[FieldTrip] Error with ft_artifact_threshold on a dataset with overlapping Trials

[giulio piperno]

Dear Fieldtrip Community,

my name is Giulio Piperno, and I am working as Ph.D. Student in Cognitive Neuroscience at La Sapienza University of Rome.

I am new to Fieldtrip, and I am currently using it to analyze the data of an ERP experiment. After the filtering, the segmentation, and the baseline correction,  I encounter a problem with the automatic artifact detection, using the function ft_artifact_threshold

More specifically, I receive thefollowing  error messages:

Error using ft_fetch_data (line 165)
some of the requested samples occur twice in the data and have conflicting values

Error in ft_artifact_threshold (line 183)
    dat = ft_fetch_data(data,        'header', hdr, 'begsample', trl(trlop,1), 'endsample', trl(trlop,2),
    'chanindx', chanindx, 'checkboundary', strcmp(cfg.continuous, 'no'));


I suspect the problem is related to the presence of overlapping trials.  The interval between the triggers is 550 ms, and the error message appears only when I try to take segments longer than 550 ms in the segmentation process (E.g. form 250 ms before the trigger up to 400 ms after the stimuli). If I reduce the length of the epochs, I receive no error. Unfortunatly, I need to take long segments, because I am interested in both prestimulus (around 250 ms) activity and a peak occurring around 200-400 ms after the stimulus

However the problem could be rather something related to the baseline correction step:  If I run  ft_artifact_threshold on the data before the baseline correction, I receive no error (even when I take segments with -250 400 ms interval and therefore I have overlapping trials)

I tried to insert the command cfg.allowerlap = "yes" in the preprocessing but it didn't work


Could someone tell me if there is something wrong with the cfg settings I 'am using or if I am doing something wrong at any other place? Is there a way to perform both baseline correction and automatic artifact detection on a dataset with partially overlapping trials?

Here I leave the code I am using:

%%% FILTERING %%%
cfg = [];
cfg.bpfilter = 'yes';
cfg.bpfiltord = 3 ;
cfg.bpfreq = [0.1  30];
data_cleaned_filtered = ft_preprocessing(cfg, data )


%%% SEGMENTATION %%%

filename= 'C01.cnt'

cfg = [];
cfg.dataset = filename
cfg.trialdef.eventtype  = 'trigger';
cfg.trialdef.eventvalue = 1:1:37;
cfg.trialdef.prestim    = 0.25; % in seconds
cfg.trialdef.poststim   = 0.4; % in seconds
cfg.trialfun            = 'ft_trialfun_general';
data_trl= ft_definetrial(cfg);
data_trl.trl=round(data_trl.trl)

cfg = [];
cfg.trl       = data_trl.trl;
data_segmented = ft_redefinetrial(cfg, data_cleaned_filtered);


%%%  BASELINE CORRECTION %%%

cfg          = [];
cfg.demean        = 'yes'; %
cfg.baselinewindow = [-.25 -.15];
data_baseline = ft_preprocessing(cfg, data_segmented);

%%% AUTOMATIC ARTIFACT DETECTION %%%

cfg = [];
cfg.continuous = 'no';
cfg.artfctdef.threshold.channel     = 'EEG';
cfg.artfctdef.threshold.bpfilter     = 'no';
cfg.artfctdef.threshold.max = 100; %value in uV or T, default  inf
cfg.artfctdef.threshold.min = -100; %value in uV or T, default -inf
[cfg, artifact_EEG] = ft_artifact_threshold(cfg, data_baseline);

Thanks in advance for your help!

Best Regards

Giulio Piperno
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