Introduction
hand movements, burn injuries, HMD, pain
CORTEX
Excessive pain during medical procedures is a worldwide medical and healthcare/psychological problem, for example, pediatric burn wound careA number of psychological factors such as catastrophizingDuring burn wound care with immersive VR, a Head Mounted Display, (HMD) blocks the patient’s view of the real world, so the patient is not able to see the hospital room and is not able to watch their wound care. Instead, patients see and interact with a pleasant computer-generated environment (e.g., SnowWorld) that is completely unrelated to their injury and unrelated to their painful medical procedure, allowing patients to mentally “escape” from their pain into the pleasant computer generated world. We theorize that during VR, multisensory computer generated information floods into the patients’ brain through their sensory systems (e.g., the visual cortex) and interferes with the brain’s conversion of nociceptive signals into the patients’ conscious experience of pain, reducing pain-related brain activity, and reducing the perception of pain. Children recovering from large severe burn injuries report large reductions in pain while they are in VR, the patients indicate spending less time thinking about their pain during VR, and even report having fun during wound care while in virtual realityThe essence of immersive virtual reality is the participants’ illusion of “being there” in the computer generated environment, as if the virtual world is a place they are visiting, an illusion known as “sense of presence”. It is assumed that a stronger illusion of presence is associated with more attentional resources being drawn into the virtual world, leaving less attention available to process nociceptive signals, thus reducing the perceived experience of pain (i.e., an attentional mechanism). Although the mechanism of how VR reduces pain is not well understood, consistent with the hypothesis of an attentional mechanism, experimental studies have shown that an increase in the immersiveness of the VR system (e.g. increasing the field of view participants see through the HMD, increasing interactivity and/or adding avatars) can significantly amplify how much VR reduces painThe current experimental pain study with healthy volunteers explored whether adding physical properties (wet physical liquid tactile sensations) to virtual objects (computer generated animated water seen through the HMD) would increase the analgesic effectiveness of virtual reality as a non-opioid pain reduction technique. Immersive VR mixed reality techniques involving co-locating real and virtual objects (i.e. tactile augmentation)In the current study, using a camera-based hand tracking system with a first person perspective, participant’s real hand movements were mimicked by their corresponding “visual only” virtual avatar hands seen through the VR Head Mounted Display (HMD). In addition to increasing VR analgesia, we assumed that participants would report a stronger illusion of presence, and greater ownership/embodiment of their virtual avatar hands during the more immersive “mixed reality” (avatar VR + real water), compared to touching virtual water only (no real water/no tactile feedback) and we predicted a significant correlation between sense of presence in VR, and the amount of pain reduction during VR with tactile feedback. With respect to other mediating factors, we predicted that participants would make more errors on a divided attention task during VR, (an objective measure of how much attention VR diverts) and we predicted that these errors would be enhanced in the mixed reality VR condition. Moreover, we predicted that conditioned pain modulation, an important measure of endogenous pain inhibition, would be related to analgesia when participants were immersed in the virtual reality scenario and were receiving the tactile feedback from the virtual water (i.e., analgesia during the VR + real water condition).