## 6 Neurophysiological Characterization of Embodiment in Mixed Reality
### Equipment Selection for Neurophysiological Signals Collection  
As introduced in the first section of the present review, in the context of MR research, the acquisition of neurophysiological signals such as EEG, ECG, PPG, and EDA is crucial for objectively understanding participants' experiences, particularly embodiment. Many studies used moderately high-density EEG devices for data recording. Notably, the Brain Products actiCAP EEG System (Brain Products GmbH, Gilching, Germany) was frequently employed to assess the sense of presence in VR and AR environments [57]. The system offers flexible configurations with up to 256 channels, enabling researchers to capture detailed brain activity with high spatial resolution. To meet MR HMD compatibility and wearability requirements, the studies typically used a maximum of 32 active electrodes arranged according to the international 10-20 system. Similarly, the Neuroelectrics Enobio (Neuroelectrics, Barcelona, Spain) was also chosen to investigate neural correlates of embodiment in MR [57]. Such a system was equipped with up to 32 EEG channels, and it was consistently employed for its capability for real-time synchronization with AR and VR environments. In this context, also high-density EEG systems were employed for objective embodiment characterization. [PERSON] and colleagues [61] selected the Neuroscan SynAmps RT amplifiers by Compumedics and a fabric cap with integrated electrodes (Electro-Cap International) equipped with 60 active gel-based EEG channels, positioned according to the 10-10 system. Similarly, [PERSON] and colleagues [60] employed g.USB-Amp amplifiers (g.tec medical technologies, Austria) and 57 active electrodes for measuring the emotional impact on the sense of presence within the VR environment. Conversely, other recent scientific works were conducted by employing low-density EEG systems. Such systems consistently advanced in terms of performance and accuracy in recent years, and they are the most compatible with out-of-the-lab applications, such as the ones focused on MR approaches, since their invasiveness grade is minimal. In this regard, different recent scientific works were performed by selecting the Emotiv EPOC+ device [45; 59]. Such a system was equipped with 14 water-based EEG channels, and it \begin{table}
\begin{tabular}{c c c} \hline \hline
**Behavioural Parameter** & **Definition** & **Experiments** \\ \hline Latency time & Time period between an input or stimulus and the participant’s behavioral response. & 11 \\ \hline Transversal time & Duration required to complete a specific task or action within the virtual environment. & 5 \\ \hline Discomfort response time & Time period for obtaining the participant’s response to a stressful stimulus. & 6 \\ \hline Walking time & Time period required for completing spatial navigation tasks in MR. & 12 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of the behavioral parameters related to the embodiment assessment in Mixed Reality identified among the considered scientific literature. offered compatibility with Unity and Unreal Engine, facilitating integration with AR and VR applications for immersive research experiences. Other crucial neurophysiological signals for the objective embodiment assessment in MR are the ones deriving from cardiac activity (i.e., ECG and PPG). More specifically, among the different considered scientific contributions, the ECG signal was collected through the usage of a various range of equipment directly connected to the EEG amplifier. In this regard, [PERSON] and colleagues [38] selected three active sensors connected via a BIP2 AUX adapter by Brain Products. Similarly, [PERSON] and colleagues [48] employed EKG ProComp+ sensors by Thought Technologies Ltd. on the torso. More wearable solutions were selected within more recent scientific approaches by collecting the PPG signal.