Vicarious pain is an outcome of atypical body ownership: evidence from the rubber hand illusion and enfacement illusion

Some people report localised pain on their body when seeing other people in pain (sensory-localised vicarious pain responders). In this study we assess whether this is related to atypical computations of body ownership which, in paradigms such as the Rubber Hand Illusion (RHI), can be conceptualised as a Bayesian inference as to whether multiple sources of sensory information (visual, somatosensory) belong together on a single body (one’s own) or are distributed across several bodies (vision=other, somatosensory=self). According to this model, computations of body ownership depend on the degree (and precision) of sensory evidence, rather than synchrony per se. Sensory-localised vicarious pain responders exhibit the RHI following synchronous stroking and – unusually – also after asynchronous stroking. Importantly, this occurs only in asynchronous conditions in which the stroking is predictable (alternating) rather than unpredictable (random). There was no evidence that their bottom-up proprioceptive signals are less precise, suggesting individual differences in the top-down weighting of sensory evidence. Finally, the Enfacement illusion (EI) was also employed as a conceptually-related bodily illusion paradigm that involves a completely different response judgment (based on vision rather than proprioception). Sensory-localised responders show a comparable pattern on this task after synchronous and asynchronous stroking. This is consistent with the idea that they have top-down (prior) differences in the way body ownership is inferred that transcends the exact judgment being made (visual or proprioceptive)