Brain–Computer Interfaces - Index of

234 J.E. Huggins
Fig. 5 ECoG detection and
fMRI activation for a subject
performing palmar pinch.
Electrode location color
indicates average
HF-difference. Green regions
were active on fMRI
Brain–Computer Interface” by Miller and Ojemann in this volume describes this
work in detail, so only a brief description is given here. Working with epilepsy
surgery patients over a 3–8 day period, Leuthardt et al. demonstrated the first BCI
operation of cursor control using ECoG. Sensorimotor rhythms in ECoG related to
specific motor tasks and motor imagery were mapped in real-time to configure the
BCI. With a series of feedback sessions, four subjects were then trained to perform
ECoG-based cursor control [4, 41]. Subjects controlled the vertical cursor speed
while automatic horizontal movement limited trial duration to 2.1–6.8 s. Subjects
were successful at a binary selection task in 74–100% of trials. This work showed
that ECoG sensorimotor rhythms in the mu (8–12 Hz), beta (18–26 Hz), and gamma
(> 30 Hz) frequency ranges could be used for cursor control after minimal training
(in comparison with that required for EEG). This group has also shown that ECoG
can be used to track the trajectory of arm movements [4, 42].
6.2.4 University of Wisconsin – Madison
Williams and Garrell at the University of Wisconsin have also started ECoG experiments
using BCI2000 [7, 17] that used both auditory and motor imagery tasks for
real-time cursor control to hit multiple targets. Subjects participate in 2–7 training
sessions of 45 min in duration. Subjects first participate in a screening session
during which they perform different auditory and motor imagery tasks which are
analyzed off-line to identify tasks and electrodes with significantly different frequency
components compared to a rest condition. These electrodes are then utilized
in the on-line feedback experiments. Subjects control the vertical position of a cursor
moving across the screen at a fixed rate, but the duration of a trial is not reported.
Subjects attempt to guide the cursor to hit one of 2, 3, 4, 6, or 8 targets. Subjects
were able to achieve significant accuracy in only a few sessions with typical performance
on the 2-target task of about 70% of trials [17]. One subject achieved 100%
accuracy at a 3 target task, and the same subject had 80, 69 and 84% accuracy on
the 4, 6, and 8 target tasks respectively [17].