A region-based two-step P300-based brain–computer interface for patients with amyotrophic lateral sclerosis

• We investigated the visual P300-based BCI performance of individuals with amyotrophic lateral sclerosis (ALS).
• We prepared two types of input procedures, the conventional row/column (RC) speller and the two-step speller, and evaluated their online performance.
• The two-step procedure provided significantly increased accuracy compared with a conventional RC speller for the ALS patients.

ObjectiveThe P300-based brain–computer interface (BCI) is designed to help patients with motor disabilities to control their environment, and it has been used successfully in patients with amyotrophic lateral sclerosis (ALS). However, some ALS patients were unable to use the visual P300-BCI with the conventional row/column presentation. In this study, we evaluated the effect of a newly developed region-based two-step P300 speller, which has a larger flashing area than the conventional visual array.MethodsSeven ALS patients and seven age- and sex-matched able-bodied control subjects were required to input hiragana characters using our P300 BCI system. We prepared two types of input procedures, the conventional row/column (RC) speller and the two-step speller, and evaluated their online performance.ResultsThe mean online accuracy of the ALS patients was 24% for the RC condition and 55% for the two-step condition. The accuracy of the control subjects was 71% and 83% for the RC and two-step condition, respectively. Accuracy in ALS patients was significantly lower than that in the control subjects, and the new visual stimuli significantly increased accuracy of ALS patients. Using the new speller, two ALS patients showed an initial accuracy sufficient for practical use (>70%). The other two ALS patients, who performed better in the first trial using the new speller, continued to experience the BCI system, and their mean accuracy increased to 92%.ConclusionsThe two-step procedure for the visual P300 BCI system provided significantly increased accuracy for ALS patients compared with a conventional RC speller.SignificanceThe new region-based two-step P300 speller was effective in ALS patients, and the system may be beneficial to expand their range of activities.