[Mne_analysis] group dSPM?

[Alexandre Gramfort]

>  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