[Eeglablist] import BDF into EEGLab

[Andrew Hill]

Hi Alberto,

Yes, you need to reference to (any) channel on import, as the BDF file has a DC offset with a huge range, and without a reference this gets dramatically truncated (you lose relative sensitivity).  I typically import with a reference of Pz (near the REF-CMS/DRL locations) and then reference to linked ears or average after import (and after I identify and replace any problematic channels).

I do think an BDF->EDF conversion / export is a good idea before importing into EEGLab..  this is how I approach ERP studies with BDF files - using the "Converter" supplied by BioSemi, with default settings (e.g. the high pass filter at 0.13 Hz is sufficient to remove the DC offset).  You could also just try filtering at 0.5 Hz after import, or try removing the average of each epoch after epoching.. using something like EEG.data = detrend(EEG.data) or EEG.data=EEG.data-repmat(mean(EEG.data,2),[1 EEG.pnts 1])

If you aren't doing ERP studies, but instead working with continuous EEG, you can probably get away with hipassing at 1Hz or higher on the imported BDF file directly.  The ERPs are "smeared" (in time) when you high-pass too "high", but ICA shouldn't be as affected.  

Best,
Andrew

On Nov 11, 2013, at 2:17 AM, Alberto Inuggi <alberto.inuggi at gmail.com> wrote:

> dear Sirs
> 
> concerning the necessity to specify a reference while importing BDF into EEGLAB, do I have to do it exactly when I import it ? or con i reference later ?
> my final aim is to apply a common average reference
> 
> can I do this:
> 
> EEG = pop_biosig(input_file_name, 'importannot','off');
> EEG = pop_reref(EEG, [reference],'keepref','on');
> 
> or i strictly HAVE to do this:
> 
> EEG = pop_biosig(input_file_name, 'importannot','off', 'ref', XX);
> EEG = pop_reref(EEG, [reference],'keepref','on');
> 
> Another question, is it advisable to first convert BDF to EDF with the Biosemi converter this in order to (as written in another list post) "avoid using an aggressive 1hz filter against the BDF offset"
> 
> 
> thanks in advance
> regards
> Alberto
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