Fig 1.
Experiment setup and scene overview.
(a) The subject was fit with a motion capture suit, an Oculus DK2, GSR sensors and a Wii remote. Note that this picture was staged with one of the authors for illustrative purposes, during the experiment the lights were off and the projection display, which in the picture presents the point of view of the subject, was not used. (b) Presents an overview of the virtual scene.
Fig 2.
The subject could experience the scene in three different conditions: (1PP) first person perspective; (3PP) third person perspective; or (ALT) be free to alternate between 1PP and 3PP. When in the alternate condition, subject were asked to perform at least 3 perspective switches.
Fig 3.
Overview of the session stages.
(a) First the subject has to reach for targets that can appear either in the air or in the floor (REACH stage); (b) a final target invites the subject to walk to the wood platform (WALK); (c) once on the platform, the subject is asked to feel the edges with their feet (WAIT); (d) finally, the wooden floor beneath the platform collapses, revealing the pit to the subject (OBSERVE). Subjects in the ¬VMT group do not perform these task, instead they watch recordings from the VMT group. The session was followed by the mental ball drop (MBD) task and an embodiment questionnaire.
Table 1.
Embodiment questionnaire applied in the end of each session.
Answers were given in a 7 point likert scale ranging from strongly disagree (-3) to strongly agree (3). The variable response corresponds to the mean score of the associated questions.
Fig 4.
Questionnaire results: Senses of agency and body ownership for the interaction between perspective and multisensory congruence.
Error bars represent the confidence interval of the mean (CI). “*”, “**” and “***” indicate p < .05, p < .01 and p < .001 respectively.
Fig 5.
Questionnaire results: Self-location and threat responses for the main effect of perspective and multisensory congruence.
Error bars represent the confidence interval of the mean (CI). “*”, “**” and “***” indicate p < .05, p < .01 and p < .001 respectively.
Fig 6.
GSR variation time locked to the floor fall event (response in microsiemens).
(left) The green and red shaded areas highlight the time interval used to compute the median GSR preceding (5 to 0 seconds before) and following (1 to 6 seconds after) the floor fall event for each subject. Each line color represents the GSR recording of one subject. The threat caused a statistically significant increase in the GSR response for all 6 combinations of conditions. (right) The difference between the medians is used to indicate the per subject GSR change linked to the threat. A significant difference between 1PP and 3PP was observed.
Fig 7.
Breakdown of the proportion of time spent in 1PP for each stage of the ALT session for VMT and ¬VMT.
Subjects tended to make a balanced use of perspectives in the REACH stage, while favoring 1PP for the following stages. Notably, overall perspective choice has shifted to 1PP once the reaching task was complete. 1PP seems to be preferred by the VMT group when they had to complete the walking task. This was not the case for the ¬VMT group, who had no practical incentive to change perspective at this stage of the session as the task is completed regardless of their actions. The WALK stage was the only one to present a statistically significant difference between the groups, as analyzed with pairwise t-tests (t35 = 2.88, p < .01).
Table 2.
Post-experiment responses for the VMT group.
Values represent the total count of responses in favor of each perspective condition. Most subjects preferred to use 1PP, and felt safer in 3PP. When asked about conditions, subjects thought ALT to be more efficient in the reaching task. ALT was also preferred by more subjects than the other conditions.