forum Spotlight On: Simulator Sickness Spatial Orientation, Adaptation, and Motion Sickness in Real and Virtual Environments Reason and Brand (1975) traced the first written report diopulmonary function, phasic skin conductance, and of sea sickness to Hippocrates, 2400 years ago. They also peripheral blood flow) has proven helpful for under- noted that motion sickness occurs in many situations standing the physiology of motion sickness under labo- involving either passive body motion or active interac- ratory conditions but is insensitive, nonspecific, unreli- tion with the world via indirect sensorimotor interfaces able, and/or restrictive under operational conditions (e.g., prism spectacles). The best advice for avoiding (Cowings, Suter, Toscano, Kamiya, 8c Naifeh, 1986; motion sickness in such situations (without medication) Golding, 1992; Graybiel 8c Lackner, 1980; Lawson 8c is to refrain from moving your head, to keep your eyes Lackner, 1992; Stern, Koch, Leibowitz, Linblad, Shu- closed, and to move as economically as possible. This pert, 8c Stewart, 1985; Sunahara, Johnson, 8c Taylor, must sound hopelessly restrictive to anyone contemplat- 1964). In flight simulators (Kennedy, Lilienthal, Ber- ing virtual environment ( VE) systems in which users baum, Baltzley, 8c McCauley, 1989) and in our psycho- may play an active part, computers and specialized dis- physical experiments that involve real or apparent body plays are the user's interface to the world, and the experi- motion (e.g., Lackner 8c Texiera, 1977), it is uncom- enced world may purposely not correspond to the actual mon to observe severe symptoms—extreme nausea or world. As might be expected motion sickness is being vomiting, the skin appearing white as a sheet, and the reported in VEs that involve apparent self-motion clothes being soaked with perspiration. But close obser- through space, the best known examples being flight vation may reveal that the subject's upper lip or palms simulators (Kennedy, Hettinger, 8c Lilienthal, 1990). are damp, swallowing is frequent (stomach discomfort The goals of this paper are to introduce motion sickness and increased salivation), and he or she is unresponsive symptomatology, to outline some concepts that are cen- (eye strain, drowsiness, lack of initiative) and complains tral to theories of motion sickness, spatial orientation, of headache and fatigue. Drowsiness or a feeling of and adaptation, and to discuss the implications of some "spaciness" is sometimes the sole symptom and can dis- trends in VE research and development. rupt the remainder of a day's work. This has been dubbed "The Sopite Syndrome" by Graybiel and Knep- ton (1976). Eye strain, headache, and dizziness and fa- I Motion Sickness Symptomatology tigue are the most likely symptoms to be associated with viewing a wide-field visual display depicting body mo- The signs and symptoms of motion sickness in- tion through the environment (Kennedy et al., 1989, clude nausea and vomiting, cold sweating, pallor, saliva- 1990; Lackner 8c Texiera, 1977); nausea, salivation, pal- tion, drowsiness, dizziness, headache, eye strain, leth- lor, and sweating usually follow a period of unusual, argy, lack of initiative, and chronic fatigue. These indices prolonged, or intense linear and angular acceleration, appear with various severities and in different combina- especially if head movements are made (Johnson, tions depending on the exposure conditions and the in- Stubbs, Kelks, 8c Franks, 1951). The former set of dividual. Almost all systems for rating symptoms and symptoms will likely prevail in VEs, which will probably calculating motion sickness severity rely on subjective exclude intense accelerations. observation and self-report (e.g., Graybiel, Wood, Miller, 8c Cramer, 1968). Monitoring physiological cor- relates of motion sickness (e.g., electrogastrograms, car- Paul DiZio and James R. Lackner Ashton Graybiel Spatial Orientation Laboratory Presence, Volume I, Number3. Summer 1992 Brandeis University © / 992 The Massachusetts Institute of Technolog/ Waltham, Massachusetts 02254-91 10 DiZio and Lackner 319 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/pres.1992.1.3.319 by guest on 02 October 2021 320 PRESENCE: VOLUME I, NUMBER 3 These signs and symptoms can appear within minutes head, optical flow is upward relative to the head, which of acute exposure to a nauseogenic environment or take is opposite to what would normally occur for the actual hours, and they can disappear within minutes after expo- inertial motion; the correlations among visual, auditory, sure ends or persist for hours. Symptoms usually abate if and proprioceptive information from an object that can exposure to the stimulus is prolonged but often re- be seen, heard, and