“…However, it is still needed to improve the usability of these BCI speller systems. Some factors, such as the mental fatigue induced by a long use (Kececi et al, 2006;Murata and Uetake, 2001), the sustained attention at a symbol on screen (Mangun and Buck, 1998), the user motivation (Kececi et al, 2006;Kleih et al, 2010) or his/her frustration due to a mistake (Kleih et al, in press) can influence the amplitude and latency of the P300 component (See Polich and Kok, 1995, for a review). In this regard, the influence on performance of the temporal and spatial aspects of the user interfaces of these systems is increasingly drawing the attention of researchers (Lu et al, 2013;McFarland et al, 2011;Shih et al, in press) This paper presents a study aimed at contributing to this line of research.…”