[Mne_analysis] MNE source estimate analysis with multiple conditions

[Lyam Bailey]

Dear Marijin,


Thanks for your help! I think I see what you're saying, but just to clarify, does MNE(cond1-cond2) refer to source estimates generated from (evoked cond1 - evoked cond2)?


Regards

Lyam


---------------------------------------------------------

Lyam Bailey, BSc.

Graduate Student
Department of Psychology & Neuroscience
Dalhousie University


________________________________
From: mne_analysis-bounces at nmr.mgh.harvard.edu <mne_analysis-bounces at nmr.mgh.harvard.edu> on behalf of Marijn van Vliet <w.m.vanvliet at gmail.com>
Sent: Friday, April 7, 2017 12:43:03 PM
To: mne_analysis at nmr.mgh.harvard.edu
Subject: Re: [Mne_analysis] MNE source estimate analysis with multiple conditions


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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