I. Outline
Brain machine interfaces use brain activities as commands, for which brain activities are usually measured by electroencephalogram (EEG). However, EEG is very sensitive to the other bio-signals: heart rate, eye movement, motion, and so on. Therefore, the use of BCI employing only EEG has limitations, so other bio-signal detection modalities are usually included as supplementary modalities, including those such as electrocardiogram (ECG), electromyography (EMG), photoplethysmography (PPG), electrooculogram (EOG), and galvanic skin reflex (GSR) [1]–[4]. However, while brain activities cannot be directly measured by such modalities, they can be directly measured by the use of functional near-infrared spectroscopy (fNIRS) through hemodynamic responses.