[FieldTrip] MEG Time-Frequency testing (ft_freqstatistics)

[Nathan Weisz]

hi kambiz,

did you look at the actual p-values of you clusters?

the code that you posted plots only the positive cluster (doesn't mean it's significant). so it's no surprise that you don't see a blue blob, because you masked it. look at data structure and there should also be a field 'negclusters' and a 'negclusterlabelmat'.

good luck,
n

On 16.12.2010, at 09:21, Eric Maris wrote:

> Kambiz,
> 
>>> Have a look at the (channel,frequency)-specific paired t-tests.
>> I am not sure exactly what you mean. By 'specific' do you mean sample
>> wise testing in a narrow frequency range?
> 
> Sorry, I forgot that you have time resolution. I mean the
> (channel,time,frequency)-specific paired t-tests, which are in the output of
> freqstatistics.
> 
> 
> Best,
> 
> Eric
> 
> 
>> 
>> -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
>> -------------------------------------------------------------
>> ________________________________________
>> From: fieldtrip-bounces at donders.ru.nl [fieldtrip-bounces at donders.ru.nl]
>> On Behalf Of Eric Maris [e.maris at donders.ru.nl]
>> Sent: Wednesday, December 15, 2010 5:36 PM
>> To: 'Email discussion list for the FieldTrip project'
>> Subject: Re: [FieldTrip] MEG Time-Frequency testing (ft_freqstatistics)
>> 
>> 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>
>>> ------------------------------------------------------------
>> 
>> 
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>> 
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> 
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip