Are current gait-related artifact removal techniques useful for low-complexity BCIs?

A recent study has shown that several gait-related artifact removal techniques are not helpful to improve the performances of an ultra-compact P300-based BCI system integrating only three electrodes and designed for out of the lab experiments. Moreover, the authors advise to use seven electrodes with a standard xDawn spatial filter - known to magnify the P300 response - in order to obtain the best performance/compactedness ratio. However, the positive impact of the xDawn filter and the gaitrelated artifact removal techniques on the BCI performance with seven EEG electrodes had not been precisely evaluated at that time. This is precisely what we do in this study using seven healthy subjects walking at three different speeds. Astonishingly, none of the methods, even the so-called xDawn spatial filter, does significantly outperform the raw data. Thereby, the recommendation considering a low-complexity four-state P300 BCI under ambulatory conditions would be to use filtered raw data without specific gait-related artifact removal techniques.