[Mne_analysis] SNR estimate for single trials

Bharadwaj, Hari M hbharadw at purdue.edu
Sun Apr 2 10:19:13 EDT 2017
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Hi Ana and Alex,

I am not so sure about specifying a low SNR for single trials... Yes, it's true of course that single trials are noisier, but often single trial  processing in the source space is followed by combining across trials.. So in many (but not all) instances, it is useful to have a consistent inverse operator (specifying a fixed SNR... and for dSPM scaling the noise cov by a fixed number of trials).

For instance, if you did inverse first on single trials and then averaging in source space vs. average across trials in sensor space first and then do inverse, you would get different answers if you specified different SNRs for the two cases.

This issue came up before, and the 3.0 was used to make them consistent:

https://mail.nmr.mgh.harvard.edu/pipermail//mne_analysis/2014-April/002066.html

https://github.com/mne-tools/mne-python/pull/1237

Just something to keep in mind depending on how you are using single trial inverses.


- Hari

________________________________________
From: mne_analysis-bounces at nmr.mgh.harvard.edu <mne_analysis-bounces at nmr.mgh.harvard.edu> on behalf of Alexandre Gramfort <alexandre.gramfort at telecom-paristech.fr>
Sent: Thursday, March 30, 2017 7:09 AM
To: Discussion and support forum for the users of MNE Software
Subject: Re: [Mne_analysis] SNR estimate for single trials

hi Ana,

yes 1 is typically what is used if you estimate things on single trials.

I think we should update this example to clarify / change this.

See https://github.com/mne-tools/mne-python/issues/4131

Alex

On Thu, Mar 30, 2017 at 6:47 AM, A. Klimovich-Smith <ak798 at cam.ac.uk> wrote:
> Hello everyone,
>
> I want to ask what would be the recommended SNR amplitude estimate when
> computing single trial source estimates with
> mne-python(apply_inverse/apply_inverse_epochs)?
>
> I looked at this tutorial
> http://martinos.org/mne/stable/auto_examples/inverse/plot_compute_mne_inverse_epochs_in_label.html
>
> and for single trial SNR is kept the same as for the evoked data -
> default 3. Would it not make sense to reduce it to less (e.g. 1, I have
> been using previously with mne-c) if we know that single trials are much
> noisier?
>
> Thanks for your help,
> Ana
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