[FieldTrip] Common Filters Question

[Max Cantor]

Ok, I thought something along those lines might be the case, but I just
wanted to make sure. I've never used bugzilla before but I'm sure I can
figure it out, and I'd be glad to help!

Thanks Jan-Mathijs,

Max


On Wed, Jul 16, 2014 at 3:12 AM, jan-mathijs schoffelen <
jan.schoffelen at donders.ru.nl> wrote:

> Dear Max,
>
> I checked out both snippets of code (on the tutorial page and on the
> example page), and to me it seems that you should be able to get away with
> what you call the ‘simple common filter’. The code on the example page to
> me looks unnecessarily complicated (apart from the fact that it is
> incomplete), and seems to be designed to first create a single trial
> representation of the data in source space, before averaging across the
> trials that pertain to a certain experimental condition. If, as I suspect
> it to be so in your case, one is only interested in computing a per
> condition average in source space (in order to be able to do statistical
> inference across a group of subjects), computing and using the common
> spatial filter as per the tutorial should do the trick.
> I guess that the person who wrote the example code for some reason wanted
> to have access to the single trial source data (as per point 3 in the
> section ‘how to do this in fieldtrip’ on the example script page).
> Projection of single trial data to the source level indeed blows up memory
> requirements, and may only be necessary in certain non-standard cases. I
> think it would be good to make this more explicit on the example page
> (thanks for spotting it!). Would you mind helping out with this? It’s a
> wiki after all ;-), and the example code is allowed to be
> adjusted/extended. I suggest that we adjust the page a bit so that we make
> explicit that we can reconstruct single trial data if needed (for this we
> only need to make the example code correct), but that in most cases we can
> work with averages across trials (for this we need to add a section that
> more or less duplicates the creation of the ‘simple’ complex filter). The
> way we usually tackle this is by creating a ‘bug’ out of this (or rather an
> issue) on our bugzilla.fcdonders.nl issue-tracking system to make an
> action list and to keep track of who’s doing what.
>
> Best wishes,
> Jan-Mathijs
>
>
> On Jul 15, 2014, at 7:26 PM, Max Cantor <mcantor at umich.edu> wrote:
>
> In the main beamformer tutorial (
> http://fieldtrip.fcdonders.nl/tutorial/beamformer), the common filter is
> computed as follows:
>
> cfg.grid.filter = sourceAll.avg.filter;
> sourcePre_con  = ft_sourceanalysis(cfg, freqPre );
> sourcePost_con = ft_sourceanalysis(cfg, freqPost);
>
> However, in the separate common filters example script (
> http://fieldtrip.fcdonders.nl/example/common_filters_in_beamforming), the
> common filter is much more complex.
>
> I've created working versions of both common filters for DICS, as well as
> a working version of the 'simple' common filter for LCMV. I have a version
> of the 'complex' common filter that should work, but it usually chews up my
> computer's RAM (I have 16gb) and crashes matlab. The DICS one is also slow,
> but not so bad that it crashes. However, I couldn't imagine running it on
> all my datasets and being able to do any stats on the data without my
> computer crashing.
>
> Before I post the code to see if maybe there is something wrong with it
> causing the memory overloads, I was wondering if anyone could explain to me
> what exactly the differences between the two methods are, and if it is even
> necessary for me to get the more complex common filter working? The simple
> common filters seem to work fine, but they could be affecting the data in
> ways that are not obvious, so I want to make sure.
>
> As always, thank you Fieldtrippers
>
> --
> Max Cantor
> Lab Manager
> Computational Neurolinguistics Lab
> University of Michigan
>  _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
> Jan-Mathijs Schoffelen, MD PhD
>
> Donders Institute for Brain, Cognition and Behaviour,
> Centre for Cognitive Neuroimaging,
> Radboud University Nijmegen, The Netherlands
>
> Max Planck Institute for Psycholinguistics,
> Nijmegen, The Netherlands
>
> J.Schoffelen at donders.ru.nl
> Telephone: +31-24-3614793
>
> http://www.hettaligebrein.nl
>
>
> _______________________________________________
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>



-- 
Max Cantor
Lab Manager
Computational Neurolinguistics Lab
University of Michigan
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