Evolution of errors performed over time ( trials) by the unsupervised method for the three unsupervised blocks.

<p>Time is on the horizontal axis, while the lines represent users. The order of the users equals that of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102504#pone-0102504-g004" target="_blank">Fig. 4</a>, with represented by the top line and by the bottom line. For each trial and user, a green square indicates an accurate selection, a black one marks an error. Clearly, the unsupervised classifier commits most erroneous decisions shortly after its random initialization at the beginning of each novel block. In the majority of cases users were able to effectively control the BCI by the end of a block.