BEING PRESENT IN A REAL OR VIRTUAL WORLD: A EEG STUDY Abstract   Background and objective  This study proposes an approach to evaluation and measuring of presence for manmachine interaction in the virtual reality based on electroencephalographic data.    Materials and methods  It analyzes stable electroencephalographic patterns that allow us to trace a connection between a brain activity and purposeful actions of an individual in various environments. The subjects of the study were experienced downhill skiers equipped with electroencephalographs, who performed reallife skiing on a downhill course, after which they were offered a virtual simulation of downhill skiing using an HTCVive headset and a programmed 2D or desktop simulator.    Results  The results of measurement showed neuropatterns similar in the cases of virtual reality simulation and physical downhill skiing (in part of changes in space and power parameters of electroencephalograms in the different frequency ranges) and different from a 2D simulator. This observation enables us to make an assumption of realism of a virtual reality simulator in the context of reproduction of the subjectsu0027 similar cognitive and semantic connections and motor programs.    Discussion  Further research work will focus on evaluation of efficiency in performing psychophysiological tests (time response to a mobile object) in the virtual reality and 2D desktop application.

Using Virtual Reality to Examine the Correlation between Balance Function and Anxiety in Stance We study the interaction between balance function and anxiety in humans via a virtual reality based experimental setup, fundamentally designed to examine postural control and neurological feedback during balancedemanding height and perturbation shifts, while in quiet stance. In this work, sensory organization balance test (SOT) was utilized to quantify the balance function in subjects, and the salient features of the recorded electrocardiogram (EKG), electromyogram (EMG) and electroencephalography (EEG) signals described the subjectu0027s physiological anxietyrelated responses. Also, patientreported outcomes measurement information system (PROMIS) trait anxiety questionnaire was adopted to indicate the selfassessed trait anxiety scores by the subjects. Our statistical analysis indicates that subjects with higher SOT scores encounter a lower heart rate variability during baseline recording relative to the experimental trials and lower cocontraction index of the ankle dorsiflexion (during the experimental trials), suggesting a lower anxiety state. A similar trend was further observed via the selfreported PROMIS questionnaire responses, estimating anxiety experienced in daily life. Additionally, we utilize machine learning to describe the predictability of balance function states via the relative  alpha band power from the frontal channels of the recorded EEG signals as descriptive features characterizing anxiety. The discussed trends analytically demonstrate the potential for adopting balance function to anticipate anxiety, especially in stressful environments involving postural threats.