Usability of the P300 Speller: Towards a More Sustainable Brain-Computer Interface

To provide additional empirical evidence on the usability of a P300-based BCI system, P300 Speller, this study assessed how the matrix layout of the P300 Speller interface and inter-stimulus interval (ISI) affect task performance (accuracy, amplitude, latency, and information transfer rate) and user preference. Twenty-two able-bodied participants underwent a 2 (62.5 vs. 312.5 milliseconds ISI) by 3 (6 x 6, 4 x 9, and 3 x 12 matrix layout) within-subjects design experiment, in which participants were asked to type 10-character words by focusing on a character that they want to spell. The overall accuracy in the present study was 85.5%. A shorter ISI yielded higher information transfer rates while a longer ISI produced higher amplitudes. Matrix layout significantly affected information transfer rates. Participants had no significant preferences over the usage conditions. These results should provide firm, empirical evidence concerning BCI system usability, which can help understand BCI usersʹ experiences and uncover potential problems that may cause their experiences to be unpleasant or difficult.