We have studied the screening tool for dementia patients using a P300-based spelling-BCI to develop a new cognitive function evaluation method. We quantified a low attention with dementia using the average distance from the incorrect characters to the correct characters on the Japanese alphabet screen. We called the character distance to Spelling-Error Distance Value (SEDV). We conducted experiments for 24 elderly subjects, and performed regression analysis between SEDV and neuropsychological testing (MMSE, FAB, TMT and DST). As the results, there was a significant negative correlation between MMSE and SEDV (r = −0.41, p < 0.05), and there was a significant negative correlation between FAB and SEDV (r = −0.65, p < 0.001). Next, 24 subjects divided into five groups according to the MMSE scores. There was a difference of SEDV 2.58 characters between MMSE average of 10.5 point group and MMSE average score of 27.6 point group, 2.89 characters between the 10.5 point group and the 24.9 point group. Therefore, SEDV could be an index of the low attention with dementia in the limited MMSE average group. In addition, because of significant negative correlation between FAB and SEDV in less than 24 point of MMSE (r = −0.95, p < 0.05), SEDV could be an index of frontal lobe function deterioration limitedly.
