[FieldTrip] In BIOSEMI data format, baseline of each data much differ depending on channels

[中村一太]

Hi All,

Now I try to read BIOSEMI data (.bdf format, 64ch) by using "ft_preprocessing", but I have one trouble.
Baseline of each data much differ depending on channels. So, now I use cfg.demean as below script.

cfg.trialdef.prestim        = 0.5; % in seconds
cfg.trialdef.poststim       = 1; % in seconds
cfg = ft_definetrial(cfg);
cfg.demean='yes';
cfg.baselinewindow = [-0.1 0];
cfg.channel = {'Fp1' 'AF7' 'AF3' 'F1' 'F3' 'F5' 'F7' 'FT9' 'FT7' 'FC5' 'FC3' 'FC1' 'C1' 'C3' 'C5' 'T7' 'TP7'...
  'CP5' 'CP3' 'CP1' 'P1' 'P3' 'P5' 'P7' 'P9' 'PO7' 'PO3' 'O1' 'Iz' 'Oz' 'POz' 'Pz' 'Fp2' 'AF8' 'AF4' 'Fz' 'F2'...
  'F4' 'F6' 'F8' 'FT10' 'FT8' 'FC6' 'FC4' 'FC2' 'FCz' 'Cz' 'C2' 'C4' 'C6' 'T8' 'TP8' 'CP6' 'CP4' 'CP2' 'CPz' 'P2'...
   'P4' 'P6' 'P8' 'P10' 'PO8' 'PO4' 'O2' 'PO9' 'PO10' };
cfd.reref=('yes');
cfg.refchannel=('all');
data = ft_preprocessing(cfg);

But, I now focused on DC shift(Slow cortical potential <0.5Hz), so, I can't use cfg.demean and I'm looking for another method to solve this problem.
Additionally, is this trouble( Baseline of each data much differ depending on channels.)  common with BIOSEMI data format ?
or is it due to our recording device?

I woud appreciate if someone could advise or comment on how bests to go about this issue.

Thanks.
Itta Nakamura M.D.
Kyushu-University Neuropsychiatry Department, Japan.  

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