[Mne_analysis] Auditory ROI

[Bharadwaj, Hari M]

        External Email - Use Caution        

Also sometimes in with bilateral auditory ROIs you can have the head position affect the SNR asymmetrically.. For example if a subject with a smaller head resting on the helmet such that their left is touching and have a larger gap on the right, you'd something like what you are seeing. Measuring and correcting for head position can help get the right localization but won't help recover the lost SNR in such cases.


Best,

Hari

​



--
Hari M. Bharadwaj, Ph.D.
Assistant Professor of Speech, Language, and Hearing Sciences
Assistant Professor of Biomedical Engineering
Lyles-Porter Hall
Purdue University
715 Clinic Drive, Room 3162
West Lafayette, IN 47907
(765) 496-2249
hbharadwaj at purdue.edu<mailto:hbharadwaj at purdue.edu>
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________________________________
From: mne_analysis-bounces at nmr.mgh.harvard.edu <mne_analysis-bounces at nmr.mgh.harvard.edu> on behalf of Matti Hamalainen <msh at nmr.mgh.harvard.edu>
Sent: Sunday, December 9, 2018 10:14 AM
To: Discussion and support forum for the users of MNE Software
Subject: Re: [Mne_analysis] Auditory ROI

Hi,

MNE or dSPM should not have a problem with correlated sources like LCMV. However, if the auditory responses from a previous tone extend to the period which is used in the noise covariance calculation interesting things may happen. What happens if you use an empty room noise covariance. What do the MNE signals (not dSPM) look like?

- Matti

On Dec 9, 2018, at 10:03 AM, Bert Liu <bert.smt02g at nctu.edu.tw<mailto:bert.smt02g at nctu.edu.tw>> wrote:


Hi,

Thanks for your reply, Alex.
Yeah, you might be right.
Noa said "single stereo tones", so it may be the correlated sources problem.

From my experience, dSPM could be stable in some cases of presenting correlated sources in M/EEG. But the original LCMV beamformer will not be able to localize and reconstruct the correlated sources because of its unit-gain constraint and the cancellation phenomenon. Moreover, recently, some scholars are tackling this problem, so if some people need very accurate source localization, I would recommend newly advanced algorithms to them.


Bert


Alexandre Gramfort <alexandre.gramfort at inria.fr<mailto:alexandre.gramfort at inria.fr>> 於 2018年12月9日 週日 下午10:27寫道：
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hi,

> This is cancellation phenomenon in signal processing. To be more specific in neuroimaging of MEG/EEG, when you send the same sound simultaneously to each ear of a subject, like you mentioned single stereo tones, there will be temporally correlated sources on bilateral A1s in the MEG or EEG signals recorded from the subject. Highly temporally correlated sources in an MEG or an EEG will cause the problem you mentioned. Furthermore, this phenomenon can be explained by math. So, if you want to know more, I can give you some references.

I think that Noa is using MNE-dSPM so I am not sure it is a problem of
correlated sources.

> Solution to this problem: Noa, you need to use advanced source localization algorithms to localize the true source grids and reconstruct the distortionless time-courses of correlated sources. But I am not familiar with MNE, so I don't know which advanced algorithms are available in MNE software to address this problem. However, I know some available algorithms in other toolboxes.

see what MNE has in store:
http://martinos.org/mne/stable/auto_examples/index.html

you can use MNE/dSPM/sLORETA/eLORETA with make_inverse_operator
you have most beamformers (make_lcmv, make_dics) as well as
sparsity based solvers that output dipole sets such as mixed_norm,
tf_mixed_norm, music, gamma_map etc.

Alex

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---------

Matti Hamalainen, Ph.D.
Athinoula A. Martinos Center for Biomedical Imaging
Department of Radiology
Massachusetts General Hospital

msh at nmr.mgh.harvard.edu<mailto:msh at nmr.mgh.harvard.edu>
mhamalainen at partners.org







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