EOG sensors & software

jetsterjetster
edited March 2015 in Electrodes
Hi, I'm new to OpenBCI...first post.

Has any one done any measurement of noise and signal quality with dry (active) electrodes? I noticed that all of the videos showing OpenBCI always see use wet electrodes. I'm looking to develop an ambulatory sleep monitoring solution that uses dry electrodes...wet electrodes just aren't practical for home use on an ongoing basis.

I seem to recall a list of signals that could be collected with this solution. I saw lots of different signals listed (somewhere...maybe on TI 1299 Data sheet) but EOG was explicitly not mentioned. Can you get EOG readings with this solution?


Regards,
Jet

Comments

  • adminadmin
    Can you describe where the electrodes need to be placed and what to look for when looking for EOG?
  • jetsterjetster
    EOG (Electrooculagraphy) EOG sensors are placed at the outer edge of each eye to detect movement of the eye. Detecting eye movement (e.g., rolling motion, eye fluttering) is one of the key physiological signals need to distinguish between various sleep stages....which is what my application is all about.

    Does that help?

    Jet
  • adminadmin
    yes, i think for sure we will be able to distinguish between sleep stages with active dry electrodes.
  • jetsterjetster
    Admin,
    I don't want to sound rude but since you don't have a profile I have no way of determining what qualifications you have to be able to respond my question. I need some context. Who are you and what experience do you have to draw your conclusion? Are you the IT guy? Or do you have real hands on experience testing with this solution and knowledge of the system?

    What is your basis for your response? (e.g., you've actually tested with dry electrodes and you know the noise levels? or you are just guessing?, You have specific experience with sleep monitoring and what it takes to distinguish various sleep stages?, etc. )

    What about the EOG question (e.g., no mention of EOG as one of the physiological signals that it is designed to record...why is that?).

    Thanks,
    Jet



  • chipaudettechipaudette
    Hi,

    I can't answer your question regarding dry active electrodes. I've only used wet passive electrodes.

    Regarding EOG, I have used OpenBCI to explore EOG. If you're interested, you can check out: <a href="http://eeghacker.blogspot.com/2013/11/measuring-eog-with-my-eeg-setup.html">http://eeghacker.blogspot.com/2013/11/measuring-eog-with-my-eeg-setup.html</a>;

    Thanks for your interest!

    Chip
  • jetsterjetster
    Chip, thanks for the reply...I reviewed your blog entry on EOG. Interesting stuff...just curious did you ever run your test with the sensors to test left and right eye movement?

    Dry electrodes are much more convenient than wet electrodes. Active electrodes help overcome the high impedance levels between the skin and dry electrode.

    Thanks again,
    Jet
  • chipaudettechipaudette
    Hi Jet,

    That one experiment with EOG is all that I've done. I haven't done both eyes simultaneously. If you give it a true, post some results!

    Re: active electrodes...oh, I'm definitely familiar with them. We're very much looking forward to trying some active electrodes with OpenBCI...we just haven't yet. There aren't nearly as many inexpensive ones available.

    I did get a couple of active electrodes from Olimex ($9 each) when I was playing with OpenEEG. I didn't like the Olimex electrodes at all. They're just a flat PCB, not cup-shaped like a proper electrodes. They're also huge. Totally impractical, IMHO.

    So, moving forward, I'm definitely interested in both wet-active and dry-active electrodes. Given the lack of cheap off-the-shelf options, we'll probably have to build some here. Maybe a cheap passive electrode with a TL072 and some hot glue?!?

    Chip
  • adminadmin
    Hi Jet,

    I'm Joel, one of the founders of OpenBCI, and very intimate with the workings of our system and we've tested numerous types of electrodes in our lab. Active dry electrodes work very well with the OpenBCI system. I have good data from testing ECG and EMG and EEG.
    We have not done an EOG specific test, but I am sure that we will get good results when we do.

    ps, the forum software is abit crude. I will set up my own personal account after the kickstarter madness passes!
  • jetsterjetster
    Joel, thanks for the reply! If you are getting good EMG signals I would assume that you could also get good EMG signals but since the TI spec explicitly failed to mention EOG I wasn't sure. I'm looking forward to getting a board when it becomes available.

