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This week's episode is a first experiment with a heavy content - instead of free discussion based on recent news, we do a detailed research on a certain key topic for virtual reality - listeners get practical tips based on theories and studies, with examples and references.
This week we talk about motion sickness. Starting from bigger picture - Adverse health problems in VR, getting a quick glance at symptoms and continuing towards theory and practice.
If you missed something during podcast or want to get a reference or link, check further show notes - all and more is there.
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1. Adverse health problems of VR
- Motion sickness
- eye strain
- fatigue (e.x. gorilla arm)
- physical injuries (e.x. muscle straining from repeated movement)
2. Motion Sickness symptoms
- eyestrain, difficulty focusing, blurred vision, and headache
- dizziness, vertigo
- stomach awareness, increased salivation, and burping
- motion sickness - adverse symptoms and readily observable signs that are associated with exposure to real (physical or visual) and/or apparent motion (Lawson, 2014)
- cybersickness - visually induced motion sickness resulting from immersion in a computer-generated virtual world simulator sickness - results from shortcomings of the simulation, but not from the actual situation that is being simulated (Pausch et al., 1992)
- VR sickness - all of the above combined - separatelly do not cover all there is do motion sickness in VR;
motion sickness may result when the environment is altered in such a way that incoming information across sensory modalities (primarily visual and vestibular) are not compatible with each other and do not match our mental model of expectations (Reason and Brand 1975)
evolutionary / poison
If we get conflicting information from our senses, it means something is not right with our perceptual and motor systems. Our bodies have evolved to protect us by minimizing physiological disturbances produced by absorbed toxins
postural instability theory
predicts that sickness results when an animal lacks or has not yet learned strategies for maintaining postural stability (Riccio and Stoffregen 1991) They suggest people need to learn new patterns in novel situations to control their postural stability. Until this learning is completed, sickness may result.
rest frame hypothesis
motion sickness does not arise from conflicting orientation and motion cues directly, but rather from conflicting stationary frames of reference implied by those cues (Prothero and Parker 2003)
eye movement theory
motion sickness occurs due to the unnatural eye motion required to keep the scene’s image stable on the retina. If the image moves differently than expected, such as often occurs in VR, then a conflict occurs between what the eyes expect and what actually occurs. The eyes then must move differently than they do in the real world in order to stabilize the image on the retina. As a result of this discrepancy, motion sickness results
5. Measuring motion sickness
- large variance between individuals
- adaptation of the same user
- large sample size required
Subjective: The Kennedy Simulator Sickness Questionnaire
- 4 point scale: “none,” “slight,” “moderate,” or “severe.”
- 4 scores: total + partial for each cluster
- give only after exposure to decrease expectations bias
- 2180 users of 16 US Navy flight simulators
(Kennedy and Fowlkes 1993)
Behavioral: postural stability
The number of times a subject breaks the stance is the postural instability measure. * type 1: static postural stability Sharpened Romberg Stance: one foot in front of the other with heel touching toe, weight evenly distributed between the legs, arms folded across the chest, chin up. The number of times a subject breaks the stance is the postural instability measure * type 2: dynamic postural stability: assess body sway with body tracking, e.x. with Kinect
6. Factors contributing to motion sickness
System / technology factors
- latency (<30ms)
- calibration: accurate tracker offsets (the world-to-tracker offset, tracker-to-sensor offset, sensor-to-display offset, display-to-eye offset), mismatched field-of-view parameters, misalignment of optics, incorrect distortion parameters, etc.
- tracking accuracy
- tracking precision
- lack of position tracking
- FOV: Displays with wide field of view result in more motion sickness due to (1) users being more sensitive to vection in the periphery, (2) the scene moving over a larger portion of the eyes, and (3) scene motion (either unintentional due to other shortcomings or intentional by design—e.g., when navigating through a world)
- refresh rate - high display refresh rates can reduce latency, judder, and flicker.
- judder - appearance of jerky or unsmooth visual motion
- display response time and persistence -if not optimal then can cause judder, motion smear/blur, flicker, and increased latency
- lateral movement
- experience with VR
- thinking about sickness
- females x3 > males
- expectations and mental model
- instruction as to how to put on HMD correctly
- sense of balance
- RW experience with task (the less the better)
Tricks & Examples
- prolonged use ⇒ adaptation, optimally sessions 2-5 days appart
- rest frames If some visual cues can be presented that are consistent with the vestibular system (even if other visual cues are not), motion sickness can be reduced
- 3D “HUD” - e.g. arrows (e.g.?)
- [virtual nose] (http://www.wired.com/2015/04/reduce-vr-sickness-just-add-virtual-nose/)
- grid technique
- manipulate the world as an object
- self motion
- world motion - isometric camera, lock position of camera, but move the whole world around it
- waypoints for fly-through experiences (leading indicators) - provide cues to predict movement
- motion platforms
- adventage: reduce vestibular-visual conflict
- causing incongruency between the physical motion and visual motion (the primary cause), and
- increasing physically induced motion sickness independent of how visuals move (a lesser cause)
- passive motion platforms Birdly by Somniacs is a flying simulation where the user becomes a bird flying above San Francisco. The user controls the tilt of the platform by leaning. The active control of flying with the arms also helps to reduce motion sickness. Motion sickness is further reduced because the user is lying down, so less postural instability occurs than if the user were standing.
- warning grids and fade-outs - in case more than just head rotation is used, there has to be a save valve for the moment when user leaves tracking range, for if the devices looses range, tracking will start randomly move around and will cause huge jutter among other things
Lawson, B. D. (2014). Motion Sickness Symptomatology and Origins. In K. Hale and K. Stanney (Eds.), Handbook of Virtual Environments (2nd ed., pp. 531–600). Boca Raton, FL: CRC Press. Pausch, R., Crea, T., and Conway, M. J. (1992). A Literature Survey for Virtual Environments: Military Flight Simulator Visual Systems and Simulator Sickness. PRESENCE: Teleoperators and Virtual Environments, 1(3), 344–363. 205 Reason, J. T., and Brand, J. J. (1975). Motion Sickness. London: Academic Press. Riccio, G. E., and Stoffregen, T. A. (1991). An Ecological Theory of Motion Sickness and Postural Instability. Ecological Psychology. DOI: 10.1207/s15326969eco0303_2 Prothero, J. D., and Parker, D. E. (2003). A Unified Approach to Presence and Motion Sickness. In L. J. Hettinger and M. Haas (Eds.), Virtual and Adaptive Environments (pp. 47–66). Boca Raton, FL: CRC Press. DOI: 10.1201/9781410608888.ch3 Kennedy, R. S., Lane, N. E., Berbaum, K. S., and Lilienthal, M. G. (1993). A Simulator Sickness Questionnaire (SSQ): A New Method for Quantifying Simulator Sickness. International Journal of Aviation Psychology, 3(3), 203–220 Jerald, J. (2016). The VR Book: Human-Centered Design for Virtual Reality
Huge credit goes to Jason Jared, the author of The VR Book, which was the starting point and main source of informaiton an show notes for this episode. For anyone interested in digging deeper than reality faster than our podcasts are released, we recommend full hearted this book.
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