Time frequency Analysis!

Jan Mathijs Schoffelen Jan.Schoffelen at FCDONDERS.RU.NL
Wed Jan 31 11:21:46 CET 2007

Dear Muthuraman,

In your last mail you wrote:
>I do get any warning while executing the singleplotTFR function
Does this mean that you do, or do not get any warnings?

Please note that it should read cfg.ouTput (without the capital letter T)

>cfg.baselinetype=[0.1 1.0];
This is obviously wrong: cfg.baselinetype specifies how to do baseline
correction. This can be 'relative' 'absolute' or 'relchange'. Please consult
the help of this function, or of freqbaseline.m
You specify the baseline-interval with cfg.baseline.

>cfg.zlim=[-2e-27 2e-27];
Your values seem to be completely clipped. Did you try around with different
zlims? A typical value of 2e-27 applies to MEG, when no relative or
relchange baselining is involved. EEG is measured in mV's, and power is
measured in mV's-squared, so something in the order of 2e-6 seems more
appropriate to me.

Note that the nans arise when there is not sufficient data in the timewindow
outside [0.25 0.75]. This of course is due to the fact that your data is
only defined between [0 1], and your timewindow for the time-frequency
analysis is 0.5 seconds.



>From: Jan Mathijs Schoffelen <Jan.Schoffelen at FCDONDERS.RU.NL>
>Reply-To: FieldTrip discussion list <FIELDTRIP at NIC.SURFNET.NL>
>Subject: Re: [FIELDTRIP] Time frequency Analysis!
>Date: Tue, 30 Jan 2007 17:34:44 +0100
>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
>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
>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
>-----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
>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});
>data         = appenddata([],data,emg);
>cfg.channel    = channelselection({'all' 'M1'}, data.label);
>cfg.zlim=[-2e-27 2e-27];
>Thanking you
>With regards
>Tickle your funny bone with Rahul Phondke

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