[FieldTrip] combining magnetometers and planad gradiometers for analysis

Stephan Moratti smoratti at psi.ucm.es
Fri Jun 3 16:06:28 CEST 2011

Hi everyone,

Thanks Alexandre for the info. I went a little bit through the FT code and it seems that it reads the raw data without applying the SSP vectors on the data (raw.proj is empty!!). I saw in mne_ex_read_raw.m that you have to activate the projectors and then get the proj matrix with mne_make_projector_info
It is a chan by chan matrix. So adding the proj matrix to the raw structure I understand that by using fiff_read_raw_segment
.m I get the data filtered by the SSP vectors. So now my stupid? question: If I just multiply the grad.tra matrix by the proj matrix, this would fix everything (plotting topos and leadfield calculation???)


El 03/06/2011, a las 15:30, Alexandre Gramfort escribió:

> Hi everyone,
>> I don't know enough about the elekta-software/mne-software to know what is
>> happening to the data when the ssp vectors are computed, but once we know
>> enough details it should be straightforward to build it into fieldtrip.
> SSP vectors are stored in fif files and applied to data only if requested.
> In a typical MNE workflow, the SSP vectors are no directly applied to the raw
> file (avoid data duplication on disk) but rather to the noise covariance matrix
> and consequently in the whitening matrix. When computing an inverse solution,
> the whitening matrix is used on the data and the lead field, hence taking
> into account the SSP vectors.
> Hope this helps.
> -- 
> Alexandre Gramfort, PhD
> gramfort at nmr.mgh.harvard.edu
> Dept. of Radiology MGH Martinos Center / Harvard Medical School
> http://www-sop.inria.fr/members/Alexandre.Gramfort/
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Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)


Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)

email: smoratti at psi.ucm.es
Tel.:    +34 679219982

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