Brain–Computer Interfaces - Index of

90 G. Pfurtscheller et al.
In this experiment, the 33-year-old tetraplegic patient was trained to induce beta
oscillation during foot MI (see Section 3.2). The participant sat in his wheelchair
in the middle of a multi-projection based stereo and head-tracked VR system commonly
known as CAVE (computer animated virtual environment, [4]), in a virtual
street with shops on both sides and populated with 15 avatars, which were lined up
along the street [10, 23](seeFig.7). The task of the participant was to “move” from
avatar to avatar towards the end of the virtual street by movement imagination of
his paralyzed feet. From the bipolarly recorded single EEG channel the band power
(15–19 Hz) was estimated online and used for control. The subject only moved forward
when foot MI was detected – that is, when band power exceeded the threshold
(see Fig. 7).
On 2 days, the tetraplegic subject performed ten runs, and was able to stop at
90 % of the 150 avatars and talk to them. He achieved a performance of 100 % in
four runs. In the example given in Fig. 7, the subject correctly stopped at the first
3 avatars, but missed the fourth one. In some runs, the subject started earlier with
foot MI and walked straight to the avatar, whereby in other runs, stops between the
avatars occurred. Foot MI could be detected during 18.2 % ± 6.4 % of the run time.
The averaged duration of MI periods was 1.6 s ± 1.1 s (see [22]).
This was the first work that showed that a tetraplegic subject, sitting in a
wheelchair, could control his movements in a virtual environment using a self-paced
filtered EEG
15-19Hz [µV]
logBP [µV^2]
go/
stop
threshold
My name
is Maggie!
Avatar
walked
away.
avatar starts speaking and walks away
communication
range
time [s]
Fig. 7 Picture sequence before, during and after the contact with an avatar (upper panel). Example
of a band-pass filtered (15–19 Hz) EEG, logarithmic band power time course with threshold (Th)
and go/stop signal used for VE control (lower panels) (modified from [21])