Brain–Computer Interfaces - Index of

256 K.J. Miller and J.G. Ojemann
areas are becoming more pronounced), and the overall scale (to the top right) is
increasing. Similar one dimensional tasks were performed for tongue and hand. The
hand movement was coupled to left-right cursor movement, in preparation for the
combination of the two into a two dimensional task.
Figure 7c, Two-Dimensional Cursor Feedback: In the last stage of the experiment,
two one dimensional control signals are combined into a single cursor to
target task. If the two signals are independent, as is the case here, then the transition
between robust control in two one-dimensional tasks and robust control in
one two-dimensional task is straightforward. The combination of hand and tongue
linked features is good (as in (c)), because they are well demarcated on the precentral
gyrus, but the pair chosen in any particular instance will be dependent on
the coverage of the electrode array. The example shown in (c), with the frequency
range 80–90 Hz demonstrates how robust, screened, features (left) can be used for
robust control in one-dimensional tasks (center). The electrode for up-down control
in both the one- and two-dimensional tasks was from the classic tongue area. The
electrode for left-right control in both the one- and two-dimensional tasks was from
the classic hand area. The one- and two-dimensional control tasks were successful
(100% Left/Right 1D, 97% Up/Down 1D, and 84% 2D).
7 Conclusion
ECoG provides robust signals that can be used in a BCI system. Using different
kinds of motor imagery, subjects can volitionally control the cortical spectrum in
multiple brain areas simultaneously. The experimenter can identify salient brain
areas and spectral ranges using a cue based screening task. These different kinds
of imagery can be coupled to the movement of a cursor on a screen in a feedback
process. By coupling them first separately, and later in concert, the subject can learn
to control multiple degrees of freedom simultaneously in a cursor based task.
Acknowledgements Special thanks to Gerwin Schalk for his consistent availability and insight.
The patients and staff at Harborview Medical Center contributed invaluably of their time and
enthusiasm. Author support includes NSF 0130705 and NIH NS07144.
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