A BCI system measures particular components or features of EEG activity and uses the results as a control signal.Some systems use evoked potentials, which are EEG
components produced by stereotyped sensory stimuli.For example, Farwell and Donchin (1988) and Sutter(1992) used visual-evoked potentials. Other systems, including
our own, use EEG components that are spontaneous in the sense that they are not strongly linked to specific sensory inputs. Our system uses the mu rhythm, an 8-12 Hz rhythm recorded from the scalp over somatosensory cortex and/or closely related higher frequency
components