## 2 State of the Art  
In their works, the authors use various types of stimuli or tasks to evoke potentials (to provoke the brain to produce certain reactions that are then analyzed in order to identify individual characteristics of the EEG of subjects). The following stimuli (tasks) were used in well-known works:  
1. Breathing task. Subjects close their eyes and focus on their breathing for several seconds (minutes) [5,6]. 2. Imagining movements of body parts (without actually moving them) or reproducing movements for several seconds (minutes) [7]. 3. Audio stimulation [8]: * Mentally singing or pronouncing individual words (phrases). Subjects imagine singing (in silence) for several seconds (minutes);
* Listening to sounds. Subjects close their eyes and listen to a sound tone (or music) for several seconds (minutes). 4. Visual stimulation. This method is the most common and is found in most publications. Many experiments of varying complexity are based on the principle of visual stimulation. It is believed that the occipital areas of the brain are responsible for visual processing (the strongest visually evoked potential (VEP)) [9]. Many studies have focused on evoking the P300 potential (this is a positive deviation with an amplitude of 2-5 \(\upmu\)V with a delay of 300-600 ms after the stimulus is applied) [10]. Analysis of the P300 potential was used to create interfaces for mental password entry by focusing the gaze on symbols (pass-thought). Typically, P300 is measured by analyzing signals from the Fz, Cz, and Pz electrodes of the standard 10-20 arrangement. To detect P300, the signal accumulation principle is used. Before averaging, the EEG signal must be passed through a bandpass filter (usually with a passband of 1-20 Hz) and artifacts (eye movements, etc.) must be removed. Also analyzed are N1 (N100) waves--negative deviations that peak between 90 and 200 ms after the presentation of an unexpected stimulus. Sometimes subjects are asked to imagine an object or abstraction. Each type of stimulus or task activates different areas of the brain (cortex). Therefore, analysis of data from the corresponding electrodes allows us to identify features that characterize a person (either their condition or the action being performed). The cerebral cortex is divided into zones--[PERSON] cytoarchitectonic areas (52 fields are identified). A more detailed brain map containing about 180 functional zones was compiled in 2016 by [PERSON] [11]. The EEG signal is usually described by the concept of rhythmic activity, which is usually classified by frequency, dividing into alpha (8-13 Hz), beta (14-40 Hz), gamma (30-100 Hz), theta (4-8 Hz) and delta (1-4 Hz) rhythms (waves, ranges) [12]. To remove uninformative frequencies, (frequency) filters (Butterworth,Welch) are often used. To highlight EEG features, spectral, correlation and wavelet analysis methods [13], as well as artificial neural networks, are actively used. There are publicly available EEG databases (DEAP, GrazIIIa, Alcoholism, PhysioNet and others) [10; 14]. They contain EEGs obtained under the influence of strictly defined types of stimuli. When developing new methods of identification (authentication) by EEG, these data may not be applicable. In the work [15], a method of identification of the person by parameters of EEG called CERERE (Cognitive Event-RELated Biometric REcognition) was proposed. The principle of its work consists of the assessment of individual reactions to various stimuli (for example, primary visual perception, recognition of familiar faces, taste). A test set of 400 images of the corresponding theme was prepared. A total of 50 volunteers who were asked to choose a visual image password took part in the experiment. The participants were placed in front of the screen in a sound isolation chamber protected from electromagnetic influences. While the stimuli were shown to subjects, a 26-channel EEG and a 3-channel electrooculogram were recorded. The obtained data were used for training.