Characteristics of event-related potentials in response to symbolical and alphabetical stimulation matrices used in a P300-based brain-computer interface

Abstract

In order to create a P300-based brain-computer interface (BCI) (the so-called Farwell-Donchin paradigm, FD) with a symbol matrix used as a stimulus, we compared characteristics of event-related potentials (ERPs) in response to stimulation by 6 × 6 matrices composed of either pictogram symbols or Cyrillic alphabet characters. Nine healthy adults were examined in 18 experiments, during which 28-channel EEGs were recorded in the course of stimulation with matrices of these two types. The obtained ERP data, i.e., amplitudes and peak latencies of the ERP components N1, P3 (with the P3a and P3b sub-components), and N4 were compared and analyzed for different types of stimulation matrices. In at least seven out of nine subjects, P3a, P3b, and N4 ERP amplitudes were larger in response to the symbol matrix than to the character matrix, while N1 amplitudes were larger for the character matrix. For N1 and P3a, the ERP latencies were shorter for the symbol matrix, while for P3b and N4, they were longer for the character matrix. The topography of differential ERP responses to the two types of stimuli was analyzed using a series of paired t-tests. Differences of ERP component amplitudes were determined individually for each of the 28 channels; next, for each site, absolute t-test values were summed for all nine subjects. For all ERP components studied, the t-test for peak amplitudes in response to target and non-target letters identified two separate areas with distinct lateralization. ERP responses to target and non-target symbols differed most in transversely extended areas. Finally, the yield surface of differential response to target letters and target symbols had a complex topography.