importing and displaying BrainVision format files

Working with OpenViBE signal processing scenarios and doing scenario/BCI design
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KJeffrey
Posts: 74
Joined: Wed Jul 20, 2022 6:47 pm

importing and displaying BrainVision format files

Post by KJeffrey »

This is my first forum post. I hope I am placing it in the correct place. Here is my situation:

I have a 28 subject EEG dataset collected using NeuroScan hardware, saved in their CNT format. Using EEGlab I converted this set into BrainVision format (.dat, .vhrd, .vmrk) format. I then used the BrainVision Format file reader box in OpenViBE to open the BV format files. When I try to display them, though, I get flat lines. I do not see where I can control the display scale. I need to verify the data looks OK before proceeding with my next steps.

I want to use this dataset to train an SVM classifier in OpenViBE and make sure I can get it working satisfactorily before collecting our own EEG data using the BV LiveAmp system we have purchased recently for this purpose.

I have gone through some of the tutorial material and can successfully load example .OV files and run the demos with the EEG data in them. Might I have to convert the BV format files to .OV file format before I can do that?

This is a critical pathway in our project now.

-Jeff Eriksen

Thomas
Posts: 210
Joined: Wed Mar 04, 2020 3:38 pm

Re: importing and displaying BrainVision format files

Post by Thomas »

Hi Jeff,

You should be able to read the BrainVision format with OpenViBE using the BrainVision Format File Reader.

You can change scale settings by double-clicking on the SignalDisplay box to access its settings. You can also change them when the scenario is playing by clicking on the magnifier at the top of the SignalDisplay window.

However, the SignalDisplay box should adapt to your signal, so you might just have flat lines.
Can you double check your vhdr file in EEGLab, to check the data is not flat ?

Feel free to share a sample of you vhdr data if you want me to have a look as well.

Cheers,
Thomas

KJeffrey
Posts: 74
Joined: Wed Jul 20, 2022 6:47 pm

Re: importing and displaying BrainVision format files

Post by KJeffrey »

Hi Thomas,

Well, now I noticed the messages, and they say that "only multiplexed data is supported. So, the BrainVision data is considered multiplexed? Might it work if I transposed the time and channel dimensions?

-Jeff

Thomas
Posts: 210
Joined: Wed Mar 04, 2020 3:38 pm

Re: importing and displaying BrainVision format files

Post by Thomas »

Hi Jeff,

The .vhdr file (that you can open in a text editor) contains a DataOrientation field. From what I found online, its value can be VECTORISED or MULTIPLEXED.

OpenViBE only supports the MULTIPLEXED format, meaning: "The data for all channels are written sequentially in one line for one sampling point in time. The next line contains the data for all channels for the next sampling point in time."

If the DataOrientation of your .vhdr file is "VECTORISED", then all the data points for channel one appear first in the file, followed by all the data points for channel two, etc.

Can you confirm that the DataOrientation in your .vhdr file is set to VECTORISED ?

Indeed, if you know how to transpose the data in the .eeg file and update the DataOrientation field in the .vhdr file, then you should be able to read it with OpenViBE.
Maybe that's an option you can set with EEGLab when converting your data.

Hope this helps, and let us know how you get on with this.

Cheers,
Thomas

KJeffrey
Posts: 74
Joined: Wed Jul 20, 2022 6:47 pm

Re: importing and displaying BrainVision format files

Post by KJeffrey »

I see that the data is vectorized. So either have to
1. get the people responsible for the EEGlab bva-io plugin to modify it to output multiplexed, or
2. get OpenViBE to modify the BrainVisino import to read in vectorized

Data is naturally collected multiplexed, so it is beyond me why the BrnVis plug-in would be written to output it vectorized.

I will start with (1) now.

-Jeff

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