Multitaper!

[Muthuraman Muthuraman]

Hello Fieldtrippers,

I am using for the first time the mulitaper analysis for a TMS study where for every 3 sec a TMS-pulse is given for a 3min duration 
so i have like 100 trials, i would like to calculate the coherence between two EEG channels within a interval of -0.5 s to 1.5 s.


As in the tutorial for the time frequency analysis the function i am using for calculating the coherence is as follows


[event] = read_fcdc_event('JO_single_pulse_no_block_Vorinervat.vmrk');% reading in the marker file
hdr     = read_brainvision_vhdr('JO_single_pulse_no_block_Vorinervat.vhdr');% reading the header file
cfg         = [];
cfg.dataset = 'JO_single_pulse_no_block_Vorinervat.eeg';% data file
cfg.headerfile = 'JO_single_pulse_no_block_Vorinervat.vhdr' ;
cfg.trialdef.eventtype='Stimulus';
cfg.trialdef.eventvalue='S 64';
cfg.trialdef.prestim    = 1.000;
cfg.trialdef.poststim   = 2.000;
cfg     = definetrial(cfg);
cfg.blc     = 'yes';
cfg.blcwindow=[-1.000 0.000];
dataFIC        = preprocessing(cfg);

% For calculating the coherence 
cfg=[];
cfg.output='powandcsd';
cfg.method='mtmconvol';
cfg.channel    = channelselection({'C3','Cz'}, dataFIC.label);
cfg.channelcmb = channelcombination({'C3','Cz'}, dataFIC.label);
cfg.foi=2:1:22;
numfoi=length(cfg.foi);
cfg.t_ftimwin=ones(1,numfoi);
cfg.t_ftimwin(:)=0.5;
cfg.toi=-0.50:0.05:1.500;
cfg.taper='hanning';
cfg.tapsmofrq=ones(1,numfoi);
cfg.tapsmofrq(:)=1;
cfg.pad='maxperlen';
cfg.keeptrials='no';
TFRmult=freqanalysis(cfg,dataFIC);
cfg.keeptrials='yes';
fdmtmfft=freqdescriptives(cfg,TFRmult);

I have attached a plot with this mail which contains very high coherence in the interval -0.75s to 0.75s. Any hint on what is going wrong in the analysis
would be very helpfull.

Sorry for the long mail

Thanking you 

With regards
M.Muthuraman. 

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