Brain computer interface: the use of low resolution surface Laplacian and linear classifiers for the recognition of imagined hand movements

An EEG-based Brain Computer Interfaces (BCIs) require on-line detection of mental states from spontaneous or surface Laplacian (SL) transformed EEG signals. However, accurate SL estimates require the use of many EEG electrodes, when local estimation methods are used. Since BCI devices have to use a limited number of electrodes for practical reasons, we investigated the performances of spline methods for SL estimates using a limited number of electrodes (low resolution SL). In this paper, recognition of mental activity was attempted on both raw and SL-transformed EEG data from five healthy people performing two mental tasks, namely imagined right and left hand movements. Linear classifiers were used including Signal Space Projection (SSP) and Fisher´s linear discriminant. Results showed an acceptable average correlation between the waveforms obtained with the low resolution SL and those obtained with the SL computed from 26 electrodes (full resolution SL). Recognition scores for mental EEG-patterns were obtained with the low-resolution surface Laplacian transformation of the recorded potentials when compared with those obtained by using full resolution SL (82%).