## 3 Experimental Protocols Design
### Comparison between Different Virtual Environments
In this regard, it has to be considered the relevant contribution associated with the research proposed by [PERSON] and colleagues [33], which investigated the perceived embodiment by participants while dealing with BCI in immersive VR. In particular, such experimental protocol foresaw the control of a virtual arm with brain activity on the computer screen and through an HMD for VR, and the control of the same virtual arm through the actual arm movements with an HMD. A second relevant branch of experimental design related to the neurophysiological embodiment characterization in MR corresponds to the avatar control-based tasks. This paradigm aims to investigate how individuals perceive and interact with avatars or virtual bodies within MR settings. In this regard, [PERSON] and colleagues [54] investigated the EEG-based measurement of embodiment when controlling a walking self-avatar. More specifically, the experimental protocol foresaw that participants were instructed to either physically control the movements of a virtual avatar in real time, mentally simulate the avatar's movements without physical action, or simply observe the avatar's movements. This multifaceted approach allowed researchers to explore the nuances of embodiment and motor imagery within a MR setting. A second interesting research in this context was performed by [PERSON] and colleagues [32]. They designed an experimental protocol for errors monitoring in the actions of an avatar seen from a first-person perspective. In particular, the participants in the study were engaged in an immersive setup, consisting of a virtual dining room with two mugs on a table, observed through HMD. The virtual environment featured two avatars, one in first-person perspective and the other in third-person perspective. Therefore, this experimental design assessed the neurophysiological embodiment through error monitoring while executing the requestedactivity in MR in first-person perspective and in third-person perspective. A similar approach was performed by [PERSON] and colleagues [27], who designed an experimental protocol for assessing the neural correlates associated with embodiment while performing movement of a digital wrist when the immersivity within the virtual environment was broken. More specifically, the experiments foresaw the disruption of the wrist movement representations within the virtual environment. Such a condition followed a monitoring phase in which participant embodiment was evaluated while performing the digital wrist movements within a coherently responding virtual scenario. Finally, another relevant aspect characterizing the experimental scenario consists of the impact of social entities within the virtual environment on embodiment. In fact, human beings are inherently social creatures, and our interactions with others profoundly influence how we perceive ourselves and our surroundings. In MR, the presence of social entities, such as virtual avatars representing other individuals or artificially intelligent agents, can enhance or diminish the sense of embodiment. This aspect was investigated by [PERSON] and colleagues [55] by performing an experimental protocol in which the participants' perceptions of agents across different conditions was evaluated, with a focus on the level of responsiveness exhibited by these agents and how it influenced participants' treatment of them as either social entities or mere objects. Practically, the experimental design foresaw the interaction with a virtual agent behaving differently (i.e., static, moving, responsive, and talking conditions). A consistent similar approach was conducted by [PERSON] and colleagues [48], who investigated the threat perception impact on embodiment in MR when interacting with an avatar who differently behaved in four experimental conditions (i.e., static, moving, responsive, and talking conditions). The following Table 1 resumes the different MR experimental scenarios investigated by the scientific literature considered through this review: