The joint use of the tangential electric field and surface Laplacian in   EEG classification
  This paper discusses the use of the scalp electric field to decode EEG-recorded brain processes. Instead of using bipolar measurements, the scalp electric field is described as a 3-vector field whose orthogonal components are obtained from the data through spline differentiation. The method was tested in the context of brainwave recognition with experiments involving brain representation of spoken phonemes, visual images, and mental images. The practical effect of improvements in recognition rates was assessed by estimating effect sizes and confidence intervals, the results suggesting a good prospect for other applications. 
C. G. Carvalhaes and J. Acacio de Barros and M. Perreau-Guimar\~aes   and P. Suppes
q-bio.NC physics.med-ph