[FieldTrip] Problem with FT_DEFINETRIAL

[Ivano Triggiani]

Dear Jarmo,

Filedtrip needs a definition of segments of interest. For example reading a trigger channel or something else to cut the EEG recording into trials. If I have understood what you want to do is to get an average of general EEG (for example resting state EEG closed eyes). But you have to indicate which average you want to obtain, for example you can tell fieldtrip to divide EEG into epochs of 3 seconds and then to make an average of all of them.
What you wrote is the request of an average, but you are not specifing of what.
Fof example you can write a trial function that provides a trl matrix, i.e.:
0 3 0

3 6 0
6 9 0
9 12 0
12 13 0
...

where first column is the start sample in seconds (you have to multiply it for sample rate), the second column is the end sample and the third is the offset (in this case is always zero), or look at 
http://fieldtrip.fcdonders.nl/tutorial/preprocessing#use_your_own_function_for_trial_selection

best wishes,
Ivano



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and another to the multitude,
without finally getting bewildered 
as to which one is true."


Nathaniel Hawthorne


________________________________
 Da: "fieldtrip-request at donders.ru.nl" <fieldtrip-request at donders.ru.nl>
A: fieldtrip at donders.ru.nl 
Inviato: Lunedì 26 Marzo 2012 12:00
Oggetto: fieldtrip Digest, Vol 16, Issue 33
 
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Today's Topics:

   1. Re: Problem with FT_DEFINETRIAL (Stephen Politzer-Ahles)


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Message: 1
Date: Sun, 25 Mar 2012 12:11:28 +0200
From: Stephen Politzer-Ahles <politzerahless at gmail.com>
To: fieldtrip at donders.ru.nl
Subject: Re: [FieldTrip] Problem with FT_DEFINETRIAL
Message-ID:
    <CAJT2k__mFC_FxgG2ggt9hJHhNp59DEZgXFMLAQ1BNoErGFJyfg at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Hello Jarmo,

I haven't tried importing Brain Vision files into FieldTrip myself, but
based on the code you sent it looks like the problem may be that you're
missing cfg.trialdef.eventvalue (which is used to tell FieldTrip which
triggers to select), cfg.trialdef.prestim, and cfg.trialdef.poststim . See
the example at
http://fieldtrip.fcdonders.nl/tutorial/preprocessing#reading_and_preprocessing_the_interesting_trials.

If what you are trying to do is import all trials from all triggers in the
file, I think you have to define your own "trialfun" function to do that
(although I haven't tried this myself so I'm not sure).
http://fieldtrip.fcdonders.nl/reference/ft_definetrial has some more
information.

Best,
Steve Politzer-Ahles
University of Kansas


Message: 1
> Date: Thu, 22 Mar 2012 17:14:46 +0100 (CET)
> From: Jarmo Kontinen <Jarmo.Kontinen at ruhr-uni-bochum.de>
> To: <fieldtrip at donders.ru.nl>
> Subject: [FieldTrip] Problem with FT_DEFINETRIAL
> Message-ID:
>        <
> permail-201203221614466509e8c700002494-Jarmo.Kontinen at msgid.mail.ruhr-uni-bochum.de
> >
>
> Content-Type: text/plain; charset=us-ascii
>
> Dear all,
> I am trying to import EEG subject averages into Field Trip. The files are
> exported with the Brainvision Analyzer in binary form
> :subject10_konPro2002.dat and subject10_konPro2002.vhdr.
> I have a problem with turning the data into the Field Trip data-structure.
> I
> am following instructions given on this forum on one similar post. What I
> have
> tried is the following:
>
> cfg=[];
> cfg.trialdef.eventtype='average'
> cfg.dataset='subject10_konPro2002.dat'
>
>  cfg=ft_definetrial(cfg);
>
> Warning: no trialfun was specified, using trialfun_general
> > In ft_definetrial at 123
> evaluating trialfunction 'trialfun_general'
> reading the events from 'subject10_konPro2002.vhdr'
> ??? Error using ==> ft_definetrial at 176
> no trials were defined, see FT_DEFINETRIAL for help
>
> I am grateful for all the help.
> Thanks,
> Jarmo Kontinen
>
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