[FieldTrip] missing pos in beamforming

Jason Chan chan at med.uni-frankfurt.de
Fri Mar 16 15:17:09 CET 2012

Hi Michael,


Many thanks for your informative reply.  I was able to use the reverse normalization technique and eliminated the ft_sourceinterpolate and ft_volumenormalise commands.

However, after I subtract ‘sourceA’ from ‘sourceB’ I now get the error “different grid locations in source reconstructions” when I try to do a ft_sourcegrandaverage.  Any suggestions would be very welcome.


Thanks in advance.



From: fieldtrip-bounces at donders.ru.nl [mailto:fieldtrip-bounces at donders.ru.nl] On Behalf Of Michael Wibral
Sent: Mittwoch, 14. März 2012 20:29
To: Email discussion list for the FieldTrip project
Subject: Re: [FieldTrip] missing pos in beamforming


Dear Jason,

the pos indicates where the original sources were (i.e. on a regular grid with a certain spacing or self-defined). After interpolation this information does not reflect the data anymore. I would suggest to use Ingrid nieuwenhuis famous reverse normalization technique to create individual subject grids taht all match in MNI space - the script is found on the ft website. Sourceinterpoltae should really only be used for plotting IMHO.


Gesendet: Mittwoch, 14. März 2012 um 17:28 Uhr
Von: "Jason Chan" <chan at med.uni-frankfurt.de>
An: fieldtrip at donders.ru.nl
Betreff: [FieldTrip] missing pos in beamforming 


I am adapting the beamformer tutorial to my data.  When I sourceinterpolate the subtracted sourceA from sourceB data, the ‘pos’  disappears.  This seems to be important for the volume normalization and Grand Average.  I am running Fieldtrip version: 20110917.  I have placed the code below.


Many thanks in advance.





for i=1:length(Young_CombineFilter_beamform_16_3);


    Young_CombineFilter_sourceDiff_16_3{i} =Young_CombineFilter_beamform_16_3{i}.sourceA;

    Young_CombineFilter_sourceDiff_16_3{i}.avg.pow =(Young_CombineFilter_beamform_16_3{i}.sourceA.avg.pow - Young_CombineFilter_beamform_16_3{i}.sourceB.avg.pow)./Young_CombineFilter_beamform_16_3{i}.sourceB.avg.pow;


    cfg            = [];

    cfg.downsample = 2;

    cfg.parameter  = 'avg.pow';

    cfg.anatomy    = mri{i};



    Young_CombineFilter_sourceDiffInt_16_3{i}=ft_sourceinterpolate(cfg,Young_CombineFilter_sourceDiff_16_3{i}, mri_young{i});



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