reuse of beamformer filters

jan-mathijs schoffelen j.schoffelen at PSY.GLA.AC.UK
Wed Sep 17 15:35:36 CEST 2008


Dear Michael,

If I recall correctly what you would like to do, I would suggest one  
of the following two paths:

first possibility:
-perform sourceanalysis with cfg.keepfilter = 'yes' and with an  
averaged covariance as input
-append source.avg.filter to cfg.grid for a second round of  
sourcenalysis, but now with the condition-specific covariances as input.
you might want to check it in the code, but I am quite sure that if  
the configuration already contains filters, it will use these on the  
input
covariance
-this will give you two source-structures, one for the baseline and  
one for the task condition.

second possibility:
-use sourcestatistics and create a 'first-level' stat for each  
subject, using as cfg.statistic = 'diff'. This will just take the  
difference between
task and baseline.

Hopefully this helps,

Best,
JM

On Sep 16, 2008, at 3:56 PM, Vladimir Litvak wrote:

> 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.

----------------------------------
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.



More information about the fieldtrip mailing list