touched are systematically altered; emerge upon return to normal conditions (Graybiel, the eyes and head will assume new tonic postures relative Kennedy, Knoblock, Guedry, Mertz, McLeod, Cole- to the head and torso, respectively, because of changes in hour, Miller, 8c Fregly, 1965). the visual horizon, altering their habitual relationship to the gravitoinertial field. Sensory conflict theories do not predict which of these 2 Motion Sickness and Sensorimotor sensorimotor rearrangements will generate conflict sig- Rearrangements nals and which will not, nor do they help quantify the magnitude of conflict. They do not even help in develop- There are few principles that predict whether a ing a comprehensive list of potentially relevant sensori- situation will bring about motion sickness or what par- motor rearrangements because this depends on under- ticular signs and symptoms will be involved. Sensory standing spatial orientation at many levels of analysis. conflict models have been proposed to explain some of Conflict theories actually restate the obvious, that senso- the facts concerning the relationship between control of rimotor rearrangement is correlated with self-limiting orientation and motion sickness. In general, they assume motion sickness and degradation of orientation control, that the central nervous system is able to generate expec- and beg the important questions of identifying normal tations of the patterns of vestibular and other sensory versus abnormal sensorimotor relationships. feedback appropriate for intended voluntary body move- Sensory conflict theories embody the notion that spe- ments. Sometimes a "neural model" of the current physi- cific movements are associated with single, fixed relation- cal environment (Reason 8c Brand, 1975) or of the ships between sensory and motor signals. Several investi- physiological control system itself (Oman, 1982) is ex- gators have criticized this approach with regard to plicitly proposed for producing such an expectation. If theories of movement control in general (Bernstein, sensory feedback associated with voluntary movement 1967; Lackner, 1981). Multiple levels of analysis are does not match expectation because of transport in a necessary for investigating spatial orientation, adapta- vehicle or because a sensorimotor rearrangement (e.g., tion, and motion sickness. These include describing or- reversing prism spectacles) has been introduced, a con- ganism-environment interactions in optical, mechanical, flict signal is generated that ultimately produces symp- and acoustical terms (cf. Gibson, 1966) and understand- toms. For example, moving the head while wearing ing specific sensor)' and effector systems as well as spe- prism spectacles that reverse or invert objects in the vi- cialized sensorimotor subsystems such as the vestibulo- sual field elicits motion sickness symptoms and visual ocular reflex. Abstract representations of terrestrial illusions and impairs control of voluntary movement; conditions that constrain perceptual mappings of affer- moreover, during continued exposure, the motion sick- ent and efferent signals are also essential. Real environ- ness abates at about the same rate that perceptual and ments and VEs may be nauseogenic because of sensori- motor errors diminish (Gonshor 8c Melvill Jones, 1976; motor rearrangements that are disruptive to one or more Stratton, 1897). of these layers of orientation control, and individuals Inverting prisms lead to the following rearrangements may differ in the operation of the layers and thus in sus- in the relationship between movement and sensorimotor ceptibility to different "environments." feedback: one must raise one's head to direct gaze to- An organism's spatial orientation systems are cali- ward an object seen as down; during elevation of the brated in the sense that they transform patterned sensory Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/pres.1992.1.3.319 by guest on 02 October 2021 DiZio and Lackner 321 and motor signals into dynamic information about the 3 Motion Sickness and Sensorimotor environment and the self in dimensions and units appro- Rearrangements in VEs priate for accurate perception and coordinated action. That is, spatial orientation systems instantiate transfor- Long-standing observations indicate that sensori- mational computations and solve for the parameters ap- motor rearrangements that disrupt control of head propriate for the current gravitoinertial force, optical, movements are potent etiological factors in motion sick- and acoustic background. This can be simplified for the ness (James, 1882; Johnson et al., 1951; Purkinje, nervous system by the imposition of geometric and dy- 1820). Despite the limited and inchoate theories of spa- namic