[Mne_analysis] group dSPM?

Hari Bharadwaj hari at nmr.mgh.harvard.edu
Fri Jun 8 12:12:35 EDT 2012
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Question: Why is the noise normalization the same for the 3 orientations?
Shouldn't it depend on the 3 lead fields?

Hari

On Fri, June 8, 2012 12:01 pm, Alexandre Gramfort wrote:
>>  If you combine using A = x^2 + y^2 + z^2 (i.e without the square root
>> or
>> square what MNE gives you) and if x,y,z are *after noise normalization*,
>> then it is reasonable to assume that A is chi2 as long as the noise
>> covariance was computed using a large number of points, I wouldn't be
>> concerned about variances being different since each has approximately
>> variance 1 in the null...
>
> the noise normalization is the same for x, y and z and as you regularize
> more the tangential components than the radial I don't think the
> variance will be
> the same even when you apply dSPM to noise. But I should check as it's
> just an intuition.
>
>> The maps we have gotten from running long permutation tests at the group
>> level and then thresholding using this transformation look very similar.
>> So our current practice is to use this transform and run the usual
>> parametric analyses and invest time in running permutations as
>> confirmation once we see something we like.
>
> ok. Thanks for sharing your experience.
>
> Alex
>
>
>


-- 
Hari Bharadwaj
PhD Candidate, Biomedical Engineering,
Boston University
677 Beacon St.,
Boston, MA 02215

Martinos Center for Biomedical Imaging,
Massachusetts General Hospital
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hari at nmr.mgh.harvard.edu
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