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

[kousik sarathy]

Hey Katrin,

It seems to me that Max's suggestion would suffice. But you seem to be
looking for something else. Could you elaborate a little bit as to what you
need?

--
Regards,
Kousik Sarathy, S



On Tue, May 27, 2014 at 8:30 PM, KatrinH Heimann <katrinheimann at gmail.com>wrote:

> 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
>>>
>>> _______________________________________________
>>> fieldtrip mailing list
>>> 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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