Gaze-independent BCI spellers based on covert attention and feature attention

One of the foremost goals of rehabilitative Brain-Computer Interface (BCI) research is to design a mental typewriter, that enables paralyzed patients to communicate with their environment based on their brain activity. For the most popular candidate, the so called Matrix Speller, a recent study has shown that the spelling accuracy completely breaks down when the user is not allowed to fixate the target symbol by gaze but rather a central fixation point. This observation raises the need for BCI spellers that work effectively also for patients who have lost the ability to shift their gaze to a required position. Here we will present three variants of visual spellers that are based on covert spatial attention and on non-spatial feature attention. The results of our study with 13 healthy participants impressively demonstrate that these spellers obtain a similar spelling performance during center fixation as the orignal Matrix Speller with target fixation.