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AR / VR Science Note 005: Causes and Susceptibility to Visually-Induced Motion Sickness

by Steve Aukstakalnis

Some of the most common complaints from users of fully immersive virtual reality systems are dizziness and nausea. This phenomenon is referred to by several names, including simulator sickness, cyber sickness, ‘RGB yawn,’ and visually induced motion sickness (VIMS). The full range of symptoms regularly reported includes nausea, increased salivation, drowsiness, disorientation, dizziness, headaches, difficulty focusing, blurred vision, and occasionally even vomiting. The onset of these symptoms can take place within minutes and may continue for some time after an immersive experience has concluded (Biocca, 1992; Ebenholtz, 1992; Pausch et al., 1992; Cobb et al., 1999).

Although standard motion sickness and VIMS share some similar symptoms, it is important to highlight the fact that standard motion sickness occurs in the absence of vection, which is the illusory visual sensation of self-motion in the absence of physical movement (Fischer and Kornmüller, 1930; Dichgans and Brandt, 1973).

VIMS is believed to result from a combination of physiological and technical factors, several of which are detailed below.

Physiological Factors in VIMS

The current, most widely held theory for these physiological responses and one that has withstood more than 40 years of debate is based on the idea of sensory conflict. First proposed in 1975 in relation to flight simulators (Reason and Brand, 1975), the theory holds that these physiological side effects are a result of the compelling visual sensation of motion without the corresponding vestibular or proprioceptive cues (Stanney and Kennedy, 2009; Groen and Bos 2008; Nichols and Patel, 2002; Reason and Brand, 1975).

For clarity, the visual system provides information relating to body orientation with respect to the visual world; the vestibular system offers information relating to linear and angular acceleration and position with respect to gravity; and the kinesthetic or proprioceptive system provides information relating to limb and body position (Barratt and Pool, 2008). In normal, day to day circumstances, this diverse array of sensory data is tightly aligned, providing various centers of the brain with key information about physical orientation, the environment, forces acting on the body, etc… Research suggests that it is a breakdown in this tightly coupled information flow, or conflicting sensory information, that results in the manifestation of VIMS symptoms.

Motion Sickness

Compelling vestibular and kinesthetic sensation of motion, but without corresponding visual cues (e.g.  in the belly of a boat during a storm)

Visually Induced Motion Sickness

Compelling visual sensation of motion but without the corresponding vestibular or kinesthetic cues (e.g. some VR sims, static flight simulators and other wide FOV displays.)

Additional theories have been proposed over the years as an explanation for VIMS. One such theory, known as the Ecological Theory, holds that these side effects result from prolonged instability in the control of posture (Riccio and Stoffregen, 1991; Bonnet et al., 2008). Readers should be firmly aware that the scientific community in no way has a full understanding of this topic (thus the use of the word theory). Additional research is ongoing.

Key Technology Factors in VIMS

Latency

A key performance and usability measure for all immersive virtual and augmented reality systems is that of latency, or the time lag between a user’s action and the system’s response to this action (Papadakis et al., 2011). Latency is a product of the processing, transport, and synchronization delays of key system components. It is well known to be detrimental to a primary factor that detracts from the sense of presence, a user’s sense of immersion, physical performance, and comfort level (Meehan et al., 2003; Friston and Steed, 2014). Perhaps most important to this chapter, latency can result in a breakdown between proprioceptive cues of the user and the visual stimuli shown in the display resulting in increased incidence of VIMS (Buker et al., 2012).

Persistence

This is the duration of time each pixel in a display remains lit. One of the effects of high persistence is the blurring and smearing of images which, in addition to contributing to poor image quality, has been associated with increased incidence of nausea and other forms of discomfort.

Incorrect Interpupillary Distance Settings

The distance between the centers of your pupils, known as the interpupillary distance (IPD), varies from person to person, by gender, and even by ethnicity. This measurement is extremely important for all binocular viewing systems ranging from standard eyewear to stereoscopic head-mounted displays.

When it comes to stereoscopic head-mounted displays, proper IPD settings are extremely important for a variety of reasons. Poor eye-lens alignment can result in image distortion, the effect of which can also result in eye strain and headaches and may contribute to the overall onset of VIMS (Ames et al., 2005). Incorrect settings can also impact ocular convergence and incorrect perception of the displayed imagery. For instance, when there is a greater-than-normal separation of inputs to the two eyes, the convergence angle to an object being viewed is increased, potentially resulting in the distance to a viewed object appearing shorter and the object appearing closer (Priot et al., 2006).

The mean adult IPD is around 63 mm, with the majority of adults having IPDs in the range 50–75 mm. Some fall into the wider range of 45–80 mm, however. The minimum IPD for children (down to five years old) is around 40 mm (Dodgson, 2004).

Display Field of View

As discussed in Chapter 3, “The Mechanics of Sight,” the combined field of view (FOV) of the human visual system measures approximately 200° horizontal by 130° vertical, with a centered binocular overlap of approximately 120° (Velger, 1998, p. 50). It is generally held that a wide FOV within a head-mounted display is better because it more closely simulates natural viewing and contributes to the user’s sense of immersion and presence within the simulation model (Primeau, 2000; Rogers et al., 2003).

Although this may be the case, it is important to point out that some studies suggest a wider FOV may also contribute to or increase the likelihood of VIMS. The basic premise is that a wide FOV display can induce a stronger perception of self-motion (vection) than a display with a restricted FOV (Pausch et al., 1992). Further, because flicker is most efficiently detected at the periphery of the visual field, consideration of refresh rates and luminance is also warranted (Kolasinski 1995).

Another potential contributing factor to the VIMS phenomenon is a discordance between the display field of view (DFOV) and geometric field of view (GFOV), which defines the horizontal and vertical boundaries of the perspective projection scene generated by a graphics engine (Draper et al., 2001).

Susceptibility to VIMS

Published research suggests that susceptibility to motion sickness in general and VIMS in particular is multifaceted, varying with age, ethnicity, gender, and overall health. For instance, the response is seen to be greatest between the ages of 2 and 12 (Stanney et al., 2002), slowing rapidly until about age 21 (Reason and Brand, 1975), and then increasing dramatically after age 50 (Brooks et al., 2010). People of Asiatic descent may be more susceptible than non-Asian counterparts (Barrett, 2004). Chinese women appear to be hyper sensitive to visually induced motion sickness (Stern et al., 1993). Women in general appear to be significantly more susceptible than men (Kennedy and Frank, 1985; Park et al., 2006; Kennedy et al., 1989).

Adaptation to VIMS

A fascinating aspect of the human perceptual system is the ability of many individuals to adapt to the sensory conflict with repeated exposure, not only to the specific stimuli leading to the condition but also with continued exposure to distorting lenses (Reason and Brand, 1975). Conversely, research also shows that adaptation to immersive virtual environments and a reduction in nausea results in an increase in after effects, including postural instability (Stanney and Salvendy 1998; Kennedy et al., 1997).

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This AR / VR Science Note is based on content drawn from the book Practical Augmented Reality: A Guide to the Technologies, Applications and Human Factors for AR and VR (Pearson / Addison Wesley Professional, Sept, 2016. Reproduced by the author with permission, Pearson © 2017).

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