In order to act effectively, people require information regarding how they are oriented and whether they are stationary or moving with respect their environment. Self-motion information--information regarding how one is moving with respect to environmental reference frames-is critical for successful goal-directed behavior. Distortion of self-orientation and self-motion information may lead to postural disturbance and motion sickness.
Motion, Simulator, and Virtual Environment Sickness
This paper addresses the disturbance and sickness frequently reported as a result of exposure to systems designed to simulate motion of the observer (Kennedy, Lane, Berbaum, & Lilienthal, 1993; Kennedy & Stanney, 1996). If one follows a motion cue conflict approach (Griffin, 1990; Reason, 1978; Reason & Brand, 1975), one may attribute motion sickness to a mismatch between visual cues indicating that the observer is stationary and inertial cues indicating that the observer is moving (e.g., when a person views an apparently stationary visual scene in a cabin below the deck of a boat moving on a stormy sea).
As noted later, receptors that detect inertial motion include the vestibular apparatus. Numerous studies indicate that motion sickness requires an intact vestibular system (Griffin, 1990). Consequently, this paper focuses on visual and vestibular system responses.
The phenomenon of simulator sickness (SS) is similar to motion sickness (Stanney & Salvendy, 1998). Symptoms for both include nausea, disorientation, oculomotor disturbances, and ataxia (Kennedy et al., 1993). SS is thought to be caused, in part, by the same motion cue conflicts that result in motion sickness. Of course, there are many different types of simulators and virtual environments (VEs) that could evoke sickness in different ways (Kennedy, Berbaum, & Lilienthal, 1997). Most simulators and VEs have the common feature that the visual scene is artificial, as opposed to a real visual environment. In many simulators and VEs, the self-motion and self-orientation cues received by the vestibular receptors differ from those received by the visual receptors, and this cue conflict may be the basic cause for the sickness. (For an alternative to the motion cue conflict approach, see the Appendix: Postural Instability Theory.)
Self-motion is detected by several receptors, including the vestibular apparatus, which is located in the inner ear. Vestibular receptors detect head/body movement (i.e., inertial motion). People can readily distinguish up from down and detect peaks of displacement when they are oscillated from side to side, even when they are in darkness (Guedry, 1974). Responses to vestibular stimulation include postural adjustments and perception of self-motion (Howard 1986a, 1986b; Parker, 1980, 1991).
Motion of a visual scene can be interpreted as motion of an object, such as a flying bird, with respect to the observer. Alternatively, visual scene motion can be perceived as self-motion: The visual scene may be perceived as stationary, and the self may be perceived as moving with respect to that scene (Berthoz, 2000). Visually induced perceived self-motion, which is sometimes labeled vection (Howard, 1986a), may evoke postural disturbances, as can be observed in large-screen theaters such as IMAX. Illusory self-motion evoked by visual scene motion is the basis for many aircraft and driving simulators as well as VEs and amusement park attractions (Rolfe & Staples, 1980).
Scene motion conditions that facilitate the self-motion interpretation have been addressed in numerous studies. Full-field scene motion readily leads to perceived self-motion. When the visual scene is divided into stationary and moving components, the part of the scene that is perceived as "background" may determine perceived self-motion direction as well as postural disturbances (Dichgans & Brandt, 1978: Howard, 1986a). …