[FieldTrip] one-sample cluster test

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Tue Mar 27 15:48:07 CEST 2012

Dear Ulrich,

First of all, you might want to use the Neural Activity Index (NAI), as 
also described in the tutorial:

Then, to answer your question, I am tempted to say that this would be an 
invalid approach when dealing with power, so in frequency-space. Power 
obviously has a lower bound, so that the average of any random 
collection of power values will never be 0. Though, what you are 
suggesting is the same as a regular t-test, isn't it?
In case you are dealing e.g. with am LCMV beamformer, I am not quite 
sure, but the null-hypothesis you suggested (amplitude==0)  sounds fair.

In any case, building a surrogate distribution same mean and variance 
than your data might be a better way to deal with your problem. That 
should be easily doable in Matlab without any need to implement this in 
FieldTrip. And note that the MC problem is always present, but a 
cluster-based correction (similar to Bonferroni, but correcting by the 
number of voxels in the cluster not by the number of all voxels) sounds 
legitimate to me. Afair, that's how it's done in FT.


On 3/27/2012 3:00 PM, Pomper, Ulrich wrote:
> Dear list members,
> this topic was discussed some time in 2008, but it seems to me no
> conclusion was found.
> I would like to find source activity that differs significantly from
> zero. I could run a one sample t-test for every voxel and end up having
> a huge MC problem, or (preferably) use some kind of cluster based
> permutation statistics. However, the option for a one sample cluster
> test is not implemented in FT.
> Would it be correct to test the data from my experimental condition
> against a set of data containing all zeros using a cluster based
> permutation test?
> Any help is very much appreciated!
> Best, Ulrich
> _______________________________________________
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> fieldtrip at donders.ru.nl
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Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group

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E-Mail: jm.horschig at donders.ru.nl
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