Four possible short-comings were identified with Experiment AIIIE1.
First, the visual background might have been simply ``washing out'' the vection stimulus in the CI. This seems unlikely, given that participants rated the IVB as less visible than the CI (mean rating of 2, with 1 indicating only the CI was visible, 5 indicating only the IVB was visible).
Second, performance of the head rolls by the participant often varied within and between sessions, as well as between participants.
Third, the time between sessions may not have been long enough to prevent carryover effects.
Fourth, it was possible that subjects were simply ignoring the CI in the see-through condition. An IVB is only useful if it confers value while the subject is primarily attending to the CI, where the simulator task is being performed.
Experiment AIIIE2 was similar to Experiment AIIIE1, with a few refinements described in the Methods section. The refinements were intended to address the above issues. Most importantly, a visual task was provided to direct attention into the visual foreground. This controlled for the degree to which participants attended to the visual foreground. It also created a stronger link to a real simulator task, in which attention would have to be focused on the visual foreground, rather than the IVB.
As with Experiment AIIIE1, it was hypothesized that the IVB condition would produce less simulator side-effects than the non-IVB condition.