Brain–Computer Interfaces - Index of

92 G. Pfurtscheller et al.
Fig. 8 Photographs of the experimental setup and demonstration at the Wired Nextfest 2007
needed to undergo cue-based training (CFR1) and gain satisfying self-paced control
(CFR1 and CFR2) was about 6 h.
7 Future Aspects
There are a number of concepts and/or ideas to improve BCI performance or to
use other input signals. Two of these concepts will be discussed shortly. One is to
incorporate the heart rate changes in the BCI, the other is to realize an optical BCI.
A hybrid BCI is a system that combines and processes signals from the brain
(e. g., EEG, MEG, BOLD, hemoglobin changes) with other signals [70, 71]. The
heart rate (HR) is an example of such a signal. It is easy to record and analyze and
it is strongly modulated by brain activity. It is well known that the HR is not only
modified by brisk respiration [59], but also by preparation of a self-paced movement
and by MI [8, 43]. This mentally induced HR change can precede the transient
change of EEG activity and can be detectable in single trials as shown recently in
[41].
Most BCIs measure brain activity via electrical means. However, metabolic
parameters can also be used as input signals for a BCI. Such metabolic parameters
are either the BOLD signal obtained with fMRI or the (de)oxyhemoglobin signal
obtained with the near-infrared spectroscopy (NIRS). With both signals a BCI has
been already realized [67, 3]. The advantage of the NIRS method is that a low-cost
BCI can be realized suitable for home application.
First results obtained with one- and multichannel NIRS system indicate that
“mental arithmetic” gives a very stable (de)oxyhemoglobin pattern [1, 72] (Fig. 9).
At this time, the classification of single patterns still exhibits many false positives.
One reason for this is the interference between the hemodynamic response and the
spontaneous blood pressure waves of third order known as Mayer-Traube-Hering
(MTH) waves [5]. Both phenomena have a duration of approximately 10 s and are
therefore in the same frequency range.