The visual-inertial nulling measure found a main effect for treatment in the predicted direction of meaningful higher than random (p < .05). The reported presence measure showed a trend in the same direction (p <.10). Both measures showed reasonable test-retest reliability (.83 and .80, respectively).
It is not surprising that no relationship (.06 correlation) was found between the magnitude of the cross-over data and the magnitude of reported presence. This is consistent with the lack of a standard scale, between participants, governing how to assign numbers to mental states. However, there is a weak relationship (.38 correlation) between differences across treatment conditions across the two measures. Thus, participants who reported a large difference in presence between the two conditions showed a weak tendency to exhibit a corresponding large difference in the nulling measure.
While the current sample size did not show statistical significance, the correlation of the visual-inertial nulling measure with the EFT scores appears to be higher than the correlation of the reported presence measure with the EFT scores. This is consistent with the suggestion that the visual-inertial nulling measure is more closely related to field dependency, a factor which would be expected to influence between-subject variation in presence levels. This implies that the between-subject variation in the visual-inertial nulling measure may be more accurate than the between-subject variation in the reported presence measure at recording real differences in presence.
A concern was that a learning effect would result from using the same vection-inertial phase angle for all trials. This concern appears to be unfounded. Ten out of 12 of the participants believed that the phase angle varied between trials, with one more uncertain. (Additionally, all 4 of the participants in Pilot Study AIP4 believed the phase angle varied between trials.) Nor was there a main effect for session number in the ANOVA.
Why did participants not notice the constant phase relationship? One possibility is as follows. As the inertial amplitude dropped, the visual influence on the sense of motion increased, which made it more difficult to distinguish the inertial from the visual self-motion cues. This may have been interpreted as a decrease in the vection-inertial phase difference. Consistent with this (as mentioned at the end of Section 4.2.1), participants did not tend to make a sudden jump from inertial to visual dominance, but rather approached the cross-over by signaling progressively further from the inertial peak as the inertial amplitude was lowered.
The continuous approach to the cross-over amplitude is supportive of the view that the sense of presence in an environment is a gradated, rather than all-or-nothing, phenomenon. It is also consistent with research on visual-proprioceptive discrepancies. Welch and Warren , reviewing the literature, report that ``visual bias of proprioception is not an all-or-none phenomenon.''