Background: Observing one’s own body has been shown to influence pain perception—a phenomenon called visual analgesia. The effect was originally obtained using a mirror reflection of one’s own hand and later replicated with prosthetic and virtual hands. Most studies show increased pain thresholds during visual analgesia, but the opposite effect can be obtained by inducing ownership illusion over a limb that looks wounded. We tested the hypothesis that a resilient-looking virtual limb would lead to an increased pain threshold.
Methods: Eighty-eight students (Mage = 21.4, SDage = 2.98) participated in a within-group experimental design study (natural hand virtual reality [VR], marble hand VR, and non-VR control). In both VR conditions, a visuo-tactile synchronous stimulation was used to elicit the illusion of embodiment. Pressure pain stimulus was applied to the forearm. Dependent variables were: pressure pain threshold, pain intensity and self-reported embodiment.
Results: There were significant differences between the control condition and the Natural Hand VR (V = 647, p < .0001), and between the control condition and the Marble Hand VR (V = 947.5, p < .005), but not between the Natural Hand and Marble Hand conditions (V = 1428.5, p = .62). Contrary to our predictions, pain threshold was higher in the control condition. Pain intensity differences were not significant.
Conclusions: We obtained a significant effect in the opposite direction than predicted. Such results may mean that the visual analgesia effect is more context-dependent than previously thought. We discuss methodological differences between the paradigm used in this study and paradigms reported in the literature as a possible explanation.