Fig. 6.

Ethanol reduces evidence for nonlinearity. To test whether ethanol produced an increase or a decrease in nonlinear structure in the EEG, we compared the evidence for nonlinearity under the placebo condition with that for the ethanol condition. This was accomplished by using a nonparametric rank test for each of the 8 sec segments of EEG for each subject and comparing, for each of the nonlinear measures, the values obtained from EEG with those from its surrogates for both the placebo and ethanol conditions. Then the number of segments for which a rank of 1 or 40 was obtained for the ethanol and placebo conditions was compared, using the Wilcoxon paired samples signed rank test. The placebo condition contained significantly more evidence for nonlinear structure, as measured by slope asymmetry (T = 90; p < 0.002), correlation dimension at embedding 4 (T = −106;p < 0.004), redundancy at embedding 4 and radius of 0.5 (T = 106; p < 0.004) and 1.0 (T = 125; p < 0.01), and redundancy at embedding 32 and radius of 1.5 (T= 115; p < 0.01). *p < 0.01; **p < 0.001.