Immersive Virtual Reality and Virtual Embodiment for Pain Relief

Abstract

A significant body of experimental evidence has demonstrated that it is possible to induce the illusion of ownership of a fake limb or even an entire fake body using multisensory correlations. Recently, immersive virtual reality has allowed users to experience the same sensations of ownership over a virtual body inside an immersive virtual environment, which in turn allows virtual reality users to have the feeling of being "embodied" in a virtual body. Using such virtual embodiment to manipulate body perception is starting to be extensively investigated and may have clinical implications for conditions that involve altered body image such as chronic pain. Here, we review experimental and clinical studies that have explored the manipulation of an embodied virtual body in immersive virtual reality for both experimental and clinical pain relief. We discuss the current state of the art, as well as the challenges faced by, and ideas for, future research. Finally, we explore the potentialities of using an embodied virtual body in immersive virtual reality in the field of neurorehabilitation, specifically in the field of pain.

Keywords: body illusion; embodiment; ownership illusion; pain; virtual reality.

Figures

FIGURE 1

Experimental setups for (A) the rubber hand illusion (RHI), (B) the virtual hand illusion in non-immersive virtual reality, and (C) the virtual hand illusion in immersive virtual reality. Part (C) taken from Martini et al. (2015), reprinted with permission from Springer Nature.

FIGURE 2

Experimental setup and results from Longo et al. (2009) in which vision of the body was shown to be analgesic, subjectively (using self-report pain ratings) and objectively using laser-evoked potentials. (A) The mirror box technique in which the subject has the experience of viewing their right hand, while in fact seeing their left hand reflected in a mirror. (B) Laser-evoked potentials (left) and peak-to-peak amplitudes (right) for the three experimental conditions. Error bars are one SEM. Reprinted from Copyright [2009] Society for Neuroscience. ∗p < 0.05, ∗∗p < 0.01.

FIGURE 3

(A) Experimental setup of co-location experiment by Nierula et al. (2017). The participant wore a head-mounted display that provided an immersive virtual environment including a virtual own body that was perceived from a first-person perspective. The transparent arm outlined with a white dashed line indicated the positions of the virtual arm. Position of participant during (left panel) co-location, where the virtual and real arm were co-located, and (middle panel) when there was a distance of 30 cm between the real and virtual arm (right panel). The virtual body from the participant’s point of view. Reprinted with permission from Elsevier. (B) Participant’s view of virtual arm in the experiment by Martini et al. (2013). The right arm is co-located with the virtual arm, with congruent finger movements, in order to induce embodiment of the virtual limb. Heat stimulation is provided to the wrist while the skin color changed. Pain threshold was increased in the blue arm condition (left) versus the red arm condition (right).

FIGURE 4

Experimental setup, and transparency and size tests for Matamala-Gomez et al. (2018). (A) Patients wore a head-mounted display (HMD) that immersed them in a virtual environment, which allowed participants to feel embodied in a virtual body viewed from a first-person perspective that was co-located with their real body. Virtual balls tapped the fingers during each stimulus presentation, which was accompanied by visuo-tactile stimulation to induce ownership over the virtual arm. (B) Transparency test including all four conditions: virtual arm transparency set at 0% (maximum opacity), 25, 50, and 75% (low opacity). (C) Size test including all three conditions: virtual arm presented in a big size, in its normal size, and in a small size. Reprinted with permission from Elsevier.