[FieldTrip] MEG Time-Frequency testing (ft_freqstatistics)

Stephan Moratti smoratti at psi.ucm.es
Wed Dec 15 21:52:22 CET 2010

Hi Kambiz,

Probably you should consider to use cfg.alpha and cfg.clusteralpha =  
0.025 if you test two sided (cfg.tail and cfg.clustertail=0). Doing  
so, will give you a the p values of 0.05 alltogether.



El 15/12/2010, a las 16:52, Tavabi, Kambiz escribió:

> Greetings Fieldstrippers - Would someone savvy in cluster  
> permutation testing kindly take a look at the attached plots.  
> Briefly, Top left upper & lower panels are conditional grand  
> averaged (n=10), time-frequency representation (TFR) of single  
> virtual electrode. The TFR shows %change in power relative to  
> baseline (i.e., baseline corrected power spectrum). The top right  
> panel is the p-value map of sample-wise paired t-testing (two- 
> tailed) of the data.
> To deal with the multiple comparison problem, I used  
> ft_freqstatistics to carryout out permuation tests on the source  
> space time-frequency representations from my virtual sensors (2), as  
> such the statistics were done without cfg.minnbchan and  
> cfg.neighbours=[ ]. Testing was done on the time-frequency bins  
> throughout the epochs of wide band data (i.e., no averaging over  
> frequencies).
> In the attached file the bottom panel is the plot of the permutation  
> result for the same data and channel in the grand averages. As per  
> advice from other fieldtrip users I created the plot by:
> stat.stat2=stat.stat.*(stat.posclusterlabelmat == 1);
> cfg.zparam='stat2';
> ft_singleplotTFR(cfg, stat);
> When I use ft_clusterplot(cfg, stat); for obvious reasons I get the  
> following error. As I have no apriori freqs interval of interest I  
> am not sure how to get around this.:
> ??? Error using ==> ft_clusterplot at 75
> stat contains multiple frequencies which is not allowed because it  
> should be
> averaged over frequencies
> My problem with the results in the attachment is that in the grand  
> averages there is an obvious event related desynchrony (cold colors,  
> negative values) difference between 0.4-0.8sec; 10-40hz which  
> somehow doesn't get picked up, but the small blip of noise/event- 
> related synchrony (hot colors, positive values) c. 0.5sec at 50Hz is  
> revealed as different between conditions by the permutations! To  
> carry out the permutations I used
> cfg.method           = 'montecarlo';
> cfg.statistic        = 'depsamplesT';
> cfg.correctm         = 'cluster';
> cfg.clusteralpha     = 0.05;
> cfg.clusterstatistic = 'maxsum';
> cfg.neighbours       = [ ];
> cfg.tail             = 0;
> cfg.clustertail      = 0;
> cfg.alpha            = 0.05;
> cfg.numrandomization = 500;
> So I presume that the result is not due to a signs (pos/neg values)  
> issue, if I am using a two-tailed test. Changing cfg.tail &  
> cfg.clustertail to 1 makes little to no difference, and a value of  
> -1 results in errors. Basically, I'd appreciate if someone, based on  
> what is observable in the grand averages, could confirm that the  
> permutation result makes sense? And if not then some advice on what  
> I am doing wrong. Thank you. -Kambiz
> -K.
> ------------------------------------------------------------
> Kambiz Tavabi PhD
> Biomedical Imaging Laboratory
> The Children's Hospital of Philadelphia
> 34th Street and Civic Center Boulevard
> Philadelphia, Pa. 19104
> Tel: 267.426.0302
> email: tavabik at email.chop.edu<mailto:tavabik at email.chop.edu>
> ------------------------------------------------------------
> <TFR_testing.pdf>_______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Department of Basic Psychology
Universidad Complutense de Madrid

Centro de Tecnología Biomédica CBT,
Universidad Politécnica de Madrid,

en la actualidad (currently at) en el
Centro de Magnetoencefalografía Dr. Perez Modrego,
Universidad Complutense de Madrid,
Faculdad de Medicina,
Pabellón 8,
Avda. Complutense, s/n,
28040 Madrid,

email: smoratti at psi.ucm.es
Tel.:    +34 91 394 2186
Fax.:   +34 91 394 2294

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