[FieldTrip] Reading in .bdf files

Matt Craddock matt.craddock at uni-leipzig.de
Tue Sep 23 17:12:14 CEST 2014

Hi Ricarda,

The EXG channels are for external electrodes - typically they are used 
for things like eye movements (for example we always placed EXG1-4 at 
points around the eyes) and additional reference points (e.g. mastoids, 
earlobes). You'd need to check with whoever recorded the dataset to be 
sure which channel is which.

I have not tried to read .bdfs using fieldtrip, as i usually do a lot of 
pre-processing in eeglab and port over to fieldtrip later on, but 
subtracting the mean of each channel (DC) as well as re-referencing may 
help. BDFs have a very high dynamic range which can have some 
unfortunate side effects at times:



On 22/09/2014 15:43, Ricarda Braukmann wrote:
> Hi everyone,
> I have a question regarding reading in Biosemi .bdf files.
> I followed the example on the ft website to read in a .bdf file, and -
> although it does not give an error- , the data looks very odd. In the
> ft_databrowser for example the vertical scale is [ -178000178000 ] which
> seems very werid to me.
> I tried re-referencing the data, like in the example, using channel
> 'EXG5', but this did not help.
> Is there anyone who has experience with reading in biosemi files who
> could give me some advice?
> It would also be great if someone could explain to me what these EXG
> channels are exactly.
> I have for now turned to converting the .bdf file to .edf file (using
> the converter from www.biosemi.com/download/
> <http://www.biosemi.com/download/ToolsForRuntimeEngine861/Converter86.zip>).
> Then the data looks normal, but it created some other issues with my
> markers and I would rather not use the converted files.
> More than anything, I am very curious what is going on with the original
> file, so any help is much appreciated!
> Thanks in advance!
> Ricarda

Dr. Matt Craddock

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