Possible Sources of Perceptual Errors in P300-based Speller Paradigm

INTRODUCTION Our ability of detecting or identifying stimuli is limited and we are susceptible to different kinds of illusions or ‘mistakes’. Perceptual limits are often investigated by using rapid serial visual presentation (RSVP) experiments. In a typical RSVP experiment stimuli are sequentially presented at a rate of 6 to 20 items per second and observers are asked to detect or identify a target that differs (e.g., in colour or shape) from nontarget stimuli. In RSVP target identification is normally quite accurate, but there can be “intrusion” effects by which the target appears to acquire non-target features. Within independent BCI [2], P300 potentials have provided a means of detecting user’s intentions concerning the choice of objects within a visual field: an area pioneered by Farwell and Donchin [1] who developed a protocol whereby a subject is shown a characters’ matrix the rows and columns of which flash randomly at high speed. Large P300 waves are observed in response to the flashing of the chosen character.