[Mne_analysis] Noise covariance on Neuromag combined M/EEG

Huovilainen, Tatu M tatu.huovilainen at helsinki.fi
Thu Dec 3 10:56:15 EST 2015
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Hi all,

I'm working with combined M/EEG dataset measured with Neuromag and I'm wondering about the whitening step before ICA. Right now the MEG part of the data is tSSS'd and movement corrected (with cHPI to 'default head position') so the rank seems to end up being around 70. Engemann and Gramfort (2015, below) point out that with combined M/EEG a FA model should be used for the estimation as the noise levels between sensor types are heteroscedastic, but also recommend not to use FA model after the dimensionality has been reduced. How do you recommend I find the noise covariance matrix in my case?

Engemann and Gramfort recommend computing the FA model before the SSS and then applying dimensionality reducing operators to both the data and the covariance estimator. How would this work?

I'm not sure about tSSS, but I have to use at least the movement correction as I'm aiming for ICA decomposition and further analyses in the IC domain. I also have combined M/EEG "empty room" measurement, so a participant not doing anything for a few minutes.

Regards,
Tatu

Engemann, D. A., & Gramfort, A. (2015). Automated model selection in covariance estimation and spatial whitening of MEG and EEG signals. NeuroImage, 108, 328-342.
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