[Mne_analysis] equivalence of averaged single trial STCs and evoked STCs

[Alexandre Gramfort]

hi Hari,

>     Just to follow up on your comment.. What do you mean when you say, that dSPM is "not a plain scaling of the estimates"?

yes it is. I wasn't clear. What I meant is that when you change nave you
don't just change the scale of dSPM. At least numerically it is not the case
as confirmed by a tiny experiment.

https://gist.github.com/agramfort/9579975

> For any *given vertex*, the MNE time course and the dSPM time course (or any other linear inverse time course) are indeed different only by a scale factor.  Of course, the MNE and dSPM *spatial maps* are not scaled versions of each other because the multiplier that relates the dSPM estimates to the MNE estimates is different for each vertex (the point of noise normalization being to improve the spatial map).

yes no confusion here.

> Also, if the baseline period is used for noise cov estimation, it is not clear to my why post hoc normalization by the baseline standard deviation is different from dSPM (even mathematically)..

dSPM is not exactly a z-scoring.
if it were the case the std deviation of each time course during
baseline would be exactly 1.
Also when you use a noise cov in dSPM, you often add a regularization
and the inverse code clips the tiny eigenvalues.

Alex