BNCI 2014-004 Motor Imagery dataset. (Dataset B from BCI Competition 2008.)

This data set consists of EEG data from 9 subjects of a study published in
[1]_. The subjects were right-handed, had normal or corrected-to-normal
vision and were paid for participating in the experiments.
All volunteers were sitting in an armchair, watching a flat screen monitor
placed approximately 1 m away at eye level. For each subject 5 sessions
are provided, whereby the first two sessions contain training data without
feedback (screening), and the last three sessions were recorded with
feedback.

Three bipolar recordings (C3, Cz, and C4) were recorded with a sampling
frequency of 250 Hz.They were bandpass- filtered between 0.5 Hz and 100 Hz,
and a notch filter at 50 Hz was enabled.  The placement of the three
bipolar recordings (large or small distances, more anterior or posterior)
were slightly different for each subject (for more details see [1]).
The electrode position Fz served as EEG ground. In addition to the EEG
channels, the electrooculogram (EOG) was recorded with three monopolar
electrodes.

The cue-based screening paradigm consisted of two classes,
namely the motor imagery (MI) of left hand (class 1) and right hand
(class 2).
Each subject participated in two screening sessions without feedback
recorded on two different days within two weeks.
Each session consisted of six runs with ten trials each and two classes of
imagery.  This resulted in 20 trials per run and 120 trials per session.
Data of 120 repetitions of each MI class were available for each person in
total.  Prior to the first motor im- agery training the subject executed
and imagined different movements for each body part and selected the one
which they could imagine best (e. g., squeezing a ball or pulling a brake).

Each trial started with a fixation cross and an additional short acoustic
warning tone (1 kHz, 70 ms).  Some seconds later a visual cue was presented
for 1.25 seconds.  Afterwards the subjects had to imagine the corresponding
hand movement over a period of 4 seconds.  Each trial was followed by a
short break of at least 1.5 seconds.  A randomized time of up to 1 second
was added to the break to avoid adaptation

For the three online feedback sessions four runs with smiley feedback
were recorded, whereby each run consisted of twenty trials for each type of
motor imagery.  At the beginning of each trial (second 0) the feedback (a
gray smiley) was centered on the screen.  At second 2, a short warning beep
(1 kHz, 70 ms) was given. The cue was presented from second 3 to 7.5. At
second 7.5 the screen went blank and a random interval between 1.0 and 2.0
seconds was added to the trial.