tfanalysis - NaN

[Christian Hesse]

Hi Virginie,

the function freqanalysis will return NaNs when a time frequency tile
extends beyond a corresponding data segment. One would usually expect
a "U" shaped padding of NaNs at the boundaries of any TFR which has
longer time windows for lower frequencies. From the cfg options you
specify below I can see that you have a data segment of 1.1 seconds
length and the moving windows cfg.t_tfimwin are quite long at the low
ffrequencies, e.g., 1 Hz = 4 s, 6 Hz  = 0.6666 s. Hence the NaNs seem
perfectly "normal" in this case. The only way to avoid NaN in the
time window of interest (using this type of time-frequency tiling) is
to make your epochs longer.

Hope this helps,
Christian


On 21 Jun 2007, at 20:44, Virginie van Wassenhove wrote:

> Hello again.
>
> I am finding NaN whatever method I use (multitaper and wavelet
> analysis), yet using a different analysis tool with similar
> parameters I obtain clean results.
> epoch length    = 1.1 s
> baseline length = 0.3 s
> sampling rate   = 500Hz
>
> I tried several suggestions listed in the previous message list for
> a similar problem, but none seem to provide reasonable results (aka
> always NaN).
> Also tried with different subjects, no particular error otherwise.
> I am sending a sample script in case someone has a suggestion on
> this...
> Thanks for your help once more!
>
> Virginie
>
> %% ================================================
> % TF analysis - MULTITAPER
> cfg             = [];
> cfg.method      = 'mtmconvol';
> cfg.taper       = 'hanning';
> cfg.output      = 'powandcsd';
> %cfg.channel    = 'all';
> cfg.channel     = 'E75';
>
> %win_length     = 0.128;
> %win_n  = floor(2.*(1.1./win_length)-1);
>
> cfg.foi = 1:5:45;
> %cfg.t_ftimwin = ones(1,win_n).*win_length;
> cfg.t_ftimwin   = 4./cfg.foi;
> %cfg.toi        = -0.3:win_length/2:0.8;
> cfg.toi         = -0.3:0.05:0.8;
>
> % cfg.pad       = 'maxperlen';
> % cfg.keeptrials = 'no';
> % cfg.keeptapers ='no';
> s08_ill_mult = freqanalysis(cfg,s08_ill);
>
> %% ========================
> % plot freq data
> cfg             = [];
> cfg.baseline    = [-0.3 0];
> cfg.layout      = egilay;
> cfg.zlim        = [-0.00001 0.000001];          % a comparer entre
> participants
> % warning off                 % NaN
> clf
> %multiplotTFR(cfg,s08_ill_mult);
> singleplotTFR(cfg,s08_ill_mult);
>
> %% ================================================
> % TF analysis - wavelet
> cfg             = [];
> cfg.method      = 'wltconvol';
> cfg.width               = 4;
> cfg.output       = 'pow';
> cfg.foi                 = 1:2:30;
> cfg.toi                 = -0.3:0.05:0.8;
> s14_ill_wvlt    = freqanalysis(cfg, s14_ill);
> %% ========================
> cfg = [];
> cfg.baseline    = [-0.3 0];
> cfg.zlim        = [-1 1];
> cfg.showlabels = 'yes';
> cfg.layout      = egilay;
> clf
> multiplotTFR(cfg, s14_ill_wvlt)
>
> %% ================================================
>
>
>
>
>
>
> Virginie van Wassenhove, PhD
>
> :::::::::::: contact info  :::::::::::::
> Caltech - Division of Biology
> 1200 E. California Blvd M/C 139-74
> Pasadena CA 91125 USA
> :::::::::::::::::::::::::::::::::::::::::::::::::
> vvw at caltech.edu
> Virginie.van.Wassenhove at gmail.com
> W: 626.395.8959
> http://www.its.caltech.edu/~vvw
>
> :::::::::::::::::: extras ::::::::::::::::::::
> http://www.kiva.org
> http://www.thehungersite.com/
> http://www.agloco.com/r/BBBS1539
> :::::::::::::::::::::::::::::::::::::::::::::::::
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users
> of the FieldTrip  toolbox, to share experiences and to discuss new
> ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/
> archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
>

----------------------------------------------------------------------
Christian Hesse, PhD, MIEEE

F.C. Donders Centre for Cognitive Neuroimaging
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Tel.: +31 (0)24 36 68293
Fax: +31 (0)24 36 10989

Email: c.hesse at fcdonders.ru.nl
Web: www.fcdonders.ru.nl
----------------------------------------------------------------------





----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
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