Cyton vs. Ganglion for EEG measurements
Hello together,
I am working on a fun EEG demo for undergrad students with the following set up:
- Electrodes: Headband with dry comb electrode over the visual centre and dry flat electrodes on the forehead
- Software: I use the OpenBCI GUI with the spectrogram widget
- Effect I am showing:1. eye blinks as noise in the forehead electrodes, 2. alpha waves with closed eyes over visual centre and alpha-blocking when opening eyes
I used the Cyton and the Ganglion to test this set up each with their USB Dongle. I noticed that with the Cyton the effects are much clearer visible. Can this be due to differences in gain? I noticed with a little less gain I have better results with the Cyton. With the Ganglion the gain cannot be changed right?
Can you give more insights into the differences of Cyton and Ganglion for EEG measurements. What measures can I take to improve the results with the Ganglion as I want to use the Ganglion for future student projects.
Thanks a lot in advance!
Best, Louisa
Comments
Hi Louisa, I'm asking some of our hardware engineers to visit this thread and offer suggestions.
William
Louisa, here is one suggestion you can try:
The amplifier INPUT impedance of the Ganglion differs from that of the Cyton. So that means Ganglion is more sensitive to skin impedance than Cyton. And the dry electrode skin contact accentuates this difference.
One thing you can try is to slightly moisten the skin surface under the dry electrodes. This will decrease skin-electrode impedance and slightly amplify the signal level. You could also try either gel or paste based electrodes.
There are also saline based electrodes that are a combination of silver chloride with an absorbent pad soaked with saline solution. So no cleanup needed as with gel or paste.
https://shop.openbci.com/products/gelfree-bci-cap-kit
[there are also other types of saline electrode systems]
Still asking our engineers to contribute to this thread.
William
Louisa, here is another suggestion by an engineering staff member, Tharun (and Pyotr and myself). View this Community post below by Pyotr where he shows the normal comb electrodes you have, but threaded inside is a thin sponge material in a spiral. This is then wetted with water to increase the conductivity. If you go this route you can avoid the saline solution, as that might damage the silver chloride coating of the comb tips. Scroll down to section 2 of the post showing the electrode setup.
https://openbci.com/community/mind-controlled-robot-openbci-mindaffectbci-maqueen-v2/
His sponges shown in this image are actually A BIT too deep. You want the sponge material at the comb end to be just level with the comb tips. That way the moistened comb tips are directly in contact with the scalp. With the image as shown, the sponge will separate the comb tips from the scalp because they protrude somewhat beyond the tip.
Mentioning Pyotr, @dream4future and @little_snow.
Hello William, Tharun and Pyotr,
thanks a lot for your support!
Trying wet electrodes would have been my next step. I worked with the gold cups and the paste before but like you said it is always a bit of a mess especially in hair and therefore not really feasible in normal lectures. So I will definitely try your tip with the sponge. Great idea, that I did not know yet. It sounds like a promising- and also mess-free - solution.
Best, Louisa
Louisa, great.
If you are using the velcro band to hold the flat and comb electrodes, you can adjust the tightness of the band, even without the water. This will increase the electrode pressure on the skin and slightly reduce impedance. But take care not to become so tight as to be painful.
William
Thanks, William!