[FieldTrip] ft redefine trials: how to change trigger?

[KatrinH Heimann]

Dear Max, thanks a lot for your prompt answer. Unfortunately this is not
what I am looking for (I found an example like this in the tutorial). I
would like to change the trigger for one of the two conditions, let it be
now the response of the subject, as this is where the stimulus actually
starts... Defining two different timewindows is not enough... Can you also
help me with that? Thanks a million! Katrin


2014-05-27 18:58 GMT+02:00 Max Cantor <mcantor at umich.edu>:

> Hi Katrin,
>
> It may help to see your code, but hopefully this will help. It should be
> as simple as taking your epoched data from ft_definetrial and
> ft_preprocessing, then creating two configurations for your timewindows and
> running ft_redefinetrial.
>
> For example (from the fieldtrip tutorial, slightly simplified by me for
> explanatory purposes):
>
> ***
>
> % find the interesting segments of data
>
> cfg                             = [];
>                  % empty configuration
> cfg.dataset                 = 'Subject01.ds';
>        % name of CTF dataset
> cfg.trialdef.eventtype    = 'backpanel trigger';
> cfg.trialdef.prestim       = 1;
> cfg.trialdef.poststim     = 2;
> cfg.trialdef.eventvalue   = 3;
>           % event value of FIC
> cfg                             = ft_definetrial(cfg);
>
> % preprocess the data
>
> cfg.channel                 = {'MEG'};
> dataFIC                      = ft_preprocessing(cfg);
>
> % define time window
>
> cfg                            = [];
>
> cfg.toilim                   = [-0.5 0];
> dataPre                     = ft_redefinetrial(cfg, dataFIC);
>
> cfg.toilim                   = [0.8 1.3];
> dataPost                   = ft_redefinetrial(cfg, dataFIC);
>
> ***
>
> So if your code resembles this, you are defining in cfg.trialdef.prestim
> and cfg.trialdef.poststim a timewindow that encompasses both your baseline
> period and stimulus period, then for cfg.toilim in the ft_redefinetrial
> section you are setting one to your baseline period and the other to your
> stimulus period, and outputting them into separate variables.
>
> Hopefully this helps. Also, if you haven't done so already, I would
> strongly recommend you run through the tutorial, as it may help answer
> questions like this in the future (assuming I've properly identified the
> issue).
>
> Good luck,
>
> Max
>
>
>
>
> On Tue, May 27, 2014 at 12:10 PM, KatrinH Heimann <katrinheimann at gmail.com
> > wrote:
>
>> Dear all,
>>
>> my name is Katrin Heimann, I am phd student at the University of Parma.
>> New to Fieldtrip.
>> I am doing an EEG analysis, still in the preprocessing phase.
>> It is a within trials design. I would like to compare a baseline period
>> with an experimental condition (visual stimulus).
>>
>>  I have a trigger after a fixation cross, then a baseline period (approx
>> 1 sec) , then the period of my stimulus (1 sec- starting with a bottom
>> press (trigger)).
>>
>>  As I would like to apply the same baseline correction for both (the
>> fixationcross period)  I planned to first define my trials as long trials
>> including the timewindows of baseline and the stimulus period, applying
>> filter and baselinecorrection on those long pieces. However, as I do not
>> wanna do the artifact detection on the whole pieces (but seperately for
>> baseline and stimulus, to avoid that I have to throw away too many trials)
>> I would like to redefine my trials then, cutting out only baseline period
>> and only stimulus period (starting with another trigger
>> (triggervalue=resp)..
>>
>> *Unfortunately I do not understand how I can change the trigger used with
>> ft redefine trial. *
>>
>> Anybody who could give me an example how that is done?
>> Thanks a million
>> Katrin
>>
>> _______________________________________________
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>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>
>
>
> --
> Max Cantor
> Research Assistant
> Computational Neurolinguistics Lab
> University of Michigan
>
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>
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