Two questions to understanding the signal processing and top

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Galsungen
Posts: 1
Joined: Tue Sep 09, 2014 12:18 pm

Two questions to understanding the signal processing and top

Post by Galsungen »

Hello,

I'm using the Emotiv EPOC (the old one) with OpenVibe. I'm looking about activities in differents part of the brain when you do differents kind of things. It's more an explorary matter.

First I'm using one DSP shown in the tutorial on the OpenVibe website [lien]. I had some pictures (videos) of the brain.Then I try to link the topographic box directly to the Acquisition signal. I can observe two, really different, pictures of the brain. The one without any DSP don't really change, no matter what is the activity. I'd like to understand why. If anyone could help me about it.

Image

Image
here three different pictures in illustration.

I haven't any knowledge in signal processing and it's quite difficult for me to understand why i can't see fluctuation on the original signal. the scenario is available here (xml).

The temporal filter is on Band Pass 16-24.
The DSP is : x*x

This signal processing is it the right one or another mathematical formula could be more relevant ?

Another interrogation is about which frequency is the most accurate to see which part of the brain is working, activating ? I was thinking about the Beta part, from 16 to 31 Hz but in this exemple it's stop at 24 Hz.

Can Alpha (8 Hz - 15 Hz) and Gamma band pass could be relevant to ?

Thanks, in advance, for your time and answers :)

Aravind
Posts: 8
Joined: Wed Oct 14, 2015 2:56 pm

Re: Two questions to understanding the signal processing and

Post by Aravind »

Hi,

You can try to observe different activities like alpha, beta, etc. if you are just exploring the activities of the brain. For example, if you are trying to observe signals pertaining to meditation/relaxation then you should be looking for the alpha waves in the signal. Any measurement starts with an objective as to what you would like to measure, and based on that you would have to locates the different electrode positions, the frequency bands, etc. In the relaxation example once you close your eyes, there is an increase in power in the alpha band;signals recorded from the occipital regions like electrodes, O1, O2, Oz etc.

To view these signals, you should first filter them in the particular band, like for alpha - 8Hz to 12Hz, so this will be the settings of the temporal filter block. In the simple DSP box, x*x simply means you are computing the energy of the signal. So if you used a signal average block following the simple DSP, then this would mean you are measuring power in a particular band of frequency. Therefore this block can be used for further processing and decision making.

As such, to just view the activities, you could use signal display, and power spectrum display to see the alpha activity. The raw signal wouldn't affect much and doesn't provide much information, the activities are more prominent in the filtered signal.

Hope this was helpful!
All the Best

Regards
Aravind R

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