[FieldTrip] Problems time-frequency analysis of Local Field Potential

[Eelke Spaak]

Dear Zuyue,

When you invoke ft_singleplotTFR, do you specify a means of baseline
correction and/or explicit z-limits (i.e., limits of the color axis)?
When looking at raw power (i.e., not contrasted), it is advisable to
use a baseline correction in order to see something. Also, specifying
z-limits of a different order of magnitude than your data will of
course lead to all blue plots.

You should take a look at the time-frequency analysis tutorial,
particularly the part about visualization:
http://fieldtrip.fcdonders.nl/tutorial/timefrequencyanalysis#visualization

If you still don't see anything after you use baseline correction (or
plot a contrast instead) and have proper z-limits, there might be
something else wrong.

Best,
Eelke

2011/12/16 chenzuyue <chenzuyue at live.cn>:
> Hi, everyone,
>
> I am a new user of FieldTrip. In my study, I want to computes the difference
> of time-frequency representations of event-related LFP in two conditions.
>
> The data in the first condition is a 4 X 1100 X 103 matrix (Nchan X Nsamples
> X Ntrials). The data in the second condition is a 4 X 1100 X 107 matrix. The
> data reformatted are as follows:
>
> dataset1.label (4 X 1 cell );
>
> dataset1.fsample 1000;
>
> dataset1.trial (1 X 103 cell );
>
> dataset1.time (1X 103 cell); % time is from -100ms to 999ms.
>
>
> dataset2.label (4 X 1 cell );
>
> dataset2.fsample 1000;
>
> dataset2.trial (1 X 107 cell );
>
> dataset2.time (1X 107 cell ); % time is from -100ms to 999ms.
>
>
> The frequency interested is 0-100Hz. The method to calculate TFRs is the
> multitaper method. The configuration is as below:
>
> cfg = [];
> cfg.output     = 'pow';
> cfg.method     = 'mtmconvol';
> cfg.foi        = 1:2:100;
> cfg.t_ftimwin  = 5./cfg.foi;
> cfg.tapsmofrq  = 0.4 *cfg.foi;
> cfg.toi        = -0.1:0.05:1;
> cfg.pad        = 'maxperlen';
> TFRmult1 = ft_freqanalysis(cfg, dataset1);
>
> But after running, I can not get the right results. When I use
> ft_singleplotTFR to plot graph, there is only blue color. I wonder whether
> the process and configuration is right.
>
> The method is from one paper of E Maris and R Oostenvels published on the
> Journal of Neuroscience Methods.164(2007), 177-190; Figure 3.
> http://www.ncbi.nlm.nih.gov/pubmed/17517438
>
> Any help is much appreciated.
>
> Yours Sincerely,
>
> Zuyue
>
>
>
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