*2.3. Experimental Protocol*

The participants were informed about the experimental protocol beforehand in addition to the corresponding textual directives on the screen throughout the experiment. The experiment started with the presentation of a static (non-flickering) square image with a red dot at the center, on which the participant had to concentrate their gaze for 120 s. The recorded brain activity was used as a reference signal or background. After a short rest, the square image started flickering and was presented 2–5 times (depending on the subject) for 120 s, interrupted by a 30-s resting period between each presentation. The flickering stimulus was presented at least 3 times to all subjects except for subject "sub10". The starting times of the background and flickering recordings were marked with event triggers using a parallel-port setup.
