Incorporation of prosthetic limbs into the body representation of amputees: Evidence from the crossed hands temporal order illusion.

Understanding how we consciously experience our bodies is a fundamental issue in both psychology and neuroscience. To date, the incorporation of nonbody objects into the body representation has been investigated extensively, and the incorporation of prosthetic arms in amputees has been demonstrated using the rubber hand illusion. In this study, we investigated the incorporation of prosthetic arms in amputees using the crossed hands illusion, in which successive somatosensory stimuli are delivered, one to each arm, at intervals of 300ms or less, and where arm crossing often causes inversion of perceived tactile temporal order. The induced reversal illusion was greater with a prosthetic limb than without in three amputees. With a shorter prosthetic arm (i.e., one that did not reach the contralateral limb), the illusion induced by vision of the short prosthetic arm was significantly reduced as compared to that seen when the long prosthetic arm crossed over the other arm. These results therefore suggest that the somatosensory signals were referred to the spatial location of the tips of the prosthetic arm, which was incorporated into the body representation by the amputees.