Fig. 7

Correlation between early frontal negativity (EFN) and middle frontal negativity (MFN) for the happy (HAP) faces. Correlation matrix (left part) was filtered by an α level of p < 0.05. Gradual red areas represent intervals for significant correlations in permutation correlation analyses. EFN (65–85 ms) positively correlated with MFN (175–195 ms) (see for summary, a right upper scatter diagram). Actual coefficient (r = 0.500) is outside the 95 % confidence interval (gray area) of 10,000 dummy coefficients (a right lower histogram). The asterisk indicates statistical significance of p < 0.05