[FieldTrip] (no subject)

jan-mathijs schoffelen jan.schoffelen at donders.ru.nl
Thu Oct 27 20:03:18 CEST 2011


Dear Seb,

A few comments to your question:
-I don't really remember why 'pcc' as a method shouldn't work, but I believe that a straightforward explanation why it is disabled is that once-upon-a-time the functionality you are trying to apply was designed for 'dics' as method (and as such originates from the pre-pcc era. I wonder whether it will work for cfg.method = 'dics'.
-Even if it would work, it is a very computationally heavy method: data are shuffled across the conditions at the channel level and spatial filters are computed (for both conditions) for each randomization. When we implemented this method, back in the old days, we quickly abandoned it again because of the discrepancy between the computation time and the computational resources. 
-The functionality still being present (I still assume that it kind of works) is the consequence of us being quite devoted to backward compatibility, although I don't want to bet my money on it to work (for dics).
-Nowadays, I would advise to do the randomisation testing at the source level, i.e. computing a single set of spatial filters common to both conditions (the so-called common filter approach), and then use ft_sourcestatistics for the randomization testing. To get started, you could have a look at: http://fieldtrip.fcdonders.nl/example/common_filters_in_beamforming?s[]=common&s[]=filter, although I notice that the final step (calling ft_sourcestatistics is not explained there).


Cheers,

JM

On Oct 27, 2011, at 7:35 PM, miellet at psy.gla.ac.uk wrote:

> Hello,
> I'm trying to use ft_sourceanalysis with pcc. I specify the volume conductor model, the sensor information and a grid with pre-computed leadfields.
> I tried to compute the statistics over the source parameters between two conditions as indicated in the documentation (ft_sourceanalysis(cfg, freqA, freqB) with randomization).
> I get an error linked to the condition:
> if nargin>2 && strcmp(cfg.prewhiten,'no')
> I couldn't find any information about this cfg.prewhiten parameter.
> this part of the code if commented by
> % HACK: requires some extra defaults
> % HACK: use some experimental code
> Does anyone know if this part is functional yet please?
> Thanks,
> Sebastien
> 
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Jan-Mathijs Schoffelen, MD PhD 
Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands
J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

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