ERP-based Speller with a New Paradigm

In most implementation of an ERP-based speller, standard row-column paradigm (RCP) was used. However, RCP is susceptible to adjacency-distraction errors because items in the same row or column of the target flash at the time of a half when the target item flashes. The adjacency-distraction errors could be reduced if the number of flanking items that flash with the target is diminished. This study presents a novel P300-based stimulus presentation called row-column-diagonal paradigm (RCDP) where characters on the main diagonal and the anti-diagonal in the matrix flash in addition to characters on the row and columns. In RCDP, items in the same row, column, main diagonal, and anti-diagonal of the target flashes at the time of a quarter when the target item flashes. Using a 6×6 matrix of alphanumeric characters and keyboard commands, ten college students used RCP and RCDP. Stepwise linear discriminant analysis (SWLDA) for the EEG signals recorded in calibration phases was used to calculate discrimininant function. By applying the discrimininant function to electroencephalography (EEG) signal recorded in the test phase, the probability whether the item was the target or not was evaluated. Average accuracy was 76.6% in RCP while 84.0% in RCDP. With RCP, most errors were occurred in the same row or column of the target; on the other hand, with RCDP in the same row, column, main diagonal, or anti-diagonal of the target. These findings indicate how RCDP reduces adjacency-distraction errors and might be able to contribute to develop more advanced stimulus presentation paradigm.