    Regards,
    Jet
  • dirkjotdirkjot

    <blockquote>"the TI spec explicitly failed to mention EOG "</blockquote>

    Don't worry about that, electrically EOG is just EEG applied to another spot. However, for fine grained EOG measurement you need a near DC amp, and I we have to see how the openbci/TI will deliver in that regard. Given Chip's blog post http://eeghacker.blogspot.nl/2013/11/measuring-eog-with-my-eeg-setup.html, it sounds like we can get down to 0.2Hz at least and it shows great EOG signals.

    HTH,
    Dirk
  • wjcroftwjcroft Mount Shasta, CA
    Dirk, yes the ADS1299 is DC coupled. There is NO hardware high pass filtering of low frequency signals. This is also a requirement for InfraLow Frequency (ILF) EEG applications, which go down to .001 Hz. (~ 16 minute cycle time!) See http://www.eeginfo.com/newsletter/?p=654 and http://www.lightfield.com/nf.htm

    You DO want to use a high pass digital filter at say .1 Hz if you are doing conventional EEG or EOG; this removes the DC baseline. Chip does this in his applications.
  • ratlabguyratlabguy
    Jetster, I'd just like to clear up a few things for future reference.

    "Dry" and "Active" are completely independent technologies. Dry typically just means no gel (although some mfrs use it to mean no classic gel, but the sensor may still be self-moistening). This is of course an ideal goal for most folks since it makes setting up a whole lot easier.
    However b/c the impedance of dry skin is very high, at least on the outermost surface, the native SNR of EEG is very low... and you need a nice high impedance amp to match it.
    The ADS1299 itself is kind of agnostic to what the connection impedance is, but the rest of the package should be matched.

    Now "active" vs "passive" refers really to where in the DAQ chain the first pre-amp is. In classic "passive" systems it is part of the system board that the electrode wires input to. E.g. electrode-> wire-> preamp. "Active" refers to moving that pre-amp closer to the electrode, or even on top of it. An example is Biosemi's system. This gives great SNR b/c you aren't amplifying any EMI picked up by the wires (an antenna effect). However this is expensive to implement (b/c it means an amp on every lead) and these days w/ highly portable systems, the wires are pretty short so it's not as big of a problem.
    W/ the lower SNR of dry electrodes for EEG, the boost from active amps helps but isn't a requirement. There are other systems using the ADS1299 and older 1298 that use non-active dry electrodes.

    Just wanted to be sure that was clear.

    Oh and re: EOG vs EEG vs EMG.... as far as the DAQ goes... its all just voltage. The only difference is what you're trying to measure ;-)
  • wjcroftwjcroft Mount Shasta, CA
    Moved the question below from @johanping (and @NeuroJoe ) over to this existing thread on EOG.

    ----

    So I was using Chip Audette's EOG setup (http://eeghacker.blogspot.com/2013/11/measuring-eog-with-my-eeg-setup.html)  to measure eye movements and was having a little trouble with MATLAB processing code.

    What I ultimately want to do is to use the EOG input as an output to the Arduino that controls a robotic eye so that I can essentially make the eye mimic human eye movements in real time. (Like what Chip did with EEG data and LED/Hex Bug). 

    I am at a very basic level with all of this (have no prior programming experience, except for some very simple things with Arduino), and was having trouble translating from his posts http://eeghacker.blogspot.com/2014/06/controlling-hex-bug-with-my-brain-waves.html. 

    I am wondering if there is a way to very simply get the EOG data input and then transform it into simple if else statements in Arduino - for instance, if one electrode above the human eye reaches some threshold voltage then the arduino will activate the eye to move upward, and the same with an electrode below the human eye. I apologize if this is a somewhat simplistic view of the scenario, but I have to believe there is a simple way to code this action?

