E.A., Gates, G.R. (1990) Comparisons of the nonlinear dynamics of electroencephalograms under various task loading conditions: a preliminary report. Biol Psychol 31:173-191 Grimmett, G. (1989) Percolation. Springer-Verlag. Guckenheimer, J., Holmes, P. (1983): Nonlinear Oscillations, Dynamical Systems and Bif