PolyMorph: A P300 Polymorphic Speller

P300 is an electric signal emitted by brain about 300 milliseconds after a rare, but relevant-for-the-user event. Even if it is hard to identify and it provides a low-rate communication channel, it can be used in cases in which other evoked potentials fail. One of the applications of this signal is a speller that enables subjects who lost the control of their motor pathways to communicate by selecting one by one each character of a sentence in a matrix containing all the alphabet symbols. This paper provides an improvement of this paradigm and it aims at reducing both the error rate and the time required to spell a sentence by exploiting the redundancy which is present in all the natural languages.