Time frequency Analysis!

[Jan Mathijs Schoffelen]

Dear Muthuraman,

It pleases us that we finally got you to try multi-tapers for your spectral
analysis! Sometimes it's hard convincing people, but in the end...

First of all there's a typo in your configuration for the frequency
analysis; this does not explain your results, but as an extra service to you
I'd like to point it out. You specify cfg.ouput, where I guess you mean
cfg.output. Moreover, since you have an EMG-channel in your data, you might
be interested in computing the coherence, but therefore you have to specify
cfg.output = 'powandcsd'.

Regarding your nans: did you check whether there are any numbers in
TFRmult.powspctrm. If this is the case, your problem most likely arises in
the plotting. You specify cfg.baselinetype = 'relative', but you do not
specify the baseline-interval. Do you get a warning when executing the
singleplotTFR-function?
If there are only nans in your TFRmult, then I don't get it, because your
configuration looks OK to me?

By the way, which version of fieldtrip are you using? If you are using an
old one, it might be worthwile to download the latest version (there's a
daily update on the FTP-server, you can get there through the
fieldtrip-website), and try the script again (with the small changes
suggested).

Yours,

Jan-Mathijs


-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Muthuraman Muthuraman
Sent: Tuesday, January 30, 2007 3:40 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] Time frequency Analysis!

Hello Fieldtrippers,

I have question regarding the Time-Frequency analysis using tapers,
'mtmconvol' or time frequency analysis using wavelets 'wltconvol'
these are the parameters i use, i get all the values to be Nan's
Is there something wrong which i need to change in the parameters for the
timefrequency analysis

hdr     = read_fcdc_header('pd_mof_tr0_c_0306.cnt');
emgindx = strmatch('M', hdr.label);
rstindx = setdiff(1:length(hdr.label),emgindx);

trl = [];
trl(:,1) = [21:1000:74520-1000]';
trl(:,2) = [1020:1000:74520]';
trl(:,3) = 0;


cfg.dataset = 'pd_mof_tr0_c_0306.cnt';
cfg.trl     = trl;
cfg.channel = hdr.label(rstindx);
cfg.blc     = 'yes';
data        = preprocessing(cfg);

cfg.channel  = hdr.label(emgindx);
cfg.hpfilter = 'yes';
cfg.hpfreq   = 10;
cfg.rectify  = 'yes';
emg          = preprocessing(cfg);

for j = 1:length(emg.trial)
  emg.trial{j} = blc(emg.trial{j});
end
data         = appenddata([],data,emg);

%---freqanalysis-mtmconvol
cfg=[];
cfg.ouput='pow';
cfg.sgn='data';
cfg.method='mtmconvol';
cfg.channel    = channelselection({'all' 'M1'}, data.label);
cfg.foi=2:2:30;
numfoi=length(cfg.foi);
cfg.t_ftimwin=zeros(1,numfoi);
cfg.t_ftimwin(:)=0.5;
cfg.tapsmofrq=zeros(1,numfoi);
cfg.tapsmofrq(:)=10;
cfg.toi=-0.5:0.05:1.0;
cfg.taper='dpss';
cfg.pad=2;
cfg.keeptrials='no';
TFRmult=freqanalysis(cfg,data);

%---Plotting
cfg=[];
cfg.baselinetype='relative';
cfg.zlim=[-2e-27 2e-27];
cfg.showlabels='yes';
cfg.channel='C3';
singleplotTFR(cfg,TFRmult);


Thanking you

With regards
M.Muthuraman.

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