Single-paradigm and hybrid brain computing interfaces and their use by disabled patients

Brain computer interfacing (BCI) has enjoyed increasing interest not only from research communities such as engineering and neuroscience but also from visionaries that predict it will change the way we will interact with technology. Since BCIs establish an alternative communication channel between the brain and the outside world, they have been hailed to provide solutions for patients suffering from severe motor- and/or communication disabilities such as fully paralyzed locked-in syndrome patients. However, despite single-case successes, which sometimes reach a broad audience, BCIs are actually not routinely used to support patients in their daily life activities. This review focusses on non-invasive BCIs, introduces the main paradigms and applications, and shows how the technology has improved over recent years. We identify patient groups that potentially can benefit from BCIs by referring to disability levels and etiology. We list the requirements, indicate how BCIs can tap into their spared competences, and discuss performance issues also in view of other assistive communication technologies. We discuss hybrid BCIs, a more recent development that combines paradigms and signals, possibly also of non-brain origin, to increase performance in terms of accuracy and/or communication speed, also as a way to counter the low performance with a given paradigm by involving another, more suitable one (BCI illiteracy). Finally, we list a few hybrid BCI solutions for patients and note that demonstrations with the ones based entirely on brain activity are still scarce.