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

Abstract

The remote control of robots(telerobotics) 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. In this study, we aimed to validate the cross-modal congruency effect (CCE) as an objective measure of embodiment under four conditions with different, a priori expected levels of embodiment, and by comparing CCE scores with subjective questionnaire reports. The conditions were (1) a real hand baseline condition, (2) a real hand seen through a telepresence unit, (3) a robotic hand seen through a telepresence unit, (4) and a human-looking virtual hand seen through VR glasses. 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 proposed several factors that may explain this outcome: the degree of spatial uncertainty about the vibrotactile target location, the relative timing of the target and distractor stimuli, the spatial separation between the vibrotactile target and the visual distractor, and the high cognitive workload during the CCT in the VR condition. We also found no evidence to support the hypothesis that the CCE and embodiment scores as assessed by the subjective questionnaire reports are correlated. Based on these findings, it can be concluded that the CCE may not be a robust measure of embodiment. Therefore, it is recommended that future studies focus on other behavioral and physiological measures to quantify embodiment