Discussion
HMD, pain
HEAT
In the current study we used real water to give virtual objects (i.e., animated virtual water) more realistic physical properties (wet liquid qualities). As predicted, compared to reaching their virtual hand into the computer-generated virtual water with no tactile feedback (as their real hand reached into the air), adding real water to the immersive VR experience significantly increased VR analgesia (r = 0.5, a large effect size), increased the illusion of presence, increased avatar (virtual hand) embodiment, increased how much fun participants had during the pain stimulus, and increased how real the computer generated virtual water felt to the subjects. Compared to “No VR”, “VR + Yes Real Water” reduced worst pain by 35% in the current study. This 35% reduction in worst pain is consistent with our previous results showing that VR analgesia can be comparable to the opioid analgesia from a moderate dose of hydromorphoneIn the current study, as predicted, we also observed a significant correlation between how present participants felt during VR + real water, and how much their pain was reduced during VR + real water. In addition, on a divided attention task, going into VR during the odd number task significantly increased the number of errors made on the odd number task during each VR condition, and participants reported that they found it significantly more distracting and more difficult to concentrate on the odd number task during VR than performing the odd number task with “No VR”. Contrary to predictions, although in the predicted direction, adding tactile feedback did not significantly reduce accuracy on the odd number task, or participants’ ratings of how much VR distracted them during the odd number task.In the current study, we measured conditioned pain modulation. Participants reported significant reductions in the worst pain they felt on their “foot only” (the target stimulus) when they also received a simultaneous thermal heat pain stimulus to their wrist, (a conditioning pain stimulus). This reflects a functioning endogenous pain modulation system. In addition to “pain reduces pain” reductions in worst pain (i.e., significant CPM for worst pain, a measure of the sensory component of pain), the current study found that CPM was also significant for pain unpleasantness (a measure of the emotional component of pain), and time spent thinking about pain (a measure of the cognitive component of pain). Interestingly, analyses indicate a significant correlation between how much VR + real water reduced worst pain ratings, and the reduction in worst pain during conditioned pain modulation.According to Hoehn et al.Overall, the results of this study implicate an attentional mechanism for how VR reduces pain. The results help understand how VR influences pain perception, and help guide the design of more immersive and more effective VR analgesia treatments in the future.A number of experimental studies have now shown that increasing the immersiveness of the VR system increases the illusion of “being there” and/or increases VR analgesia for acute pain by increasing the field of view seen through the HMD, and by adding avatars and/or increasing interactions with visual only virtual objects