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