There are a number of video games called “first-person shoot-em ups” and 3D environments – typified by the classic games DOOM and Black & White. The game engine creates a complex environment, or Virtual Reality, where first person perspective changes at the touch of a mouse or cursor. But these “first person perspective” games generate frequent dramatic perspective changes while the body remains stationary. In the game, the “player” can quickly whip the image through 180 degrees of scenery.
The result is a first-rate case of “car sickness” – the most common effects of simulator exposure resemble the symptoms of motion sickness: general discomfort, drowsiness, pallor, sweating, nausea, and, occasionally, vomiting.
To those of you out there, I can commiserate! For I too suffer from what the U.S. Army has classified as “simulator sickness”. If your friends have ever called you a WIMP for throwing-up or getting sick to your stomach after playing these games – it is NOT your fault.
Simulator sickness was explored by Eugenia M. Kolasinsk, Stephen L. Goldberg, and Jack H. Hiller, of the U.S. Army Research Institute for the Behavioral and Social Sciences, in Army Project Number 2O262785A791. They published their findings under “Technical Report 1027 – Simulator Sickness in Virtual Environments”, in May 1995. The entire report can be read via http://www.cyberedge.com/4a7b.html, and this article contains excerpts used by permission.
The exact cause or causes of simulator sickness is not known. However, a primary suspected cause is inconsistent information about body orientation and motion received by the different senses, known as the cue conflict theory. For example, the visual system may perceive that the body is moving rapidly, while the vestibular system perceives that the body is stationary. Inconsistent, non-natural information within a single sense has also been prominent among suggested causes.
Although Virtual Reality (VR) technology is very promising, there exists a potential threat to the ultimate usability of virtual environments: some users experience discomfort during, and sometimes after, a session in a simulated environment. Similar reactions have been observed in driving simulators and military flight simulators. This phenomenon is called simulator sickness and it is similar to motion sickness. There is a direct link between simulator sickness and sickness in virtual environments: both are forms of visually-induced motion sickness. Thus, the abundant simulator sickness literature, as well as the motion sickness literature, forms an excellent background and starting place in the study of sickness in virtual environments. Although most of the simulator sickness research involves military pilots and flight simulators, many of the findings may be directly applicable to VE systems. These findings can help identify potential factors involved in sickness, as well as suggest ways to combat it.
Video Gamers – The first important thing to recognize is that the longer you play, the more severe will be any potential consequences.
In the Army’s review of response data from 742 pilot exposures from 11 military simulators, they found that approximately half of the pilots (334) reported post-effects of some kind: 250 (34%) reported that symptoms dissipated in less than 1 hour, 44 (6%) reported that symptoms lasted longer than 4 hours, and 28 (4%) reported that symptoms lasted longer than 6 hours. There were also 4 (1%) reported cases of spontaneously occurring flashbacks. Since typical post-simulator duties and debriefing are not usually time-consuming, one hour is probably the longest period a pilot would ordinarily be expected to remain at the simulator site. Thus, longer-lasting aftereffects, especially those such as flashbacks and dizziness, pose a safety risk to both the pilots and to others.
Visual problems can also develop – One common effect of exposure to virtual environments is eye strain and related oculomotor problems. According to Stone (1993), two groups of British researchers found that only ten minutes spent wearing a HMD can result in side effects such as what might be observed after eight hours spent in front of a Cathode Ray Tube (CRT) display: headaches, nausea, and blurred vision, for example. Stone expressed concern over the strain imposed on binocular vision by HMDs. He pointed out that, whereas binocular vision is fully developed in adults, it is not fully developed in children under 12 and, thus, is more likely to break down under stress, causing squinting. It is Stone’s opinion that the visual and motor system effects, although mostly anecdotal, are potentially serious, especially for lower quality VE systems such as those geared for entertainment. As Stone indicated, problems such as binocular convergence, inappropriate accommodative response to blurred images, unequal focusing capability in each eye, and inadequate fixation or pursuit eye movements are all evident in current Liquid Crystal Display (LCD)-based HMDs. These problems are known to contribute to a disorder known as asthenopia, which Stone described as a type of oculomotor instability.
Display flicker (CRT refresh rate) reveals that flicker is something to be avoided if at all possible since it is distracting, induces eye fatigue, and appears to be associated with simulator sickness (e.g., Harwood & Foley, 1987; Pausch et al., 1992; Rinalducci & MacArthur). The perception of flicker differs among individuals and depends on an individual’s flicker fusion frequency threshold, as discussed in the previous section.
Several aspects of the visual display affect the perception of flicker. Of these aspects, those most applicable to the visual displays of virtual reality systems are refresh rate, luminance level, and field-of-view (e.g., Boff & Lincoln, 1988; Farrell, Casson, Haynie, & Benson, 1988; Maxwell, 1992). In order to suppress flicker, refresh rate must increase as the luminance level increases (Farrell et al.). Refresh rate must also increase as field-of-view increases, since a large field-of-view increases the likelihood that flicker will be perceived (Maxwell). This is due to the fact that the peripheral visual system is more sensitive to flicker than is the fovea (Boff & Lincoln, 1988). Thus, in selecting a visual display, several trade-offs are necessary. In order to suppress flicker, refresh rate must increase as both luminance level and field-of-view increase. However, displays with faster refresh rates cost more. Thus, slower refresh rates may be employed in an effort to keep costs down. Slower refresh rates, however, promote flicker and require more persistent phosphors. But long-persistence phosphors promote phosphor lag, which may lead to disturbing smeared images (Pausch et al., 1992).
There really is no summary to this article. It is meant to identify to avid Video Gamers that simulator sickness is real and is not something to be taken lightly. If you suffer from it, enjoy other games which do not involve rapidly changing perspectives. If you do not, be aware of the susceptibility for symptoms the longer you play – if you start feeling disoriented, stop. Obviously, there is the important overall consideration – if you feel sick – GO TO THE DOCTOR! We aren’t diagnosing anyone here, only informing you of what military pilots and the US Army discovered about simulator sickness… so use this information accordingly.