Figure 2. Example of the P300 BCI game Billiard Puzzle display.

Each “bouncing ball” contained a fragment of the picture being assembled on the right. The correct order of targets is cued by letters of the Russian alphabet. The current target is marked by a circle in the right panel. The ball with the letter “B” is flashing here. A counter at the bottom right indicates the number of errors (here, four errors). Note that this display follows the scheme presented in Figure 1 D (moving stimulus positions and single-cell presentation mode).