weird artifact with Ganglion (touching the laptop)
First of all, thanks all for the support community here.
I have a few questions about the signals I am getting from my new Ganglion board. I have finally managed to set it up and followed all the instructions and videos in the website.
Here are 3 tests that give the expected results:
The eye blink test
The closed eye test (increase in the alpha wave) -- note those recordings are from my forehead
and finally, the "teeth grinding" test mentioned in one of the videos:
OK. Then I noticed that when I leave my hands off my MacBook pro I notice a little signal with the onset of either touching or leaving my hands off my laptop. Here is the "taping" test where I continually touch my laptop like finger tapping test:
This does not happen when I touch any other laptop or other metal or anything else. I am most definitely sure this is an artifact (and a huge one as I am planning to run a few experiments that require using the mousepad).
BTW: I am using both D_G and REF upper pins (connected to my right and left earlobes) in addition to upper channels 1 and 2 (with switches set to DOWN positions).
Is there anything I can do to investigate this and probably solve it?
Comments
Fahd, can you clarify? I do not see this artifact in your other images. What is different? Are you saying that when you remove your hands from the laptop, this noise occurs?
Does this laptop have a 3 pin power plug: ground and 2 pins of DC? Have you tried this test on other laptops? Some 3 pin power plugs connect the laptop case to the wall outlet ground pin. If you use an 3 to 2 pin adapter (drops the ground pin) -- some ground oddities disappear.
Regards, William
Yes,** last image is the only one that shows what I mean by the touch artifact**. First 3 images are only an evidence that my EEG works as expected (nothing wrong with set-up or things like that) — sorry if that was confusing.
And yes my laptop has 3 pin power plug (similar to this power cord from Amazon
https://www.amazon.com/dp/B005E2XT0W/ref=cm_sw_r_cp_api_i_3zX-Db695TS6C) so this might be the issue here.
I will find another 2-pin adopter and see if the issue persists.
Thanks a lot for the help.
Or does it occur when you TOUCH the laptop. A ground issue would show up when touching, not when removing hands. The first 3 images you were touching?
Please try this on another laptop.
If your laptop has direct AC power, that could be another noise issue. When I referred to 3 pin power, most laptops I'm aware of have a power adapter that converts AC to DC. And some adapters bring the ground wire to the laptop frame.
It shows both when I touch the laptop or remove my hands from the laptop. The third image above is what happens when I repeatedly touch the laptop very fast.
I will try another laptop if using another adapter doesn’t resolve the issue. Will update this thread about any progress.
Note that EMF electromagnetic fields from mains frequencies, can travel several feet before dissipating. Be sure that your EEG equipment, both amplifier and electrodes, are spaced away from wall outlets, power supplies, floor/wall conduits, extension cords, etc.
Here are some more tests: it does look like the power plug is the fault here. Even with using a two-pin power adapter I still see the artifact. However, the artifact completely disappears when I unplug the power cord (and only rely on battery) or when I unplug the electrodes from my body.
Try with another laptop. What type were these tests done with?
The three conductors in the wall outlet are Neutral, Hot, and Ground. Even though your adapter removed Ground, Neutral still has a connection to Ground at the power panel service entry. Both Neutral and Hot have large amplitude of mains frequency EMF emitting potential. It's possible that the AC / DC power brick you are using, somehow allows Neutral related EMFs to get into the laptop via the DC leads. Generally this is a defect in the design or wiring of the laptop / supply. Should improve with another model of laptop.