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

Stephen Whitmarsh stephen.whitmarsh at ki.se
Wed Jul 29 13:53:07 CEST 2015

Dear Mick,

The designmatrix looks fine to me.
I have not idea what might go wrong, but if I were you I would do the following checks:

1) Calculate the difference of the TFRs by subtracting the two (manually or with ft_math) after you did the baselinecorrection for each - i.e. exactly what you were giving to freqanalysis. Then plot the results using topoplotTFR without any baseline in the configuration of topoplotTFR. This should tell you whether the right stuff is going into freqstatistics.

2) First do the freqanalysis without averaging over frequencies or using any clustering. Then plot the t-values (of every time-frequency point) using ft_topoplotTFR.

This should give you a good first idea whether the statistics are behaving as you would expect.

Hope this helps,

From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of mick.lehmann at uzh.ch [mick.lehmann at uzh.ch]
Sent: 29 July 2015 12:48
To: fieldtrip at science.ru.nl
Subject: Re: [FieldTrip] Baseline Correction using 'relchange' or 'db'

Dear Stephan,

the whole script with the designmatrix looks as follows. It is a within-subject design with two conditions.

load ga_TFCond1
load ga_TFCond2
load neighbours

cfg = [];
cfg.channel          = 'all';
cfg.latency          = [0 2];
cfg.avgovertime      = 'yes';
cfg.frequency        = [5 7];
cfg.avgoverfreq      = 'yes';
cfg.method           = 'montecarlo';
cfg.statistic        = 'ft_statfun_depsamplesT';
cfg.correctm         = 'cluster';
cfg.clusteralpha     = 0.05;
cfg.clusterstatistic = 'maxsum';
cfg.minnbchan        = 2;
cfg.tail             = 0;
cfg.clustertail      = 0;
cfg.alpha            = 0.05;
cfg.numrandomization = 500;
cfg.neighbours       = neighbours;

subj = 20;
design = zeros(2,2*subj);
for i = 1:subj
  design(1,i) = i;
for i = 1:subj
  design(1,subj+i) = i;
design(2,1:subj)        = 1;
design(2,subj+1:2*subj) = 2;

cfg.design   = design;
cfg.uvar     = 1;
cfg.ivar     = 2;

stat = ft_freqstatistics(cfg, ga_TFCond1, gaTF_Cond2);

Thanks a lot for your efforts!

Kind regards,
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