Saving classifier output as trigger in the EEG file

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Santiago
Posts: 2
Joined: Tue Apr 05, 2016 1:09 pm

Saving classifier output as trigger in the EEG file

Post by Santiago »

Hello,

I started using OpenVibe recently, and I need some help with triggers.
I am running a simple Motor Imagery paradigm, similar to the spaceship scenario. I am using Biosemi for the EEG acquisition. Beta band power is computed on Cz, and a Sign Change Detector Box detects if the signal crosses a threshold. This box then sends a stimulation to a Matlab Scripting Box, which receives it and sends a command to an external device (robotic hand with Arduino).

I would like to have a precise marker of the moment when hand moved, and would like this marker to be saved in the EEG file for offline analysis. So I'm considering several ways of sending and storing this marker.

1/ Can I save a ''stimulation" in the EEG file using the Stream Writer? (e.g. the same way Biosemi stores triggers in a separate trigger channel). Because one option for me would be to send the stimulation from the Change Detector Box also to to Stream Writer Box directly.
1bis/ Can I use the Matlab Scripting Box to output stimulations that are then fed into the Stream Writer?
2/ I could send a trigger from Matlab through a cable to the Biosemi Acquisition Server, right before or after it sends the command to the external device. This will then be saved in the EEG file. Is there a better option?

Here is a diagram of the setup:
Image

I found this about triggers from an external application, but I don't think it is a solution for me.

Thank you very much for your help,
Santiago
Last edited by Santiago on Tue Apr 12, 2016 3:08 pm, edited 1 time in total.

nfoy
Posts: 40
Joined: Fri Nov 14, 2014 1:06 pm

Re: Saving classifier output as trigger in the EEG file

Post by nfoy »

Hello,
As far as I understand you don't need hardware trigger nor software trigger. Your Matlab box simply needs to output a stimulation that you connect to your file writer box in the designer.
Hope this helps!
Best regards

Santiago
Posts: 2
Joined: Tue Apr 05, 2016 1:09 pm

Re: Saving classifier output as trigger in the EEG file

Post by Santiago »

I wasn't sure that was possible, but yes, it makes sense. Thank you!

Another question: Is there any way of having two different stimulation inputs in the GDF or the EDF file writer? I saw it was possible with the Generic Stream Writer, but not the EDF or GDF. I would like to save the EEG signal, OV stimulations but also triggers coming from the EEG acquisition server.

I would use the .ov format but I need to do offline analysis with fieldtrip, which does not support .ov (neither does EEGLAB afaik) :(

Thank you.

EDIT: I think I found the solution: combining the two stimulation streams using the Stimulation Multiplexer box.

jtlindgren
Posts: 778
Joined: Tue Dec 04, 2012 3:53 pm
Location: INRIA Rennes, FRANCE

Re: Saving classifier output as trigger in the EEG file

Post by jtlindgren »

Yes, if the stimulation codes are distinct, the multiplexer should do the trick! Many formats don't support multiple stimulation streams (or if they do, our code doesn't...) .


Cheers,
Jussi

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