EEGLAB Biosig toolbox: problem importing markers correclty from .vmrk file

Hello fellows!

I am doing EEG analysis using the EEGLAB toolbox for treating data from BRAINVISION acquisition software. The BRAINVISION software outputs 3 files: '.eeg' - the continuous data - '.vhdr' a header file annd finally a '.vmrk' triggers markers file.

In order to import everything in EEGLAB, I use the BIOSIG importing tool in EEGLAB as such (eeglab1.png):

An then I save my dataset using file > save current dataset as.

Now we get to the issue. My .vmrk file looks like this (vmrk.png):

with the first relevant marker being the 4th one, 'S 11'

The problem is that this vmrk file is not imported correctly in eeglab via BIOSIG, and looks like this (eeglab2.png and eeglab3.png):

As you can observe the latency and duration are imported correclty, but the triggers denomination (1, 1, 11, 12, 13, etc...) are not, and particularly my trigger '11', which should be at position 4, is shifted to position 140, and hence all my triggers are shifted. Of course, since there are only 410 triggers - because my original .vmrk file contains only 410 triggers positions - , this shifting causes any additionnal triggers beyond position 410 to be ignored, meaning that additionnally to the shifting, mroe than half my triggers are missing.

I tried to use either older or most recent versions of biosig in order to see if that changed, but it doesn't help, the problem remains.

Any idea on how to fix this issue?

Thank you and cheers,

Fred

Answer 1

[Bastian Schledde]

Dear Fred,

On behalf of the Brain Products Scientific Support I would like to recommend using the bva-io extension that you can download from the EEGLAB Extension page (https://sccn.ucsd.edu/wiki/EEGLAB_Extensions). We are not aware of this issue with BIOSIG but have no reported issues using the bva-io plugin which is the dedicated import/export option for EEGLAB.

With this extension you can import files in the native BrainVision data format (.eeg, .vhdr, .vmrk) via File > Import Data > Using EEGLAB functions and plugins > From Vis. Rec. .vhdr File.

If you have further questions to the BrainVision data format or BrainVision Analyzer, please contact us at [e-mail]

With best regards,

Bastian

Brain Products Scientific Support

[Yuting]

Dear Bastian,

I am quite intreseted in relationship among three files. From what I learned, the .eeg file contains all raw data file, while the .vhdr file contain only meta infromation. Given this, I am wondering why importing .vhdr file alone is sufficient for data analysis? Why don't we import .eeg file directly?

Thank you for your time and patience!

Best regards,

Yuting

[Michael]

Dear Yuting,

The three files that make up a dataset in BrainVision data format are internally linked so that the data (.eeg) and marker (.vmrk) files can also be accessed accordingly. Effectively, the information from all three files is loaded. The header file is usually accessed first as this provides the data characteristics and dimensions of the data matrix that need to be known in order to load the data values from the .eeg file.

If you have further questions about our data format or BrainVision Analyzer, please contact us at [e-mail].

Best regards,

Michael

Brain Products Scientific Support