Kaplan, Alexander Ya.

Relevance. Brain-computer interface (BCI) technology is widely employed in studies focused on possibility of substitution of human verbal and motor communication channels when such channels are lost due to stroke or trauma. One of the most promising examples of BCI technology is P300 BCI – a system based on P300 component of visual evoked potential. Visual stimulation plays a key role in P300 BCI concept, and it is thus important to explore the influence of visual stimuli environment on user’s eye movements and BCI performance.

Objective. The objective was to explore the influence of the main components of P300 BCI visual environment, namely matrix stimuli size and spacing, on the movements of user's eyes during typing, the accuracy of typing, and the amplitude and latency of P300 component.

Methods. Sixteen healthy subjects were recruited for the study. Each subject participated in five experimental sessions, where P300 BCI matrix stimuli size and spacing varied from 1.22 and 0.73 to 2.43 and 1.45 degrees of visual angle. During each experimental session, subjects were typing in a certain text sequence using the BCI while their eye movements and EEG were being recorded.

Results. We found that the stimuli size significantly affected certain characteristics of user’s eye movements. The stimuli size and spacing, however, had no significant effect on the accuracy of the typing and the amplitude and latency of P300 component.

Conclusions. The results of the study can prove to be beneficial to the development of efficient visual stimuli environments for P300 BCI.

Relevance. P300-based brain-computer interface (P300 BCI) enables a user to choose commands by consciously attending to certain visual stimulus. However, P300 BCI-based systems for detection of covert focuses of human interest, including emotional stimuli, can be built and applied in systems for monitoring human’s normal and pathological state.

Objective. The objective was to investigate the properties of perception of stimuli with different subjective emotional significance for the person and to evaluate the possibility of P300 BCI-based detection of covert emotional focuses of attention.

Methods. 14 healthy subjects participated in the EEG-study with consequent presenting of visual stimuli with emotional or neutral human faces photos. In the first block the participants’ task was just to look at the screen with appearing stimuli (passive attention) while one of six stimuli in each trial was emotional. In the other two blocks the task was to silently count the number of the target stimulus presentations among non-target stimuli (active attention) with emotional or neutral target stimulus depending on the block. We analyzed the event-related potentials (ERP) for stimuli of different classes and the classifica-tion accuracy for target (or emotional) stimulus in P300 BCI-similar fashion.

Results. In this study we showed that the accuracy of presented in passive viewing paradigm emotional stimuli recognition exceeded the random level more than twice. Also we found characteristic features of the potentials in response to stimuli with various significance.

Conclusions. The obtained results create opportunities for developing the clinically applicable P300 BCI-based systems for detection of covert attentional focuses.