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. 2013 Jul 31:7:438.
doi: 10.3389/fnhum.2013.00438. eCollection 2013.

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

Matteo Martini  1 , D Perez-Marcos, M V Sanchez-Vives
Affiliations

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

Matteo Martini et al. Front Hum Neurosci. .

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.

Keywords: body ownership; multisensory integration; multisensory stimulation; pain modulation; pain threshold; virtual arm; virtual reality.

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Figures

Figure 1
Figure 1
The experimental set-up and the four experimental conditions: the participant saw the virtual environment through the HMD while an experimenter moved her right index finger to move the avatar’s right index finger accordingly. When the heat stimulation provided on the right wrist was felt as painful by the participant, she stopped the stimulation by pressing the button held on her left hand (A). Top view of the posture of participant’s arm resting on the table, matching avatar’s posture (B). The visuo-proprioceptive congruent feedback given by the finger movements and the first-person perspective view of the avatar fostered the embodiment of the virtual limb while the skin color changed into blue (C), red (D), or green (E) as soon as the heat stimulation started increasing in temperature. In the fourth condition, the skin of the virtual arm did not change color but a gray spot on the table turned into red (F).
Figure 2
Figure 2
Columns and vertical error bars respectively stand for group means and standard errors of the pain thresholds in each condition. Asterisks indicate significant comparisons (*p < 0.05; **p < 0.01).
See this image and copyright information in PMC

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