[Mne_analysis] MNE source estimate analysis with multiple conditions

[Marijn van Vliet]

Dear Lyam,


the reason why you see a difference between MNE(cond1) - MNE(cond2) and 
MNE(cond1 - cond2) is because of the dipole orientations. The source 
estimate only retains the magnitude of the dipoles. See here for some 
more information about what is going on:

https://4006-1301584-gh.circle-artifacts.com/0/home/ubuntu/mne-python/doc/_build/html/auto_tutorials/plot_dipole_orientations.html


When using fixed orientations, there should not be any difference. When 
using loose orientations (the default), MNE(cond1 - cond2) is in my 
opinion the correct way.


regards,
Marijn.

On 04/06/2017 06:42 PM, Lyam Bailey wrote:
>
> Dear MNE users,
>
>
> I am analysing surface-based source estimates computed from evoked MEG 
> data. I would like to extract peak amplitude times from source 
> estimates of the *difference* between two experimental conditions 
> (exp. and control), and as far as I can tell there are two approaches 
> to this. One is to calculate the difference prior to computing source 
> estimates (i.e: exp. evoked - control evoked) and then compute source 
> estimates (.stc) based on the returned array. Another is to generate 
> source estimates for each condition, and then subtract the returned 
> stc files (exp.stc - control.stc) Unfortunately, these two approaches 
> yield slightly different results (I suspect this is due to noise 
> generated by the .stc subtraction) - so which would be most prudent? 
> Alternatively, is there a different (more robust) approach that I 
> could use?
>
>
> Thanks in advance for any help!
>
>
> Regards,
>
> Lyam
>
>
>
> ---------------------------------------------------------
>
> Lyam Bailey, BSc.
>
> Graduate Student
> Department of Psychology & Neuroscience
> Dalhousie University
>
>
>
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