[FieldTrip] definetrial error

[Schoffelen, J.M. (Jan Mathijs)]

Dear René,

It is not clear what you want to do exactly, but in general you should not expect that a tutorial that was written for task based data, for instance an oddball task, works as is for any other data, in your case a clinical EEG dataset.
There are several reasons for this. First of all, an experimental dataset  typically contains markers at specified timepoints in the data, that indicate certain events happening, for instance the onset of a visual stimulus on the screen, or a button pressed by the participant. Using this event information (which is represented in a dataset specific way) the experimenter can determine which chunks of the data are interesting for further investigation. The definition of the chunks of interest is done in ft_definetrial (which is the function that throws the error), but this only works if the data aligns with the instructions that the function is given. Now, given that you input clinical EEG data in combination with an event extraction recipe (’trialfun_oddball_stimlocked') that has no relation whatsoever with any event information stored in the EEG data file, it is bound to fail.

So the question now is whether you want to learn about dipole fitting, or whether you want to learn about epilepsy data analysis, or about a combination thereof.

We don’t have a lot of teaching material about epilepsy, but a good start might be http://www.fieldtriptoolbox.org/tutorial/epilepsy/, rather than the tutorial you referred to. Note, however, that this tutorial concerns MEG data, and some parts of it are not relevant in case of EEG data. On the other hand, it might give you some handles on how this type of data can be analyzed.

Best wishes,
Jan-Mathijs




On 3 Jun 2020, at 19:37, Andrade Rey René <rene.andrade at edu.uah.es<mailto:rene.andrade at edu.uah.es>> wrote:

Dear FieldtripToolbox experts:
I am presenting myself as I am new in the community. I am a student of Medicine in University of Alcala de Henares in Madrid Spain.
I have a problem when running the dipole fitting tutorial. I have downloaded and set to path this trialfun_oddball_stimlocked.m file.

>> cfg=ft_definetrial(cfg)
evaluating trialfunction 'trialfun_oddball_stimlocked'
Warning: channels with different sampling rate not supported, selecting subset of 33 channels at 250.000000 Hz
Warning: channels with different sampling rate not supported, selecting subset of 33 channels at 250.000000 Hz
Error using ft_definetrial (line 196)
no trials were defined, see FT_DEFINETRIAL for help


I am running on Temple University Hospital TUH EEG dataset of epilepsy.

Thank you for your help in advance!
Best,
Rene Andrade.
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