[Mne_analysis] Noise covariance matrix

[Laura Munkki]

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Hi Denis,
1. If the raw data is filtered before the ICA, should one filter averaged
responses again before source modelling?
2. In case of the situation I described above, is it possible to use NCM
calculated for unfiltered NCM-epochs, or it is totally wrong?
Thank you again!


On Thu, Mar 26, 2020 at 5:19 PM Denis A. Engemann <
denis-alexander.engemann at inria.fr> wrote:

>         External Email - Use Caution
>
> Hi Laura,
>
> To me the safest thing is bandpass filtering at raw stage, e.g., prior to
> ICA.
> Then you keep processing identical for data and noise covariance and just
> use the baseline segments from the otherwise  identically processed epochs.
> Have you tried that?
>
> Denis
>
> > On Mar 26, 2020, at 4:11 PM, Laura Munkki <lauramunkki at gmail.com> wrote:
> >
> >         External Email - Use Caution
> >
> >
> > Hi Denis,
> > Thank you very much for your reply.
> > I did maxfiltering and ICA for the raw data, so these steps are applied
> for both types of epochs, evoked responses and NCM. But I did not use any
> band-pass filters before averaging. I filtered only averaged ERPs just
> before source reconstruction. So, if I filter NCM epochs, it will not be
> the same. My question is: when should I apply a band-pass filter for the
> NCM? I tried to apply it to the NCM-epochs file, but the result was
> distorted: instead of sources around auditory cortex I've got several
> sources in unpredictable locations. But when I tried to use NCM calculated
> for unfiltered NCM-epochs, the sources were around auditory cortex and had
> much stronger amplitude.
> > Looking forward for your answer,
> > Thank you very much for helping me,
> > Laura.
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