Manipulation of the participants' self-localization in a lying position

Healthy human beings are aware of their current position space and are able to distinguish their own body from that of other persons or objects. This capability arises from a coupling of sensory information with cognitive processes, and leads to a representation of the person's self. However, in some clinical cases these processes fail and a person can feel himself to be outside of his physical body, as in the out-of-body experience. These phenomena are interesting to study as they lend insight to certain aspects of bodily self-consciousness, such as self-localization and self-attribution. These aspects can be experimentally manipulated in healthy participants through exposure to conflicting multisensory input, as has been demonstrated with the creation of an ownership's feeling with rubber hand stroked synchronously with the real hand. Here, we worked on the full body by manipulate the self-localization of healthy participants. We used similar protocols as in the study of Lenggenhager et al. (2007) and Ehrsson (2007b) but with a lying position, rather a seated or standing as in the aforementioned studies, which are the commune position when out-of-body experience occurs. Participants were put in a comfortable lying position and saw an image of their body through 3D head mounted display, recorded by a video camera located two meters above them. By providing different temporal and spatial information about a visual-tactile event (stroking on the participants' back or chest) self-localization and identification could be modified in a predictable way. We measured self-localization using a mental ball dropping task and measured phenomenological aspects using a questionnaire. The results indicated that a significant variations in self-localization occurred during the experiment. As a follow-up study, we used mental imagery (in our case we used fMRI) to study the regions of the brain involved in this illusion