Spatial Attention Effects on P300 BCI Performance: ERP and Eye-Tracking Study

P300 brain–computer interface (BCI), based on P300 (or P3) event-related potential component, is one of the first BCIs and has various applications, one of which is text typing. This study was conducted to examine visual spatial attention, eye gaze, and event-related potential in a P300 BCI speller. 24 healthy volunteers (7 males) participated in the study, and their electroencephalogram and eye movements were recorded in three different experimental conditions: overt attention, covert attention, and gaze fixation. Results showed that performance was significantly lower in the covert attention condition (5% median accuracy compared to 90% with overt attention). Gaze fixation without allocation of attention yielded an 80% accuracy, despite higher gaze dispersion and lower average gaze duration for fixation characters. Event-related potentials analysis revealed that covert attention led to smaller N1 and P2 components, as well as a later and smaller P3 component. Our findings emphasize the importance of gaze fixation for the performance of classic P300 BCI spellers and suggest gaze shifts as the main source of spelling errors. This information can also be used to design high-performance covert attention BCIs that focus on the P3 in the absence of early exogenous components.