[FieldTrip] ft_prepare_leadfield: no electrodes or gradiometers specified

Eelke Spaak eelke.spaak at donders.ru.nl
Tue Oct 4 16:10:56 CEST 2011


Hi Kevin,

Your data structure (the original one, the result from a call to
ft_preprocessing) should have a .elec field already in it; I think you
should be able to just copy that .elec field to whatever it is you are
giving as input to ft_prepare_leadfield (e.g. freq.elec = data.elec;).

(Disclaimer: I do not have any experience with ft_prepare_leadfield
myself, but have heard of stuff related to this, so if I'm mistaken
please correct me :) )

Best,
Eelke

2011/10/4 Stephen Politzer-Ahles <politzerahless at gmail.com>:
> Kevin,
>
> I'm not familiar with ft_prepare_leadfield, but in the past when I had
> similar electrode-related error messages I was able to resolve it by first
> running
>
> elec = ft_read_sens(filename, ...)
>
> and then adding elec to the data structure. I believe the file I used for
> ft_read_sens was a layout file I exported from EEGLAB.
>
> Best,
> Steve Politzer-Ahles
>
>> Message: 3
>> Date: Tue, 04 Oct 2011 14:51:29 +0200
>> From: Kevin Lam <K.Lam at donders.ru.nl>
>> To: fieldtrip at donders.ru.nl
>> Subject: [FieldTrip] ft_prepare_leadfield: no electrodes or
>>        gradiometers    specified
>> Message-ID: <4E8B0151.4060109 at donders.ru.nl>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Hi all,
>>
>> I recorded EEG using BrainVision Recorder and have analyzed the data
>> (ERP and TFR). Now, I would like to determine the source of the TFR
>> effects. (I've been following, more or less, this procedure:
>> http://fieldtrip.fcdonders.nl/tutorial/beamformer)
>>
>> I'm having trouble executing ft_prepare_leadfield. Here's what I've done
>> in the preceding steps, per participant:
>>  - ft_redefinetrial to specify the time of interest for each of the two
>> conditions
>>  - ft_freqanalysis to calculate CSD matrix per the freq of interest for
>> each condition
>>  - ft_volumesegment using 'spm' for coordsys
>>  - ft_prepare_headmodel using 'singlesphere' for method
>>
>> Now, when I attempt ft_prepare_leadfield, I get an error saying 'no
>> electrodes or gradiometers specified'. I understand what the function
>> needs, but I don't have the input file it's asking for. It's not the
>> .lay file - I gave this a try.
>>
>> Please advise. Thanks in advance!
>>
>> Regards,
>> Kevin
>>
>>
>> ------------------------------
>>
>> Message: 4
>> Date: Tue, 4 Oct 2011 15:05:10 +0200
>> From: Davide Rivolta <drivolta81 at gmail.com>
>> To: Email discussion list for the FieldTrip project
>>        <fieldtrip at donders.ru.nl>
>> Subject: [FieldTrip] power line filter
>> Message-ID:
>>
>>  <CAMkcSw7oubKNktYkJz8_V3ObcP=zbEruxRn3YLA2yBkCRhgFRg at mail.gmail.com>
>> Content-Type: text/plain; charset="iso-8859-1"
>>
>> Dear all,
>>
>> I am trying to get rid of the power line noise. I use the dftfilter as
>> indicated on the website.
>>
>> This works very well for most of the subjects. However, for some of them,
>> I
>> still get the noise.
>>
>> My trials have a different lenght: between 500 ms until 3 seconds.
>>
>> This is the script I used.
>>
>>
>>  filterfreqs = [49:1:51 99:1:101 149:1:151];
>>
>>    cfg.dftfilter      =  'yes';
>>    cfg.dftfreq      = filterfreqs;
>>    cfg.padding    = 10;
>>
>>    dataprepro_syn = ft_preprocessing(cfg);
>>
>>
>> The pad of 10 is the same as another already published study that used the
>> same task.
>>
>>
>> Attached is a picture of the problem (blu is baseline, red is stimulus).
>> This is the result of multitepering (dpss).
>>
>>
>> Thanks for your help,
>>
>> Davide
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>>
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>> End of fieldtrip Digest, Vol 11, Issue 3
>> ****************************************
>
>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://www.linguistics.ku.edu/
>
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