-body movement in stationary individuals although they can also be used in conjunction with moving bases. Many simulators currently work by presenting stationary individuals with stimuli that are normally associated with body motion so as to enhance a sense of self-motion.
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From page 225... ...
fields of view, the preference for high resolution, and changes in the visual scene to accommodate head movements will generate a high demand for computational and rendering speeds. Although there is no clear psychophysical data on required frame rates, occasional skips in a display that is being generated at an average rate of 30 frames per second can reduce the sense of virtual body motion (assuming there is no moving base or any other supplementary stimulus)
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From page 226... ...
Vestibular Displays A sense of body motion in a stationary subject can also be elicited artificially by stimulating the semicircular canals of the vestibular system. One method consists of directing streams of cool air or water into one auditory canal and warm into the other.
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From page 227... ...
The movements experienced can be supranormal in the sense that anatomically impossible apparent body configurations are generated for example, hyperextension of limbs. J ~-DO ' ~ RESEARCH NEEDS The research and development efforts on whole-body motion displays that are needed for development of the SE field, beyond those di
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From page 228... ...
The lack of expected feedback for the state of body motion being experienced can inhibit the perception of self-motion and lead to a perceptual mapping that better fits all the current sensors. Making head movements during visually induced illusory self-motion can suppress or enhance the sense of self-motion, depending on whether those movements are in the plane of motion and begin when visual stimulation begins or are out of the motion plane and begin after its onset.
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From page 229... ...
· Visual displays Requirements on visual displays imposed by consideration of passive whole-body motion or active locomotion are similar to those previously mentioned in other chapters: the best displays would be an HMD that is inexpensive, lightweight, and comfortable; has high resolution and a wide field of view (both horizontally and vertically) ; and includes both full-color images and refined stereopsis.
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From page 230... ...
· Sensorimotor loops Many SE systems introduce distortions, time delays, gain changes, and statistical variability (noise) between voluntary movements and associated patterns of sensory feedback.
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