I bought "OpenBCI 32-bit Board Kit" and follow the "Tutorials" to make the test. Everytime, the maximum EEG Amplitude is always around 2 Hz, not 8~10Hz(Alpha) in FFT plot.
Afliu, hi. Your image did not come through, it appears to link to a folder and not a file. Perhaps your permissions are not set to allow viewing. Message says:
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Can you try again? So you have an electrode at say O1, and ground and reference at opposite ears. But you see no change in the signal when eyes are opened vs. closed. Is that correct? Does the signal plot change when you put your finger on the electrode? Can you try the other tests in the tutorial as far as ECG and EMG.
Alpha band is generally from 8 to 12 hz, peak at 10 hz. But peak location can change depending on the individual.
Actually, I did see the changes in the signal when eyes are opened vs. closed.
However, I was confused that in the FFT Plot, the peak EEG Amplitude is around 2Hz. Based on my understanding, 2Hz should be Delta rhythm and it begins to appear in stage 3 sleep. When I was running the test, I am not in sleepy, so just did not understand why the peak is around 2Hz, not Alpha thythm 8~12 Hz.
If you want some more background on how delta is involved in much more than just sleep, see this paper by Knyasev,
EEG delta oscillations as a correlate of basic homeostatic and motivational processes Gennady G. Knyazev
"It is suggested that dynamic coordination at a timescale of hundreds of milliseconds (such as delta oscillation) may be essential for optimization of distributed representations in the brain, whereas patterns of synchronous local interactions may be coordinated dynamically on a faster timescale."
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However, another point to consider is that motion artifacts of your head or body, eye-blinks, can appear to be delta; and as the cables move around they cause slow shifts that mimic delta. See if the FFT below 4 hz quiets down as you are absolutely still.
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Add the snapshot above.
My bad for the wrong link, here is correct one:
https://drive.google.com/file/d/0By4X4xbJLYIjUFkyMUlUaFdETTQ/view?pli=1
Actually, I did see the changes in the signal when eyes are opened vs. closed.
However, I was confused that in the FFT Plot, the peak EEG Amplitude is around 2Hz. Based on my understanding, 2Hz should be Delta rhythm and it begins to appear in stage 3 sleep. When I was running the test, I am not in sleepy, so just did not understand why the peak is around 2Hz, not Alpha thythm 8~12 Hz.
Any comments are appreciated!
Thanks,
This is typical, see the last image in the tutorial, strong delta is present there as well.
http://docs.openbci.com/tutorials/01-GettingStarted#getting-started-w-openbci-vi-check-out-your-bodys-electrical-signals
If you want some more background on how delta is involved in much more than just sleep, see this paper by Knyasev,
Gennady G. Knyazev
----
However, another point to consider is that motion artifacts of your head or body, eye-blinks, can appear to be delta; and as the cables move around they cause slow shifts that mimic delta. See if the FFT below 4 hz quiets down as you are absolutely still.
Regards, William
Thanks for the quick response and documents link, it is definitely helpful for me to understand more about EEG. Appreciated!!