What Color is My Arm? Changes in Skin Color of an Embodied Virtual Arm Modulates Pain Threshold

Abstract

It has been demonstrated that visual inputs can modulate pain. However, the influence of skin color on pain perception is unknown. Red skin is associated to inflamed, hot and more sensitive skin, while blue is associated to cyanotic, cold skin. We aimed to test whether the color of the skin would alter the heat pain threshold. To this end, we used an immersive virtual environment where we induced embodiment of a virtual arm that was co-located with the real one and seen from a first-person perspective. Virtual reality allowed us to dynamically modify the color of the skin of the virtual arm. In order to test pain threshold, increasing ramps of heat stimulation applied on the participants’ arm were delivered concomitantly with the gradual intensification of different colors on the embodied avatar’s arm. We found that a reddened arm significantly decreased the pain threshold compared with normal and bluish skin. This effect was specific when red was seen on the arm, while seeing red in a spot outside the arm did not decrease pain threshold. These results demonstrate an influence of skin color on pain perception. This top-down modulation of pain through visual input suggests a potential use of embodied virtual bodies for pain therapy.

Real, rubber or virtual: The vision of “one’s own” body as a means for pain modulation. A narrative review

“…The physical appearance of the body may also play a significant role. Indeed the vision of a distorted body appearance may modulate the body ownership levels , but it may also affect psychological factors such as body image and modulate pain perception during illusory body ownership paradigms (Martini et al, 2013Osumi, Imai, Ueta, Nakano, et al, 2014; or in studies involving the vision of one's own real body (Mancini et al, 2011;Romano & Maravita, 2014).…”

“…What seems to be a key factor in driving the modulation of pain is the expectation created by the body-related visual input. For instance, in an experiment using visual manipulations of the virtual body and heat pain threshold, changes in colour of the virtual arm differently drove the pain threshold of the participants according to the kind of colour displayed: the vision of a bluish ''cold" arm led to a higher pain threshold as compared to a reddish ''hot" arm, while a neutral green arm stood right in the middle (Martini, Perez-Marcos, & Sanchez-Vives, 2013). Exploiting the powerful association that colours have with temperatures, the vision of one's own arm changing colour triggered top-down processes that differently modulated pain perception (Martini et al, 2013).…”

Behavioral, Neural, and Computational Principles of Bodily Self-Consciousness

“…Thus, visuo-tactile integration inducing the rubber hand illusion is subject to the constraints determining multisensory integration within the PPS (see Figure 1C). Illusory ownership can also be evoked for a very long virtual arm (Kilteni et al, 2012;Armel and Ramachandran, 2003) or different arm colors (Martini et al, 2013), pending that the virtual limbs were perceived to be connected to the participant's body (Perez-Marcos et al, 2012). In addition, illusory hand ownership occurs not only when visuo-tactile stimulation on the participant's hand and on the virtual hand are perfectly synchronized, but also with a delay shorter that 300 ms, whereas at higher delays the strength of the illusion decays and vanishes for delays longer than 500 ms (Shimada et al, 2009; see also Aspell et al, 2010 andZopf et al, 2010 for temporal factors affecting multisensory interaction during the full-body illusion and the rubber hand illusion, respectively).…”

The Dream is Collapsing

“…For example, literature explores changes in perception arising from making people old or young [4], black or white [24], or short or tall [45].…”