Alphabet matrix layout in P300 speller may alter its performance

The P300 speller is one of the brain-computer interfaces that uses the P300 event-related potential. The performance of the P300 speller is influenced by various parameters related to the matrix displayed. In addition, it is reported that letters in the corner or at the edge of the matrix can be concentrated on more easily, giving a higher accuracy rate for the P300 speller. In order to improve the performance of the P300 speller, we have focused on an alphabet layout on the matrix and evaluated P300 amplitude and system output in terms of inter-character distance. Experimental results revealed that the shorter the inter-character distance, the larger the P300 amplitude. However, this did not lead to better system performance. The results suggest that a classifier in the system should be improved to make good use of the characteristics of P300 amplitude observed in the experiment.