Virtual Reality Sickness
Cyber sickness is the umbrella term for illness caused by using a computer display. Virtual reality sickness occurs when exposure to a virtual environment causes symptoms that are similar to motion sickness symptoms. The most common symptoms are general discomfort, headache, stomach awareness, nausea, vomiting, pallor, sweating, fatigue, drowsiness, disorientation, and apathy. Other symptoms include postural instability and retching. Virtual reality sickness is different from motion sickness in that it can be caused by the visually-induced perception of self-motion; real self-motion is not needed. It is also different from simulator sickness; non-virtual reality simulator sickness tends to be characterized by oculomotor disturbances, whereas virtual reality sickness tends to be characterized by disorientation.
Virtual reality sickness may have undesirable consequences beyond the sickness itself. For example, Crowley (1987) argued that flight simulator sickness could discourage pilots from using flight simulators, reduce the efficiency of training through distraction and the encouragement of adaptive behaviors that are unfavorable for performance, compromise ground safety or flight safety when sick and disoriented pilots leave the simulator. Similar consequences could be expected for virtual reality systems. Although the evidence for performance decrements due to virtual reality sickness is limited, research does suggest that virtual reality sickness is a major barrier to using virtual reality, indicating that virtual reality sickness may be a barrier to the effective use of training tools and rehabilitation tools in virtual reality. Estimates of the multi-study incidence and main symptoms of virtual reality sickness (also called cyber sickness) have been made.
There are various technical aspects of virtual reality that can induce sickness, such as mismatched motion, field of view, motion parallax, and viewing angle. Additionally, the amount of time spent in virtual reality can increase the presence of symptoms. Mismatched motion can be defined as a discrepancy between the motion of the simulation and the motion that the user expects. It is possible to induce motion sickness in virtual reality when the frequencies of mismatched motion are similar to those for motion sickness in reality, such as seasickness. These frequencies can be experimentally manipulated, but also have the propensity to arise from system errors. Generally, increasing the field of view increases incidence of simulator sickness symptoms. This relationship has been shown to be curvilinear, with symptoms approaching an asymptote for fields of view above 140°. Altering motion parallax distances to those less than the distance between the human eyes in large multiple-screen simulation setups can induce oculomotor distress, such as headaches, eyestrain, and blurred vision. There are fewer reports of oculomotor distress on smaller screens; however, most simulation setups with motion parallax effects can still induce eyestrain, fatigue, and general discomfort over time. Viewing angle has been shown to increase a user's sickness symptoms, especially at extreme angles. One example of such an extreme angle would be when a user must look downwards a short distance in front of their virtual feet. As opposed to a forward viewing angle, an extreme downward angle such as this has been shown to markedly increase sickness in virtual environments. Time spent immersed in a virtual environment contributes to sickness symptom presence due to the increasing effects of fatigue on the user. Oculomotor symptoms are the most common to occur due to immersion time, but the nature of the user's movements (e.g., whole-body vs. head-only) is suggested to be the primary cause of nausea or physical sickness.
Recent research has suggested that adults over the age of 50 are more susceptible than younger adults to virtual reality sickness. Women are more susceptible than men to virtual reality sickness this may be due to hormonal differences. Virtual reality sickness appears to increase in people who are not at their usual level of health, suggesting that virtual reality may not be appropriate for people who are fatigued, have not had enough sleep, are nauseated; or have an upper respiratory illness, ear trouble, or influenza, eyesight problem.