[FieldTrip] MEG Time-Frequency testing (ft_freqstatistics)

[Eric Maris]

Dear Kambiz,


> Greetings Fieldstrippers 

"Fieldtrippers" may have connotations that a scientist does not always
appreciate, but what to think of "Fieldstrippers"?
 
> 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! 

Have a look at the (channel,frequency)-specific paired t-tests. Do these
detect the big cold blob? If not, the variance across subjects is probably
large.


Best,

Eric Maris






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>
> ------------------------------------------------------------