BCIs are a direct communication pathway between the brain and external devices. eeG measurements at the Danish master’s program in medicine & technology; http://www.medicin-ing.dk/kandidat/en.

PHo To Gra PH By lar S BaHl

EEG research reflects two major paradigms: evoked potentials and oscillatory features. Evoked potentials are transient waveforms, or brief perturbations in the ongoing activity, that are phase-locked to an event (such as a visual stimulus). They are typically analyzed by averaging many similar events in the time-domain. Although oscillatory features in an EEG may occur in response to specific events, they are usually not phase-locked and typically studied through spectral analysis. Historically, most EEG studies have examined phase-locked evoked potentials. Both these major paradigms have been applied in BCIs. 36

The term “brain-computer interface” can be traced to Jacques Vidal of the University of California, Los Angeles who devised a BCI system in the

1970s based on visual evoked-poten-
tials. 34 His users viewed a diamond-
shape red checkerboard illuminated
with a xenon flash. By attending to dif-
ferent corners of the flashing checker-
board, they could generate right, up,
left, and down commands, enabling
them to move through a maze present-
ed on a graphics terminal. An IBM360
mainframe digitized the data, and
an XDS Sigma 7 computer controlled
the experimental events. Users first
provided data to train a stepwise lin-
ear discriminant function, then navi-
gated the maze online in real time.
Thus, Vidal34 used signal-processing
techniques to realize real-time analy-
sis of the EEG with minimal averag-
ing. The waveforms showed by Vidal34
suggested his BCI used EEG activity in
the timeframe of the N100-P200 com-
ponents, with the N and P indicating
negative and positive peaks, and the
numbers indicating the approximate
latency in msec.