[FieldTrip] Baseline Correction using 'relchange' or 'db'

mick.lehmann at uzh.ch mick.lehmann at uzh.ch
Wed Jul 29 15:55:38 CEST 2015

Dear Fieltrippers,

yesterday I addressed this mailing list with an issue regarding the baseline correction for time frequency analysis. While plotting a comparison of two conditions revealed exactly the results I've expected, the statistic didn't at all. Regardless of electrode, time window and freq range, the comparison of the two conditions was significantly different (with t-values between 8 and 10 and p < 0.001). Digging a little deeper, the main difference between the script for plotting and the one for stat analysis is that in for the figure, I've to indicate again the baselinewindow and the baselinetype:

diff = gaTF_Cond1;
diff.powspctrm = (gaTF_Cond1.powspctrm - gaTF_Cond2.powspctrm);

cfg = [];
cfg.baseline     = [-1 -.1];
cfg.baselinetype = 'db';  
cfg.maskstyle    = 'saturation';
cfg.zlim         = [-3 3];	
cfg.ylim         = [2 25];   
cfg.xlim         = [-1 2]; 
cfg.channel       = {'all'};
cfg.layout = 'C:\Users\MickLehmann\Documents\Emo_React_EEG\FieldTrip\Scripts\egi128_GSN_HydroCel3.sfp';
cfg.interactive = 'yes'

Runningit like this, the figure looks fine. However, if I switch off the bold part, the figure is dark red (as the stat analysis would suggest). 

In the statistic script, I don't indicate the baseline again and I've no clue how to implement it. Do you think that could be the problem and has anybody a suggestion how to address the problem? 

If that is actually the main issue then I'm hardly the first encountering this problem.

Kind regards,
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