# Significance test frequency power decrease baseline vs stimulation

Thomas Dijkman t.b.dijkman at STUDENT.UTWENTE.NL
Thu Jun 26 00:09:33 CEST 2008

```Hi,

For my bachelor's assignment, I'm trying to find a visual stimulus of a hand
movement that triggers the 'largest' modulation of the EEG. I.e. , when the
subject looks at a right hand movement, literature suggest a decrease in
power in the 8-13 Hz band, relative to a baseline period around electrode
position C3.
I'm trying to use Fieldtrip's freqstatistics.m function to test this
decrease in power for significance. Following a tutorial in the Fieldtrip wiki,
http://www2.ru.nl/fcdonders/fieldtrip/doku.php?id=fieldtrip:documentation:tutorial:statistics&s=freqstatistics#3.2_permutation_tests_for_time-frequency_representationswithin_trial_experiments

which I thought applied to my situation gave me a lot of error messages.

I've already redefined my trials, so I have a separate set of trials, one
containing 2 seconds of baseline, and one containing 2 seconds of stimulus.
The baseline time axis is shifted so it overlaps the stimulus time axis

I then use this code to calculate TFR's for those datasets:

cfgfreq.method = 'mtmconvol';
cfgfreq.output = 'pow' ;
cfgfreq.taper = ' hanning' ;
cfgfreq.foi = 8:1:13;
cfgfreq.t_ftimwin = 10./cfgfreq.foi;
cfgfreq.toi = 5:1/100:7;
cfgfreq.tapsmofrq = cfgfreq.foi*0.4;
[baselineTFR] = freqanalysis(cfgfreq,baselinedata);
[stimulusTFR] = freqanalysis(cfgfreq,stimulusdata);

And then I have to do the significance test.

cfg = [];
sfg.method = 'analytic';
cfg.statistics = 'actvsblT';
cfg.alpha = 0.05;
?
[stat] = freqstatistics(cfg,stimulusTFR,baselineTFR);

I think I have to do something with the design matrix, but I can't find
anything about that in the wiki (or the rest of the internet).

Thanks,

Thomas

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