Visually induced motion sickness

The motion sickness examples so far have involved real motion. By contrast, motion sickness may occur by exposure to stimuli that convince the brain that accelerations are occurring, even though they are not. This is called apparent motion. The most commonly studied case is visually induced apparent motion, which is also called vection and was covered in Sections 8.4 and 10.2. Symptoms associated with this are part of visually induced motion sickness.

Vection (more generally, optical flow) can be generated in many ways. Recall from Figure 2.20 of Section 2.3 that extreme vection was caused by a room that swung while people remained fixed inside. Scientists use an optokinetic drum to conduct controlled experiments in vection and motion sickness by surrounding the subject with movable visual stimuli. Across a variety of studies that involve particular moving visual fields, only a few subjects are immune to side effects. About 50% to 100% experience dizziness and about 20% to 60% experience stomach symptoms; the exact level depends on the particular experiment [173].

Alternatively, displays may be used to generate vection. Recall from Section 6.2 that the optical flow perceived in this case is stroboscopic apparent motion due to a rapid succession of frames. The case of using displays is obviously of more interest to us; however, sickness studies that use optokinetic drums remain relevant because they serve as an important point of reference. They reveal how bad visually induced motion sickness can become, even in the limit of having no digital artifacts such as display resolution and frame rates.