## 2 Material and Methods
### Research on VR-BCI Systems
Researchers analyze brainwave patterns such as the following: * Brain rhythms: Alpha waves (8-12 Hz)--elevated can be used to signal relaxation or lack of engagement, while decreased can indicate increased attention or mental effort; Beta waves (13-30 Hz)--increased beta activity can be used to detect states of increased attention or engagement; * P300 event-related potential--a characteristic brain response to a rare or unexpected stimulus (positive, 300 ms delayed), used for selection tasks; * Steady-state visually evoked potentials--elicited by flickering stimuli at specific frequencies, allowing for control by focusing attention; 2. Functional near-infrared spectroscopy (fNIRS) [54; 55]--measures brain activity by detecting changes in blood oxygenation. Offers better spatial resolution than EEG but is more limited in terms of portability; 3. Functional magnetic resonance imaging (fMRI) [56]--provides high spatial resolution images of brain activity but is expensive, immobile, and not suitable for real-time BCI-VR applications. VR systems include the following:  
1. Head-mounted displays [3; 52; 53]--immersive VR experiences, often combined with head tracking for more natural interaction; 2. Desktop VR [57]--less immersive but more accessible and affordable; 3. CAVE systems--highly immersive, multi-projection VR environments, but expensive and less common. Experimental paradigms include the following:  
1. Motor imagery--participants imagine performing movements to control virtual objects or navigate environments [52];Visual attention--participants control the VR environment by focusing their attention on specific stimuli [58];
* Cognitive tasks--BCI systems can be used to assess cognitive function in VR environments, such as memory, attention, and decision-making [54]. Data analysis and classification include the following: 1. Signal processing--extracting relevant features from noisy brain signals [59];
* Machine learning--training algorithms to classify brain patterns and translate them into control commands [59];
* Statistical analysis--evaluating the performance and usability of BCI-VR systems. User experience evaluation includes the following: 1. Questionnaire--assessing subjective experiences like presence, embodiment, and usability [52; 53];
* Performance metrics--measuring task accuracy, completion time, and other objective indicators of system performance [4]. Ethical considerations are paramount in any research involving human participants. In the context of our studies, which focus on healthy users rather than patients, formal approval from an institutional review board or ethics committee was not sought. This decision aligns with ethical guidelines for research involving non-clinical populations and minimal-risk procedures. Participation in the experiment was entirely voluntary, with each participant providing informed consent after receiving a comprehensive explanation of the study's objectives, procedures, and potential risks and benefits. Participants were explicitly informed of their right to withdraw from the study at any time without consequence. Data collected during the study was anonymized to protect participant privacy and confidentiality.