Fig. 1

Averaged HR and SCL over 2-h in EEG-vigilance stage. The line diagrams show the mean of heart rate (HR) and skin conductance level (SCL, z transformed) in corresponding EEG-vigilance stages in ignored (a) and attended (b) condition. To note, the values were calculated based on different subjects. The numbers of subjects in each stage are shown in parentheses. Error bars reflect standard error of the means. The asterisk and plus sign represent results of pared sample t tests, which asterisk means significant different between this stage and all other lower stages, while plus sign means some of the comparisons between this stage and other lower stages reached significance level. Each pared sample t test was only made for pairs with a sufficient sample size (n > 10), therefore the degree of freedoms were different for each pair. For more details please refer to the Table S2 (ignored condition) and Table S3 (attended condition) in Additional file 3