[Eeglablist] "Subtract individual subject mean spectrum"——why the line charts of two groups are mirror inverted

[杨璐娜]

Hello,

I'm trying to use the EEGLAB 14_1_2b STUDY set to plot spectra of 2 groups with the same number of subjects. 
After selecting "Subtract individual subject mean spectrum" option, the line of the first group and the line of the second group are mirrored in opposite directions along y=0. 
But in order to compare the differences between the two groups, I need them to be in the same direction. And when this option is not selected, the two groups are in the same direction. 
I looked in the manual but I think its not mentioned there. So, can anyone explain me why this option caused this kind of problem? And is there any way to change this situation?

I would like to express my most sincere gratitude to the great support if you can help me!

Luna Y