[Eeglablist] BDF import - reference problem

[Andrew Hill]

I'm not sure you can skip the ref on import in a BDF file (without losing 40 dB or S/N), but choosing EXG1 EXG2 or 65 66 or whatever your mastoids/ears are will give you a trace like Bradley suggests, e.g. the ears will sum to zero, if you leave the ref channels in.  

Instead of choosing linked ears on import, if you pick a single channel (e.g. Pz or 30) then you will simply see a flat line in the scrolling plot for the date.

FWIW I've not had any of the problems you describe when importing BDFs, though recently I've been first converting them to EDF using BioSemi's "converter" tool (free download on their site).

Remember that MATLAB is pretty poor at memory management - once you start getting memory errors, restart MATLAB, or you will keep getting errors that might not otherwise happen.

Best,
Andrew

On Jun 20, 2011, at 3:31 PM, Bradley Voytek wrote:

> If you're uncertain, look at the timecourse of the linked mastoids. If
> it did reference correctly, the whole timecourse should be zero.
> 
> You can also skip the automatic reference step during import, and
> instead reference immediately after importing your data.
> 
> ::brad
> 
> On Sun, Jun 19, 2011 at 04:28, mirek <3mirek at gmail.com> wrote:
>> Hello,
>> 
>> As a novice in EEGLAB (on the way from BrainAnalyzer) I'm trying to
>> import Biosemi BDF file. According to the manual which advises to
>> indicate reference electrodes in the import popup window, I'm doing so.
>> However, after the import, the main EEGLAB window states "Reference:
>> unknown". When loking at the logs in the Matlab console, it seems that
>> the referencing took place:
>> 
>> Reading data file header...
>> Warning SOPEN: number of event onset (TYP=0) and event offset (TYP=8000)
>> differ (0,3)
>> Warning SOPEN: EVENT ONSET later than EVENT OFFSET
>> We highly recommend that you choose a reference channel IF these are
>> Biosemi data
>> (e.g., a mastoid or other channel). Otherwise the data will lose 40 dB
>> of SNR!
>> Warning SOPEN: number of event onset (TYP=0) and event offset (TYP=8000)
>> differ (0,3)
>> Warning SOPEN: EVENT ONSET later than EVENT OFFSET
>> Reading data in BDF format...
>> eeg_checkset note: upper time limit (xmax) adjusted so
>> (xmax-xmin)*srate+1 = number of frames
>> Importing data events...
>> eeg_checkset note: creating the original event table (EEG.urevent)
>> Re-referencing...
>> Warning: channel 40 is now zeroed (but still present in the data)
>> eeg_checkset note: re-creating the original event table (EEG.urevent)
>> Done.
>> Re-referencing data
>> Done.
>> 
>> I was trying to use single electrode as reference as well as multiple
>> (linked mastoid), but still got "Reference: unknown" message.
>> 
>> I can use "Re-reference" command afterward, but it only works when I use
>> single electrode. Then the message changes into e.g. "Reference: EXG8".
>> When "Re-referencing" to multiple electrodes, again "Reference: unknown"
>> is shown.
>> 
>> Would somebody help me to solve this problem...?
>> 
>> Thanks,
>> Mirek
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