BNCI 2014-002 Motor Imagery dataset (BCI Competition 4 IIa)

This data set consists of EEG data from 9 subjects.  The cue-based BCI
paradigm consisted of four different motor imagery tasks, namely the imag-
ination of movement of the left hand (class 1), right hand (class 2), both
feet (class 3), and tongue (class 4).  Two sessions on different days were
recorded for each subject.  Each session is comprised of 6 runs separated
by short breaks.  One run consists of 48 trials (12 for each of the four
possible classes), yielding a total of 288 trials per session.

The subjects were sitting in a comfortable armchair in front of a computer
screen.  At the beginning of a trial ( t = 0 s), a fixation cross appeared
on the black screen.  In addition, a short acoustic warning tone was
presented.  After two seconds ( t = 2 s), a cue in the form of an arrow
pointing either to the left, right, down or up (corresponding to one of the
four classes left hand, right hand, foot or tongue) appeared and stayed on
the screen for 1.25 s.  This prompted the subjects to perform the desired
motor imagery task.  No feedback was provided.  The subjects were ask to
carry out the motor imagery task until the fixation cross disappeared from
the screen at t = 6 s.

Twenty-two Ag/AgCl electrodes (with inter-electrode distances of 3.5 cm)
were used to record the EEG; the montage is shown in Figure 3 left.  All
signals were recorded monopolarly with the left mastoid serving as
reference and the right mastoid as ground. The signals were sampled with.
250 Hz and bandpass-filtered between 0.5 Hz and 100 Hz. The sensitivity of
the amplifier was set to 100 μV . An additional 50 Hz notch filter was
enabled to suppress line noise

References
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[1] Tangermann, M., Müller, K.R., Aertsen, A., Birbaumer, N., Braun, C.,
       Brunner, C., Leeb, R., Mehring, C., Miller, K.J., Mueller-Putz, G.
       and Nolte, G., 2012. Review of the BCI competition IV.
       Frontiers in neuroscience, 6, p.55.