The following research questions were posed at the top of Chapter 6:
Experiments AIIIE1 and AIIIE2 answered all of these questions in the affirmative. However, these experiments dealt only with a ``low-end'' system based on the Virtual i-O i-glasses!. An important open problem is to investigate the usefulness of the IVB technique for high-end systems.
Pilot Study AIIIP2 (see Appendix D) was a very brief investigation of a simple background grid as an IVB for a high-end driving simulator. It failed to find a reduction in simulator sickness. Pilot Study AIIIP2 is reported because it serendipitiously found a possible nulling presence measure suitable for interactive environments. The possible measure will be discussed in Chapter 8. The below comments on the underlying phenomenon.
Pilot Study AIIIP2 used a simple background grid for the IVB, displayed in the sky portion of the simulator scene. The grid was kept fixed with respect to the laboratory at all times. There was a fascinating effect in which the background grid appeared to rotate in the opposite direction when the CI turned, even though the background grid was stationary with respect to the laboratory. This is known as ``induced motion'': the apparent motion of a stimulus caused by motion of nearby stimuli (see Section 3.3.2).
While it is usually a motion of the visual background which produces an induced motion of a foreground object, the reverse is not unknown. Levine and Shefner  give the following example: ``...consider a cloudy night sky with the moon ducking in and out of the drifting clouds. The moon is actually stationary relative to the clouds, but because the clouds take up so much more room in the visual field than the moon, they appear to be stationary while the moon seems to move in the opposite direction from them.'' (p. 382.)
See Section 3.3.1 for a discussion of why this induced motion may have occurred. It seems likely that a more compelling visual background than a simple grid would serve to reduce simulator sickness. But this remains a topic for future research.