## 3 Experimental Protocols Design
### Comparison between Different Virtual Environments  
The totality of the scientific works considered among this review included a consistent portion of the experimental protocol based on spatial navigation. Indeed, this aspect is crucially connected to the perception of sense of presence. In this regard, it has to be observed that also the type of virtual environment can play a role within the embodiment perception [32,33]. More specifically, three main environments can be identified among the different considered scientific works:  
* The physical environments, consisting of the representation of the experimental environment in RL. Among the considered scientific contributions, this experimental environment was considered as the gold standard for the embodiment assessment in MR.
* The photographic environment, consisting of the bidimensional representation of the selected experimental environment. This condition was designed by [PERSON] and colleagues [46] for evaluating the sense of presence grade within a bidimensional digitalized environment. * The 360-degree environment, consisting of the tridimensional representation of the selected experimental environment. Again, this condition was proposed by [PERSON] and colleagues [46] and [PERSON] and colleagues [47] for assessing embodiment in the static tridimensional environment, which was hypothesized to lead to an increase of the sense of presence with respect to the static bidimensional representation. * The VR environment, consisting of the virtual and interactive representation of the selected experimental environment. This condition was selected by the totality of the considered scientific works. * The AR environment, consisting of the integration of digital elements, typical of VR environments, with physical elements, typical of the RL environment. Such a condition was included in the experimental design of the large majority of the considered scientific papers within the present review [5; 12; 27; 43; 44; 47; 48; 49]. Among the approaches proposed by the considered scientific works, [PERSON] and colleagues [50] investigated the cortical activity modulation in 2D versus 3D virtual reality environments. In this context, the bidimensional and tridimensional virtual environments were compared in terms of cortical activity modulation, in order to derive relevant insights regarding the embodiment of the participants. More specifically, the participants were exposed to a virtual corridor and navigated through it using a wireless joystick to reach a specific location within the target room. This task was divided into two phases: the encoding phase, during which participants were shown the navigation route to memorize, and the retrieval phase, during which they navigated to the position of the target room. Concerning the comparison between static and interactive virtual environments, [PERSON] and colleagues [38] proposed research for evaluating the neural correlates changings when executing exposure tasks at height in VR, RL, and photographic environments. In particular, the researchers exposed the participants to a height of 33 m in the RL condition through a fire truck's cherry picker. Analogously, such a condition was replicated in VR, through 3D-360\({}^{\circ}\) videos, and in bidimensional images provided through a PC screen. Similarly, [PERSON] and colleagues [43] investigated the neurophysiological embodiment of participants when performing a spatial navigation task coupled and not coupled with height exposure. In this context, the experimental protocol foresaw the comparison between the VR and RL conditions. Other approaches in scientific literature were identified in the gaming context. In this regard, [PERSON] and colleagues [51] proposed a comparison between VR and a bidimensional environment representation, provided through a PC desktop screen, in terms of sense of presence perceived by the players. Further interesting research on the embodiment neurophysiological characterization were focused on the Brain Computer Interface (BCI) applications [52; 53].