BCI - controllable eeg-signals

P300 is the name of an electrical peak of about 300ms in lenghth. It occurs in the EEG when recorded over the so called parietal cortex, an area on both sides of the brain roughly some centimeters above the ears. The p300 peak is an unconscious reaction on significant or unusual auditory, visual or tactile stimuli.
To use it for a BCI, users face a matrix with numbers or letters, say 6x6. These rows or columns flash one after the other at a rate of about eight times a second. The user has to count how often the desired letter or number is illuminated, and doing so, he unconsciously produces p300 peaks (kind of an electrical "ahhhhhh"...), which the software averages to find out the user's intent (see illustration).
P300-based BCIs have a number of technical and practical advantages (more) and are likely to be considerably faster than the SCP-systems, but there has not yet been enough practical experience with them to give a final judgement.

P300-waves are shorter than SCPs and thus potentially faster when it comes to information gathering and bit rate. It has been estimated that, with a suitable language device, current systems could produce about one word a minute, with an increase mainly a question of technology.

The most striking advantage of p300-BCIs is that they do not require training, as a p300 is a subconscious reaction on sensory stimuli. The downside of this is that p300 might be subject to habituation, i.e. its quality might fall over time. But the experience with p300- and related systems has not been long enough, yet.

Furthermore, it must be added, that it seems to be still an open argument if p300 potentials are really independent from any motor activity, especially eye movement. If not, there might be difficulties in using a p300-BCI for severely handicapped.

Advantages of the p300-approach

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