SSVEP with EPOC

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ArturS
Posts: 3
Joined: Tue Jun 02, 2015 12:23 pm

SSVEP with EPOC

Post by ArturS »

Hello,
I'm testing my custom made flickering graphics (done in After Effects) using OpenVibe and EPOC headset. Basically, I'm using one computer to display the graphics and the other PC is running OpenVibe with EPOC connected through the opnevibe acquisition server. I set up a simple scenario where I can see both raw and filtered signals. For the filtered part of the signal I'm using temporal filter, windowing function, time based epoching and then display. But I can't see any changes in the signal when shifting my view to flickers. Could please someone point me to some method/scenario
where I could set up the EPOC and OpenVibe in such way that I could detect at least 1 flickering frequency at a time. Is there any way to display signal peaks (say signal peaking at 6.3 Hz) with amplitude on Y axis and frequencies on X axis.
Thanks in advance for any help or guidance.
Artur

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

Re: SSVEP with EPOC

Post by jtlindgren »

Hello Artur,

sometimes the SSVEP effects can be weak in the EEG. Especially the EPOC electrodes are not placed optimally for this; I've heard sometimes people try a trick of turning the headset around to place more electrodes on top of the occipital lobes.

The box you're looking for is likely the power spectrum display, used after FFT transform box. You can alternatively make a frequency specific bandpass-filter and square the result to get a kind of 'power'.

You also may need to average the squared signal (power) for a while of stimulation to get a cleaner picture. Probably nonsquared averaging is not a good idea due to canceling.


Happy hacking,
Jussi

ArturS
Posts: 3
Joined: Tue Jun 02, 2015 12:23 pm

Re: SSVEP with EPOC

Post by ArturS »

Hello Jussi,
Thanks for your reply.
I will try to follow your suggestions and let you know if I got anything interesting.

Artur

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