Setup, electrocardiogram (ECG), signal analysis

The present protocol adapted an experimental setup described previously⁴³. Participants stood with their backs facing a video camera placed 2 metres behind. The video, showing the participant’s body (virtual body) was projected in the body conditions in real time onto a head mounted display (HMD), see Fig. 4. While filming the video we also recorded the participant’s ECG throughout the entire experiment. Raw data (ECG) were acquired with the BioSemi Active II™ system (BioSemi, The Netherlands) at a sampling rate of 2048 Hz. In-house software (http://lnco.epfl.ch/expyvr) was developed to detect, in real time, the peak of each R-wave from the recorded ECG data and to trigger an additional visual stimulus (e.g. a flashing outline surrounding the participant’s virtual body) that flashed on and off synchronously or asynchronously with respect to the participant’s heartbeat (for further details please refer to Fig. 4). There were 2 different blocks corresponding to 2 different conditions: (1) Body with flashing outline synchronous with the heartbeat (body synchronous, BS); (2) Body with flashing outline asynchronous with the heartbeat (body asynchronous, BAS). Because of limited space in the faraday cage we were not able to test an object control condition.

Setup. Participants (a) stood with their backs facing a video camera placed 200 cm behind them (b). An electrocardiogram was recorded (a) and R-Peaks were detected in real-time (c), triggering a flashing silhouette outlining the participant’s body (virtual body) (d). The video, showing the virtual body was projected in real time onto a head mounted display (HMD) (body condition). It appeared visually that the virtual body was standing 200 cm in front of the participant (e).