Robust visual stimulator for P300-BCI

A method of displaying robust visual stimulator for P300-BCI is proposed. This visual stimulator plays vital role in BCI system since the evoked potential with duration of 300 ms is mainly affected by the precise timing of each trial. It is preferable that the number of trials must be set as small as possible and it means that the stimulator which provides the random stimuli must operate in the very exact time. There are three main factors which contribute to the robustness of P300 visual stimulator in this paper: accurate timing provided by the high resolution system timer, video graphic display technology (i.e. OpenGL in this paper), and process/thread priority management. From the measurement, it can be seen that the timing function which is provided through a dedicated thread, has a very high accuracy with signal delay less than 300 ¿s. All of programs written in this paper were developed using Open Source software tools. It is developed with two kind of patterns: letter matrix and icon matrix. It also contains two stimulation method: random block of row/column and random cells, by which it may increase cell´s uncertainty and finally enhance P300 amplitude.