[FieldTrip] reading in and segmenting Netstation data

[van Hoogmoed, Anne H - (annevanhoogmoed)]

Dear all,



I'm using Fieldtrip to analyze my Netstation data. The problem is that the segmented data (incl triggers) are shifted in Fieldtrip as compared to the Netstation analysis.

I've checked several things:

- The events are the same in Netstation and Fieldtrip

- The raw data look the same in both programs

- Fieldtrip produces the right trl based on the triggers.



The script I'm using is this:

cfg = [];

cfg.dataset = 'c007_raw';

cfg.continuous = 'yes';

data_eeg = ft_preprocessing(cfg);



hdr = ft_read_header('c007_raw');

event = ft_read_event('c007_raw');



cfg = [];

cfg.trialfun = 'trialfun_first_enc';

cfg_trials = ft_definetrial(cfg);

data_trials = ft_redefinetrial(cfg_trials, data_eeg);





The trialfun I'm using is this:

function [trl, event] = trialfun_first(cfg)

load event;

load hdr;





value = [event.value];

sample = [event.sample];

% determine the number of samples before and after the trigger

pretrig = -100; % = 200 ms

posttrig = 400; % = 800 ms

% for each trigger

trl = [];

for j = 1:length(event)

if (strcmp(event(1,j).value, '+Lrt') || strcmp(event(1,j).value, '+OOt')) || strcmp(event(1,j).value, '+SOt')

trlbegin = event(1,j).sample + pretrig;

trlend = event(1,j).sample + posttrig;

offset = pretrig;

newtrl = [trlbegin trlend offset];

trl = [trl; newtrl];

end

j = j + 1;

end





Does anyone know what I'm doing wrong here?



Thank you very much for your help!



Kind regards,



Anne



Anne van Hoogmoed

Down Syndrome Research Group

Department of Psychology, University of Arizona
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