[Eeglablist] A few beginner questions (biosemi data)

Omar Mian omian88 at gmail.com
Sat Mar 22 08:59:03 PDT 2014

I'm new to EEGLAB and EEG data processing in general. I am getting started
by working with some 40 channel Biosemi .bdf data files (32 scalp electrodes
+ 8 additional electrodes). I have a few questions that I'd appreciate
assistance with.


1) I understand it is important to specify the reference channel/s  for the
Biosemi data. But is it important to specify the reference channels during
the import stage compared to after the data have been imported? (I ask
because the import GUI points out that reference channel Indices are
required for BIOSEMI - it's just not clear to me if this is referring
specifically to the import stage). To work around the issue I raise in point
2 below, it seems to me that I'll need to reference after loading the
channel locations rather than during import.


2)  After referencing the dataset, the dataset gui displays the reference
channels correctly. However, if I subsequently update the channel locations
(using edit | channel locations, and selecting
"\eeglab13_1_1b\plugins\dipfit2.2\standard_BESA\standard-10-5-cap385.elp" as
the channel location file), the reference channels go back to "unknown". As
far as I can tell, the data array is not being affected, so is this just a
dataset metadata bug?


3) I assume it does not matter whether basic filtering for pre-processing
purposes (e.g. get rid of low frequency drifts) is done before or after
referencing. Is this correct?





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