Measuring Visual Fatigue and Cognitive Load via Eye Tracking while Learning with Virtual Reality Head-Mounted Displays: A Review

In this paper, I address the question as to why participants tend to respond realistically to situations and events portrayed within an immersive virtual reality system. The idea is put forward, based on the experience of a large number of experimental studies, that there are two orthogonal components that contribute to this realistic response. The first is 'being there', often called 'presence', the qualia of having a sensation of being in a real place. We call this place illusion (PI). Second, plausibility illusion (Psi) refers to the illusion that the scenario being depicted is actually occurring. In the case of both PI and Psi the participant knows for sure that they are not 'there' and that the events are not occurring. PI is constrained by the sensorimotor contingencies afforded by the virtual reality system. Psi is determined by the extent to which the system can produce events that directly relate to the participant, the overall credibility of the scenario being depicted in comparison with expectations. We argue that when both PI and Psi occur, participants will respond realistically to the virtual reality.

Trials of virtual reality exposure therapy (VRET) for anxiety-related disorders have proliferated in number and diversity since our previous meta-analysis that examined 13 total trials, most of which were for specific phobias (Powers & Emmelkamp, 2008). Since then, new trials have compared VRET to more diverse anxiety and related disorders including social anxiety disorder (SAD), posttraumatic stress disorder (PTSD), and panic disorder (PD) with and without agoraphobia. With the availability of this data, it is imperative to re-examine the efficacy of VRET for anxiety. A literature search for randomized controlled trials of VRET versus control or in vivo exposure yielded 30 studies with 1057 participants. Fourteen studies tested VRET for specific phobias, 8 for SAD or performance anxiety, 5 for PTSD, and 3 for PD. A random effects analysis estimated a large effect size for VRET versus waitlist (g = 0.90) and a medium to large effect size for VRET versus psychological placebo conditions (g = 0.78). A comparison of VRET and in vivo conditions did not show significantly different effect sizes (g = -0.07). These findings were relatively consistent across disorders. A meta-regression analysis revealed that larger sample sizes were associated with lower effect sizes in VRET versus control comparisons (β = -0.007, p <  0.05). These results indicate that VRET is an effective and equal medium for exposure therapy.