[FieldTrip] multitaper and NaN

[Silvia Pagano]

Dear list subscribers,

I am an ERPer looking for the first time into the world of time-frequency
analysis. I am trying to perform some multitaper analysis on a data set.
Ideally I would like to perform similar analysis as described in a paper by
Gould et al (2011) on Journal of Neurophysiology. (i.e. in their own words
"Time-frequency analysis was performed on
all epochs using a multitaper approach (2–30 Hz, 0.5-Hz steps, 500-ms
temporal smoothing window, 2-Hz frequency resolution)" )

I have epochs from -1100 ms to 100 time locked to the stimulus onset and I
am trying to replicate the analysis they did. The problem is that I got
boundary effects on all my conditions, namely I obtain NaN in the extreme
100 ms of the time window for all frequencies and for very low frequencies
(e.g. 2-4Hz) I have no data in the whole time window. I thought I had time
windows large enough to avoid boundary effects, however there must be
something I am missing in my code.

Here's what I did following the tutorial:

cfg = [];
cfg.output     = 'pow';
cfg.channel    = 'EEG';
cfg.method     = 'mtmconvol';
cfg.foi        = 2:2:30;
cfg.t_ftimwin  = 5./cfg.foi;
cfg.tapsmofrq  = 0.4*cfg.foi;
cfg.toi        = -1.1:0.02:0.1;
cfg.pad        = 'maxperlen';
TFRmult = ft_freqanalysis(cfg, data);


Does anyone have a clue on this?


Thank you very much

Silvia
-- 
__________________________________

Silvia Pagano PhD student
CIMeC - Center for Mind/Brain Science
Corso Bettini, 31 38068 Rovereto (TN)
Tel. +39 0464 808709
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