[FieldTrip] Questions about time frequency analysis of EEG data

[Arti Abhishek]

Dear fieldtrip community,

I am running time frequency analysis on my EEG data and when I subtract the
response between conditions, the difference condition has much higher
amplitude. Could someone suggest what is wrong here?

Please find the image here:
https://www.dropbox.com/s/kh5uzz8000fmh1b/tfr.pdf?dl=0

and here is my script

cfg                      = [];
cfg.trials              = find(s01_ica_clean_artrel_reref.trialinfo==102);
cfg.channel          = 'EEG';
cfg.method           = 'wavelet';
cfg.width              = 7;
cfg.output             = 'pow';
cfg.foi                  = 2:2:40;
cfg.toi                  = -0.4:0.02:0.5;
s01_cond1           = ft_freqanalysis(cfg, s01_cond1_preprocess);
% difference
cfg=[];
cfg.parameter='powspctrm';
cfg.operation ='x1-x2';
s01_difference     =ft_math(cfg, s01_cond1, s01_cond2);
% plot
cfg                     = [];
cfg.baseline=[-0.4 -0.1];
cfg.zlim=[-0.5 0.5];
cfg.xlim=[-0.4 0.5];
cfg.baselinetype = 'relchange';
cfg.layout              = lay;
cfg.interactive         = 'yes';
cfg.channel={'FZ'};
subplot (1,3,1)
ft_singleplotTFR(cfg, s01_cond1);
title('deviant');
subplot (1,3,2);
ft_singleplotTFR(cfg, s01_cond2);
title('standard');
subplot (1,3,3)
ft_singleplotTFR(cfg, s01_difference);
title('difference');

Thanks,
Arti
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