[FieldTrip] efficiently handling multiple events within a trial

[Anne Urai]

I've been writing my own trialfun but so far I've gotten by with a separate
one for eg. stimulus- and response locked, which seems rather inefficient
indeed.  Thanks for the suggestion of using ft_selectdata, didn't know that
one yet!

Anne


Anne Urai


On 19 May 2014 09:20, Eelke Spaak <eelke.spaak at donders.ru.nl> wrote:

> Hi Anne,
>
> What I usually do is segment my data initially such that a "trial" in
> the data structure really corresponds to a logical trial in the
> experiment. So, in your case, it would contain the data for both
> stimuli and the maintenance period.
>
> I assume you are writing your own trialfun for this (if not, see
>
> http://fieldtrip.fcdonders.nl/example/making_your_own_trialfun_for_conditional_trial_definition
> ).
> In your trialfun, you can specify arbitrary metadata for every trial
> by adding extra columns to the output trl-matrix. The 4th and higher
> columns in the trl matrix will end up in data.trialinfo in the output
> data. This trialinfo field is kept throughout your analysis pipeline,
> as long as the data still contains trials. You could, for instance,
> store the time index of the response as the 4th column of your trl,
> the time index of the feedback onset as the 5th, etc. I always make
> sure that at least a condition identifier and a reaction time (if
> applicable) appear the trialinfo field.
>
> Once this information is present in data.trialinfo, you can use
> ft_selectdata and ft_redefinetrial to select the appropriate trials
> and (if necessary) shift the time axis, respectively.
>
> Hope that helps,
> Best,
> Eelke
>
> On 18 May 2014 19:41,  <anne.urai at gmail.com> wrote:
> > Hi Fieldtrippers,
> >
> > I have a design in which every trial has several events of interest (two
> > stimuli with a maintenance period in between, response and feedback) -
> all
> > of which I’d like to analyse at some point. I started by drafting my
> > pipeline separately for stimulus-, response- and feedback-locked trial
> > definitions, but this leads me to do the artefact rejection and ICA
> multiple
> > times for each subject. I would prefer to reject whole trials and not use
> > any of the events in there, rather than eg. use the response for some and
> > the stimulus for others.
> >
> > I was wondering if you have any advice on how to best store multiple
> events
> > in one trial (which would be, say, 12 seconds long, and have 4 different
> > evens in it, at times that would also need to be stored). Would it work
> > better to (1) make one big trialfun and store the onset and offset of
> each
> > of those events in the trl matrix, or (2) have several trl matrices for
> each
> > event and redefine the trials based on this trl matrix after I applied
> some
> > other analyses? For example, it would be nice to run ft_freqanalysis
> once on
> > the whole trial, and then redefine which part of the trial I’m
> interested in
> > for plotting.
> >
> > Thanks for your thoughts on this!
> >
> > Best,
> >
> > ---
> > Anne E. Urai, MSc
> > PhD student | Institut für Neurophysiologie und Pathophysiologie
> > Universitätsklinikum Hamburg-Eppendorf
> > Martinistrasse 52, 20246 Hamburg, Germany
> >
> >
> >
> >
> >
> >
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