Figure 1.

(A) Spelling system used by the patient in a partner scanning approach. Characters are grouped into four categories to increase spelling speed. (B) We developed a BCI system based on the partner scanning approach described in (A). Four tactile stimulation units were placed on the patient's left arm. We individually adjusted the BCI paradigm to the partner scanning approach the patient is used to. Each tactor either represented one of the groups of characters, or represented a character of one prior selected group. Please note that we restricted the number of tactors to four, thus limiting the possible selections. Practical use of the system would require seven tactors (up to six tactors for selection of characters plus one tactor to undo a wrong selection).