applications

Several recent BCI spelling systems are based on different EEG signals, including the mu rhythm22, 26 and the P300.31 The Mu rhythm systems made use of machine-learning paradigms that minimized training, with users of both mu-based systems reportedly averaging between 2. 3–7 characters/ minute22 and 2. 85–3. 38 characters/ minute. 26 The P300 system averaged 3. 66 selections/minute. 31 Townsend et al. 24 noted the reported rate depends on how the figure is computed, but study authors do not always provide details. Omitting time between trials increased Townsend et al. 31 results from 3. 66 to 5. 92 characters/second. In any case, these systems perform within a similar general range. At current BCI character rates, only users with limited options could benefi.

BCI systems have also been developed for control applications; for example, several groups have shown that human subjects can use their EEG activity to drive a simulated wheelchair. 10, 14 Bell et al. 1 showed the P300 could be used to select among complex commands to a partially autonomous humanoid robot; for a review of the use of BCI for robotic and prosthetic devices see McFarland and Wolpaw. 19

Several commercial concerns recently produced inexpensive devices purported to measure EEG. Both Emo-tiv and Neurosky developed products with a limited number of electrodes that do not use conventional gel-based recording technology27 and are intended to provide input for video games. Not clear is the extent to which they use actual EEG activity, as opposed to scalp-muscle activity or other non-brain signals. Given the well-established prominence of EMG activity in activity recorded from the head, it seems likely that such signals account for much of the control these devices provide. 27

Conclusion

In a review of the use of BCI technology for robotic and prosthetic devices, McFarland and Wolpaw19 concluded that the major problem facing BCI applications is how to provide fast, accurate, reliable control signals, as well as other uses of BCIs. Current BCI systems that operate using actual brain activity can provide communication-and-control

sensorimotor
rhythm-based
BCIs may provide
several advantages
over systems
that depend on
complex cognitive
operations.

options of practical value mainly for people severely limited in their motor skills and thus have few other options. Widespread use of BCI technology by individuals with little or no disability is unlikely in the short-term and would require much greater speed and accuracy than has so far been demonstrated in the scientific literature.

Noninvasive and invasive methods would both benefit from improved recording methods. Current invasive methods do not deal adequately with the need for long-term performance stability. The brain’s complex reaction to an implant is still imperfectly understood and might impair long-term performance. Noninvasive EEG electrodes require some level of skill in the person placing them, as well as in periodic maintenance to ensure sufficiently good contact with the skin; more convenient and stable electrodes are under development. Improved methods for extracting key EEG features and translating them into device control, as well as user training, would also help improve BCI performance.

Recent developments in computer hardware provide compact portable systems that are extremely powerful. Use of digital electronics has also led to improved size and performance of EEG amplifiers. Thus it is no longer necessary to use a large time-shared mainframe, as it was with Vidal34; standard laptops easily handle the vast majority of real-time BCI protocols. Signal-processing and machine-learning algorithms have also been improved. Coupled with discovery of new EEG features for BCI use and development of new paradigms for user training, such improvements are gradually increasing the speed and reliability of BCI communication and control, developments facilitated by the BCI2000 software platform. 25

BCI2000 is a general-purpose re-search-and-development system incorporating any brain signal, signal-processing method, output device, and operating protocol. BCI2000 consists of a general standard for creating interchangeable modules designed according to object-oriented principles (see Figure 4), including a source module for signal acquisition, signal-processing module, and user-application module. Configuration