    Johanping
  • wjcroftwjcroft Mount Shasta, CA
    edited March 2015
    @johanping & @NeuroJoe ,

    Try some searching around on Google. This came out immediately on the top of the list:

    https://www.researchgate.net/profile/Manuel_Merino_Monge/publication/224193917_A_Method_of_EOG_Signal_Processing_to_Detect_the_Direction_of_Eye_Movements/links/0a85e52e7b6a7629e1000000.pdf

    Seems like exactly what you are "looking for".  :-)

    Generally easiest way to do this is to put the detection algorithm on your laptop. NOT on an Arduino (OpenBCI or separate Arduino.) Then for your motor drive, use a SEPARATE Arduino on it's own serial port. You will send commands such as L R U D to that system and it will move the eyeball.

    William

    PS even more stuff here: https://www.google.com/search?q=eog+detect+eye+motion
  • abhinavjainabhinavjain Singapore
    I tired measuring EOG using the Ganglion board. While I was able to detect eye movement in both differential and EEG mode, the baseline was shifting back to zero and was not able to detect any low frequency movement on the OpenBCI GUI.

    Can someone please highlight how I can measure lower frequency (such as EOG in REM sleep) using ganglion board?

    Thanks, 

  • wjcroftwjcroft Mount Shasta, CA
    Abhinav, hi.

    re: baseline drifting back to zero.

    Ganglion has a built in high pass filter at approximately .3 hz.  Unlike Cyton, which does not have built in high pass. So you might have to just make do with that Ganglion limitation. You do get the EOG movements, just no long baseline reference.

    Also see,


    Regards,

    William

  • abhinavjainabhinavjain Singapore
    Hi William,

    Thanks for the prompt reply. I see, I most likely will have to purchase a cyton board. I just bought the board couple of days ago and looks like I'll have to spend close to 500$ now :-(.

    Will try to play around with it and see if ganglion.
  • wjcroftwjcroft Mount Shasta, CA
    Can't you detect REM eye movements, even with the Ganglion limitations? Why would you need 'absolute' eye positioning? Isn't the movement alone enough to trigger your REM detector? Perhaps with some averaging or thresholds?
  • abhinavjainabhinavjain Singapore
    Unfortunately, in a typical REM sleep one loop of eye movement may take up to 10 sec to complete. Thus, 0.3 Hz might be already too high.

    I am checking the paper you've shared in your previous message it could be something which can help us. I'll dig more into it and see if something can be done.

    Thanks for your help thus far,

    -AJ
  • MaymounahMaymounah Jordan

    @wjcroft said:
    Abhinav, hi.

    re: baseline drifting back to zero.

    Ganglion has a built in high pass filter at approximately .3 hz.  Unlike Cyton, which does not have built in high pass. So you might have to just make do with that Ganglion limitation. You do get the EOG movements, just no long baseline reference.

    Also see,

    http://openbci.com/forum/index.php?p=/discussion/1257/ganglion-high-pass-filter-problem

    Regards,

    William

    @wjcroft
    I purchased the ganglion board last month to acquire EOG signal and use it to classify eye movements, the required BPF is (0.02-40)Hz, so I wonder if the problem of the built-in High pass [email protected] exists in the latest produced ganglion boards?

  • MaymounahMaymounah Jordan
    edited December 2021

    @wjcroft @retiutut @evaesteban
    I've just been confirmed by the OpenBCI's sales that this problem is still available (ganglion has a built-in high pass filter @0.3 Hz). Unfortunately, this board will not work on my signal as most of the signal information while eye fixation is beyond 0.3 Hz. Any way to solve this problem? for example, can I add capacitors or resistors to the hardware?
    regards,
    Maymounah

  • wjcroftwjcroft Mount Shasta, CA

    @Maymounah said:
    I've just been confirmed by the OpenBCI's sales that this problem is still available (ganglion has a built-in high pass filter @0.3 Hz). Unfortunately, this board will not work on my signal as most of the signal information while eye fixation is beyond [below] 0.3 Hz. Any way to solve this problem? for example, can I add capacitors or resistors to the hardware?

    No, you cannot change the .3 Hz Ganglion highpass, it is built into the amplifier front end. And secondarily Ganglion uses a compression algorithm that is tailored to EEG signals that do not have large millivolt swings.

    On the other hand, Cyton does not have this limitation and supports arbitrary DC level changes. So possibly you could attempt to upgrade your Ganglion to Cyton. But that would be up to OpenBCI Sales.

    Regards, William

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