Berlin/Juli 2009

The hybrid BCI G. Pfurtscheller Institute for Knowledge Discovery, BCI-Lab, Graz University of Technology, Krenngasse 37, 8010 Graz, Austria

There are several different BCI approaches, which may or may not depend on external stimulation. Slow cortical potential (SCP)-, event-related desynchronisation (ERD)- and sensorimotor rhythm (SMR)-BCIs do not require external stimulation, while P300-BCIs and steady state visual evoked potential (SSVEP)-BCIs do. Dependent means in this respect that the user has to focus attention and/or gaze to flickering/flashing lights or and can therefore not completely freely decide to perform an action. Each type of BCI system has advantages and disadvantages. SSVEP-BCIs need minimal training time and can achieve a high information transfer rate (ITR), but have a relatively high false positive rate during rest. In contrast, an asynchronous brain switch based on the postimagery beta ERS has a low ITR, but can be set up quickly and easily with a low false position rate (Pfurtscheller and Solis-Escalante, Clin. Neurophysio. 2009). It is therefore a challenge to use the advantages of different BCI systems and create a “hybrid” BCI system by switching e.g. a battery of flickering lights (SSVEP-BCI) on or off by using a brain switch (ERD-BCI). Another type of “hybrid” BCI can analyse motor imagery related EEG changes and SSVEP amplitudes simultaneously. It was shown recently that such a “hybrid” strategy results in a better classification accuracy relative to either an ERD or SSVEP classification alone (Allison et al submitted 2009). Mental activity such as motor imagery activates cardiovascular nuclei in the brain stem, which modulates the heart rate (HR). Therefore, a “hybrid” BCI might also combine brain and non-brain signal, such as the HR, which could either be analysed and classified simultaneously or HR changes used to switch on or off a SSVEP-BCI (Scherer et al. JNE 2007) Last but not least, an optical BCI can also be used to switch an EEG-based BCI on or off. This combination can also be considered a “hybrid” BCI. “Hybrid” BCIs can therefore divided according to: The timing of the different mental tasks (subjects may perform the different tasks either simultaneously or sequentially); whether they combine different brain imaging approaches (EEG-based BCI and optical BCI); and whether they use only brain signals or combine signals from the brain and other physiological signals.