Brain--computer interface (BCI): is it strictly necessary to use random sequences in visual spellers?

The P300 speller is a standard paradigm for brain--computer interfacing (BCI) based on electroencephalography (EEG). It exploits the fact that the user's selective attention to a target stimulus among a random sequence of stimuli enhances the magnitude of the P300 evoked potential. The present study questions the necessity of using random sequences of stimulation. In two types of experimental runs, subjects attended to a target stimulus while the stimuli, four in total, were each intensified twelve times, in either random order or deterministic order. The 32-channel EEG data were analyzed offline using linear discriminant analysis (LDA). Similar classification accuracies of 95.3% and 93.2% were obtained for the random and deterministic runs, respectively, using the data associated with 3 sequences of stimulation. Furthermore, using a montage of 5 posterior electrodes, the two paradigms attained identical accuracy of 92.4%. These results suggest that: (a) the use of random sequences is not necessary for effective BCI performance; and (b) deterministic sequences can be used in some BCI speller applications.

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