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

[Hari Bharadwaj]

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

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).

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).. 

Hari




Hari Bharadwaj
PhD Candidate, Biomedical Engineering,
Auditory Neuroscience Laboratory
Boston University, Boston, MA 02215

Martinos Center for Biomedical Imaging,
Massachusetts General Hospital
Charlestown, MA 02129

hari at nmr.mgh.harvard.edu
Ph: 734-883-5954

On Mar 15, 2014, at 3:58 PM, Alexandre Gramfort <alexandre.gramfort at telecom-paristech.fr> wrote:

>> Also, just wanted to quickly add that in my understanding, what dSPM is
>> essentially trying to achieve is the same kind of normalization as would
>> result when you do MNE first and then scale by the baseline..
> 
> it's the same objective but it's mathematically different.
> 
> one more thing to add is that the nave also plays a role
> in the scaling of the regularization parameter. It scales the noise
> cov used in dSPM but it's not a plain scaling
> of the estimates.
> 
> Alex
> 
>