Distortion Of The Perceived Body Image By Asynchronous Visuo-Tactile Stimulation
Naturally or artificially-induced multisensory correlations may yield perceptual distortions or body-related illusions. For instance, it is known that during the rubber hand illusion (RHI), an external fake limb can be “embodied” within the subject's body image by means of synchronous multisensory stimulation. While the asynchronous condition has traditionally been considered just as a control, some authors recently pointed out that it can evoke an experience of “deafferentation” of the affected limb. Similarly, previous studies have reported a distortion in the self-estimated body image in case of limb deafferentation in locally anesthetised patients. Here we examined the possible body asymmetries induced by either synchronous or asynchronous visuo-tactile stimulation within the experimental paradigm of the RHI. We stimulated the left and the right hands alternatively every 20s, one hand receiving synchronous and the other hand asynchronous visuo-tactile stimulation. Before and after the RHI, participants completed a task for assessing the own body image. We observed a significant elongation in the perceived relative forearm length after the RHI, specific for the asynchronously stimulated side. A high sense of ownership of the rubber hand maintained the perceived limb length constant. Thus, the present results suggest that a very short stimulation (~40s in total) was effective to get a lateralized plastic rearrangement in the representation of one's own body. Indeed, we foster the hypothesis that the asynchronous multisensory stimulation would yield a sort of deafferentation of the interested body part, leading then to a distortion of the internal representation of that body part. This would be in agreement with data from patients undergoing local anaesthesia who perceived the deafferented body part longer (Paqueron et al., 2003).
This research was supported by FP7 EU collaborative projects BEAMING (248620) and VERE (257695).