Cannot reproduce closed eye alpha signal

jupiterjupiter US
edited October 2020 in Cyton

Hello, I'm eager to get started hacking with my mark IV + cyton with dry comb electrodes electrodes, but unfortunately I'm off to a frustrating start. For a few days now I have been consistently unable to reproduce the closed eye alpha band peak in the frequency spectrum.

I am able to produce blink (pos. 1 and 2) and jaw clench (all pos.) EMG artifacts. I've measured dry impedances at 800-2400kOhm (down to 300-400 with wet hair tried out of desperation, though I don't know if this is good for electrode life), but no luck in producing a signal. When recording 20 second videos, first 10 seconds eyes open, last 10 seconds eyes closed, there is no noticeable difference in amplitude distributions across the frequency range. Same issue with all 8 electrodes active. I've attached a few screenshots and welcome any suggestions. Thanks!

Dry hair, classic gain

Dry hair, body gain

Wet hair, classic gain

Impedance values, dry hair

Comments

  • retiututretiutut Louisiana, USA
    edited October 2020

    When recording 20 second videos, first 10 seconds eyes open, last 10 seconds eyes closed, there is no noticeable difference in amplitude distributions across the frequency range.

    I would be more patient and look at Fp1 and Fp2. Spectrogram will clearly show this change over time when electrodes are connected and there are no additional artefacts. Key word here is patience, in that trials of 20 seconds are like a "fast food" approach.

    In this Community post, you can see a screenshot I took of GUI v5 after sustained "meditation" with my eyes closed: https://openbci.com/community/gui-v5-release/

  • wjcroftwjcroft Mount Shasta, CA

    Richard, thanks.

    Jupiter, hi.

    Please try your test on another subject. People differ in their amounts of eyes closed alpha production, and some produce much less than others. This is still 'normal'. The sites of highest alpha production (in general) are in the rear: O1, O2, P3, Pz, P4.

    William

  • retiututretiutut Louisiana, USA
    edited October 2020

    The sites of highest alpha production (in general) are in the rear: O1, O2, P3, Pz, P4.

    William is correct. To be more specific about the Spectrogram widget, you will notice a "Channels" button in the top left of the widget. Clicking this will hide/show the Channel Select bar for certain widgets (TimeSeries, BandPower, Spectrogram). The data displayed is an average of the selected channels, with a default configuration of Right vs Left Hemisphere. It might be helpful to select only the channels you are interested in.

    Hope this helps,
    RW

  • jupiterjupiter US

    Thanks for the suggestions. Was worried I wasn't getting good S/N. I'll try for longer, and get a friend to try.
    I appreciate your efforts to democratize EEG.

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