Positive Technology Journal

A P300 event-related potential brain-computer interface (BCI): The effects of matrix size and inter stimulus interval on performance.

Biol Psychol. 2006 Jul 21;

Authors: Sellers EW, Krusienski DJ, McFarland DJ, Vaughan TM, Wolpaw JR

We describe a study designed to assess properties of a P300 brain-computer interface (BCI). The BCI presents the user with a matrix containing letters and numbers. The user attends to a character to be communicated and the rows and columns of the matrix briefly intensify. Each time the attended character is intensified it serves as a rare event in an oddball sequence and it elicits a P300 response. The BCI works by detecting which character elicited a P300 response. We manipulated the size of the character matrix (either 3x3 or 6x6) and the duration of the inter stimulus interval (ISI) between intensifications (either 175 or 350ms). Online accuracy was highest for the 3x3 matrix 175-ms ISI condition, while bit rate was highest for the 6x6 matrix 175-ms ISI condition. Average accuracy in the best condition for each subject was 88%. P300 amplitude was significantly greater for the attended stimulus and for the 6x6 matrix. This work demonstrates that matrix size and ISI are important variables to consider when optimizing a BCI system for individual users and that a P300-BCI can be used for effective communication.