The cross-modal congruency effect as an objective measure of embodiment

Remote control of robots generally requires a high level of expertise and may impose a considerable cognitive burden on operators. A sense of embodiment over a remote-controlled robot might enhance operators? task performance and reduce cognitive workload. We want to study the extent to which different factors affect embodiment. As a first step, we aimed to validate the cross-modal congruency effect (CCE) as a potential objective measure of embodiment under four conditions with different, a priori expected levels of embodiment, and by comparing CCE scores with subjective reports. The conditions were (1) a real hand condition (real condition), (2) a real hand seen through a telepresence unit (mediated condition), (3) a robotic hand seen through a telepresence unit (robot condition), and (4) a human-looking virtual hand seen through VR glasses (VR condition). We found no unambiguous evidence that the magnitude of the CCE was affected by the degree of visual realism in each of the four conditions. We neither found evidence to support the hypothesis that the CCE and embodiment score as assessed by the subjective reports are correlated. These findings raise serious concerns about the use of the CCE as an objective measure of embodiment.