reuse of beamformer filters

Vladimir Litvak v.litvak at ION.UCL.AC.UK
Tue Sep 16 15:56:11 CEST 2008


Hi,

I don't use sourcestatistics myself so I can't get to the bottom of
your problem, perhaps Robert or JM should try. The point is just that
you can compute filters from any data and then use them on any other
data. I don't know at what stage the baseline correction is done in
your case. I usually just get the raw output and then process in in
any way I like.

Best,

Vladimir

On Tue, Sep 16, 2008 at 2:03 PM, Michael Wibral <michael.wibral at web.de> wrote:
> Dear Vladimir,
>
> thanks for directing me to the appendix of the beamformer tutorial. My problem is indeed related but not quite the same. What I would like to do with these data later is to compare between two groups. I suspect some differences in their baselines. Hence, I would not like to work with source statistics (or relative power change values for that matter) but with raw power differences (i.e. task-baseline). Then I'd like to compare these raw power differences between the two groups. If I compare the two groups statistically using second level stats on t-values or relative changes, differences could be due to baseline differences, instead of task related absolute changes. Therefore I would like to compute the filters and keep them, but do not want to perform sourcestatististics in in each single subject, just source analysis.
>
> But maybe this is simply a bit exotic. I will also look a bit into the possibilities of sourcestatistics; whether I can actually get my desired difference output w/o stats (there should be a raweffect with each subject after sourcestats, shouldn't it. I could then use this raweffect as an input to the secondlevel sourcestats by copying it over to the correct field...).
>
> Best Regards,
> Michael
>
>
>> -----Urspr√ľngliche Nachricht-----
>> Von: "Vladimir Litvak" <v.litvak at ION.UCL.AC.UK>
>> Gesendet: 15.09.08 20:12:40
>> An: FIELDTRIP at NIC.SURFNET.NL
>> Betreff: Re: [FIELDTRIP] reuse of beamformer filters
>
>
>> Hi Michael,
>>
>> Look in the beamforming tutorial at:
>> http://www2.ru.nl/fcdonders/fieldtrip/doku.php?id=fieldtrip:documentation:tutorial:beamformer
>> in the Appendix. The option you need is cfg.keepfilter. I think what
>> is done there is more or less what you need.
>>
>> Best,
>>
>> Vladimir
>>
>>
>> On Mon, Sep 15, 2008 at 5:47 PM, Michael Wibral
>> <wibral at bic.uni-frankfurt.de> wrote:
>> > Dear Listusers,
>> >
>> > I'd like to reuse filters computed for an average covariance matrix from two conditions for the subsequent source images of each condition, so that statistics will later on not be influenced by differences in SNR that change the filter computation. Does anybody know how to do this efficiently in sourceanalysis?
>> > I thought there was an option like cfg.hasfilters='yes'or so  but obviously I was wrong :-). I also looked for something similar in source descriptives, but couldn't find anything.
>> >
>> >
>> >
>> >
>> > Any help appreciated,
>> > Michael Wibral
>> >
>> >
>> > ----------------------------------
>> > The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
>> >
>>
>> ----------------------------------
>> The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
>>
>
>
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.



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