[Eeglablist] A few beginner questions (biosemi data)

[Makoto Miyakoshi]

Dear Omar,

> 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).


No, the re-reference process should be the same.



> 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?


Yes, I agree with you. That should be a metadata bug. I'll file it for you.



> 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?

Yes. However, if you will use ICA, you want to re-reference after ICA so
that you can avoid rank reduction for ICA.

Makoto

2014-03-22 8:59 GMT-07:00 Omar Mian <omian88 at gmail.com>:

> 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?
>
>
>
> Thanks
>
>
>
> Omar
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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