# Monitoring Brain State and Behavioral Performance during Repetitive Visual Stimulation
###### Abstract
In particular, attention, a fundamental aspect of the observer's state, modulates prestimulus alpha- and beta-band power [9; 10; 11], influencing the accuracy of perceptual decisions. Thus, either medium or low alpha- and high beta-band power during the prestimulus period is beneficial for sensory perception [11; 12]. According to [13], the power and the prestimulus EEG phase coupling in the alpha- and beta-bands affect visual perception performance. Namely, better performance is associated with low phase coupling in the alpha-band and high phase coupling in the beta-band. Recent work [14] revealed that EEG power in the beta-2 frequency band at rest negatively correlated with the response times in the ongoing attentional task. While most works reported correlations between the neural correlates averaged across the trials, or between event-related potentials, in recent work [15], the authors used EEG power in different bands to predict individual performance in single trials contributing to the BCI problem. Complementing the existing literature, we examined how the prestimulus EEG power predicts behavioral performance depending on the task demands. We considered a long-lasting monotonous experiment in which the participant perceived ambiguous stimuli and reported on each stimulus interpretation with the joystick buttons. The visual stimulus was an ambiguous Necker cube. The inner edges contrast defines one of two possible cube's orientations, left or right, and determines stimulus ambiguity. When ambiguity is low, cubes morphology is different for the left and right orientations. Therefore, subjects easily report the correct one. For the high ambiguity, stimulus morphology becomes similar for different orientations; therefore, subjects spent more effect to find the differences. In the recent works, we observed that subjects responded faster to the Necker cubes presentedat the end of the experiment [16]. We also found that the brain utilized different neural mechanisms when processing stimuli with low and high ambiguity [2; 4; 17]. Based on these results, we hypothesized that during a long experiment with the Necker cubes, the observer's state changed, causing changes in behavioral performance. We expected to find the neural correlates of these changes in the prestimulus state and use them to predict the performance of the ongoing stimulus. We also supposed that changes in the human condition had a different effect depending on the stimulus ambiguity. To test this hypothesis, we tracked the behavioral characteristics (decision times and errors) and simultaneously detected the EEG signals during a long monotonous task, including the Necker cubes interpretations. Behavioral monitoring revealed that decision time decreased with time on task, despite the ambiguity. For high ambiguity, we also observed a reduction of perceptual errors. EEG analysis showed growing prestimulus 9-11 Hz EEG power in the right temporal region. This EEG power negatively correlated with the decision time to the stimuli, with low ambiguity and the erroneous responses rate to stimuli with high ambiguity. The obtained results confirm that monitoring prestimulus EEG power enables predicting perceptual performance on the behavioral level.