[FieldTrip] Help with definetrial for EGI .mff file

Mon Apr 24 14:41:56 CEST 2023

apologies for the multiple postings: i made a typo in my previous message: the line that reads ’ft_trialfun_general’, should of course read ’ft_trialfun_show’.

Best wishes,
Jan-Mathijs

On 24 Apr 2023, at 14:31, Jan Mathijs Schoffelen <janmathijs.schoffelen at donders.ru.nl<mailto:janmathijs.schoffelen at donders.ru.nl>> wrote:

Hi Mathew,

Thanks for the additional information.

Note that ft_definetrial/ft_trialfun_general will only work according to expectation if eventtype and eventvalue are correctly specified. Their correct specification depends on how the events and their values are represented in the data file. This is something I don’t know for the format you use, but it could be that ’stim’ should read ’Stim’, and/or that the event values ahould be numeric( e.g., [1 2 3 4], rather than {’01’ ’02’ ’03’ ’04’}. If you are unsure about how values/types should be defined for your data, you should use the ft_trialfun_show function:

datapath='E:\FT\OFP1.mff'
EGIformat= 'egi_mff_v3'
cfg = [];
cfg.dataset = datapath;
cfg.dataformat = EGIformat
cfg.headerformat = EGIformat
cfg.trialfun = 'ft_trialfun_general’;
cfg=ft_definetrial(cfg);

This will give you some feedback on the screen, which you can use for a properly formatted call to ft_definetrial with trialfun = ‘ft_trialfun_general’

Good luck,
Jan-Mathijs

On 22 Apr 2023, at 06:33, Varghese Mathew 1881002 <varghese.mathew at res.christuniversity.in<mailto:varghese.mathew at res.christuniversity.in>> wrote:

Thank you so much for the response.
I have tried using ft_trialfun_general in the following code
datapath='E:\FT\OFP1.mff'
EGIformat= 'egi_mff_v3'
cfg = [];
cfg.dataset = datapath;
cfg.dataformat = EGIformat
cfg.headerformat = EGIformat
cfg.trialdef.eventtype = 'stim';
cfg.trialdef.prestim = 1;
cfg.trialdef.poststim =1;
cfg.trialdef.eventvalue = {'01''02''03''04'};
cfg.trialfun = 'ft_trialfun_general';
cfg = ft_definetrial(cfg)

I am getting a following response

Error using ft_definetrial
no trials were defined, see FT_DEFINETRIAL for help

This made me think if I should change the trialfun_general. Is there something I have missed and also is there any standard format to define trials on Netstation files (.mff)?

Thank you again for the response.

Sincerely
Varghese Mathew

On Wed, Apr 19, 2023 at 11:12 PM Schoffelen, J.M. (Jan Mathijs) via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:
Hi Mathew,

I am a bit surprised that you think that you need to adjust the ft_trialfun_general. The idea is that this function is quite generic, and given the scenario that you sketch, you probably don’t need to change any fieldtrip function. The partial error that you report is difficult to evaluate, since it’s only partial. Right now it’s just random guessing as to what might be going on. The error looks as if MATLAB tries to access a structure’s field called headerfile, but for some reason in does not exist in the struct that it is evaluating.

for instance, if you define on the matlab command line the following struct:

x.a = 1;

and then query x.b, you get the error you report.

What is the full error stack, i.e. which line in which matlab function is throwing the error?  And what is the code that you try to execute (i.e. the specification of the cfg, and the fieldtrip function you are calling).

Good luck,
Jan-Mathijs

On 19 Apr 2023, at 16:27, Varghese Mathew 1881002 via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Hi
I am doing analysis on Netstation EGI .mff file using Fieldtrip, I have tried using .mff file directly and after converting to EDF. However, I am getting error in defining trials. Mostly I get an error message  Unrecognized field name "headerfile"  .
I would like to know how to go about this in EDF or .mff format.
It will also be helpful if someone can help with how to modify ft_trialfun_general for .mff file as well.
I am pasting the code I used, below.
cfg=[]
cfg.dataset = 'E:\FT\OP17.mff';
cfg.dataformat = 'egi_mff_v3'
cfg.headerformat = 'egi_mff_v3'
cfg.trialdef.eventtype = 'stim';
cfg.trialdef.prestim = 1;
cfg.trialdef.poststim =1;
cfg.trialdef.eventvalue = {'01''02''03''04'};
cfg.trialfun = 'ft_trialfun_general_stimmod';
cfg = ft_definetrial(cfg)

For modifying trialfun_general

function [trl, event] = ft_trialfun_general_stimmod(cfg)
event = ft_read_event(cfg.dataset, 'headerformat', 'egi_mff_v3');
% Find trigger values
trigger = [event(strcmp('stim', {event.type})).value]';
% Note: Replace 'STI101' with the label of the trigger channel that
% contains the trigger values for your data
% Define trial segments
trl = [];
for j = 1:length(trigger)
if any(trigger(j) == [01 02 03 04])
trlbegin = event(j).sample;
trlend = trlbegin + 1000; % define trial length as 1 second
offset = 0; % no offset
newtrl = [trlbegin trlend offset trigger(j)];
trl = [trl; newtrl];
end
end
Please help with the issue, as I am trying to pick up analysis using Fieldtrip and I do not have a coding background.
Looking forward for a response,

Sincerely
--
Varghese Mathew

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Varghese Mathew
Mobile No. 9535395896

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