The Hybrid BCI

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 post-imagery 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).