Experience with OpenBCI Gel-Free Electrodes and VR
Hello Everyone,
I am a PhD student working on passive BCIs and VR. Wanted to get one of these gel-free electrode bundles: https://shop.openbci.com/products/all-in-one-gelfree-electrode-cap-bundle from OpenBCI for my VR project since their specifications perfectly match our requirement. I have tested prior electrodes like Emotiv with VR headsets like HTC Vive and the Meta Quest but those are quite uncomfortable for the user unlike the gelled counterparts. Wanted to know if anyone had the experience of using the gel-free electrodes with the VR HMDs before taking a decision.
Any info on their experience with VR is helpful. Alternatively, any suggestions on alternative EEG headsets would also be welcome
Thank You!
Comments
Hi Srikrbha,
I suggest you consider how many channels you will need and the 10-20 (scalp) locations. If your VR headset has headband(s), which most do, then there may be 'overlap' between what scalp locations you are trying access, and where the headband rests. Sites that overlap are likely to be both uncomfortable (extra pressure on hard surfaces), and distort the EEG (movement / muscle artifacts will be larger).
William
Hi William,
I am using an HTC Vive Pro Headset and a Meta Quest. I have previously used a gelled electrode from Brain Products (livamp-acticap32) but these weren't that uncomfortable. Wanted to compare it with the gel-free one from OpenBCI since we had a separate saline-based (gel-free) electrode from Emotiv Epoc series but this was incredibly uncomfortable to the users. Wanted to make sure that these aren't too uncomfortable for longer experiments for participants to use.
Thanks You,
Best Regards,
Srikrishna
It could depend on what degree the electrode / holders size (large or small) and hardness / depth. My impression is that the gel free cap electrodes / holders have both significant depth and hardness. Without a VR headset, these extend above the cap with no issues. With a headset pressing down, electrode extension from cap will contact the headset straps.
https://www.greenteksensor.com/products/eeg-caps/gt-cap-gelfree-s3/
Hmm, I'm pretty sure these caps are from Greentek Sensor. Yet the link above shows different electrode holders than the cap on the Shop page,
https://shop.openbci.com/products/gelfree-bci-cap-kit
Possibly Greentek has simplified the electrode holder geometry. Nevertheless, both types of cap have significant extension of the hard plastic assemblies, ABOVE the flat surface of the cap fabric.
Not seeing the Shop cap on the Greentek site. Perhaps the Shop is showing the S4 cap, and their own page shows the older S3 model. Looking closely at the Shop page, the cap there has TWO tags on the edge, one from Greentek, and the other shows OpenBCI logo. So I'm guessing now the Shop version may be a custom model designed for OpenBCI??
https://www.greenteksensor.com/products/eeg-caps/
Mentioning Kris @khofstadter. Kris do you understand the differences between Greentek S3 and S4 versions? What do you think the Shop (and Docs) page shows? I believe you have the S3.
https://shop.openbci.com/products/gelfree-bci-cap-kit
https://docs.openbci.com/AddOns/Headwear/GelfreeElectrodeCap/
Here is Kris's very first post on the Greentek saline cap, from 2017, 2018.
https://openbci.com/forum/index.php?p=/discussion/1663/greentek-gelfree-s-eeg-cap
Hello. Thanks William.
I only tried the S1 and the S3.
My S3 looks different than the one in the OpenBCI shop. I think one of the main differences is that the S3 cap has the cable loom integrated. On the shop picture, the cable loom is seperate from the cap. This, I guess means that the shop has the S4 version. This seperation could be very useful if you need to replace one part only. But maybe it has other benefits too.
I have been happy with the S3. I bought my caps straight from Greentek and customer service was really good.
Anything else, please let me know.
k
Kris, thanks. Yeah I have no idea why Greentek does not have listing on their own site for the non-loom version of the cap.
Would you have any comments for the original post on this thread, by @srikrbha, asking if you think the Greentek saline caps would work with VR headsets. It looks doubtful to me if the VR headset has an over-the-head strap(s) system.
William
Thanks @wjcroft. Let me know your experience @khofstadter on using Greentek saline caps with VR headsets. Once again, thanks for all the help both of you.
Hi Srikrbha, I'm sorry, but I have no experience with VR headsets. I imagine you might need to consider not only comfort when using both EEG and VR headsets but also how the VR headset is strapped on the head. For example, it might not be a good idea if some EEG electrodes are pressed down by the VR headset while others aren't. Perhaps there's a VR headset that doesn't have a strap in the middle pushing down on Fz, Cz, Pz, etc. However, this also depends on which locations on the head you need to measure brainwaves from. I am sure you thought about all of this, just wanted to bring it up.
P.S. What's the research question btw.?
Thanks @khofstadter. We are working on passive BCIs that change the VR environment based on parameters like workload, stress, engagement inferred from EEG.
We won't be using the middle areas (Fz, Pz, Oz, Cz, etc.). But this was good to know. As long as it doesn't cause clashes with the forehead areas and the VR headset it should be fine.
This other important thing to note is the difference between the Greentek Saline S3 headset that @khofstadter is using, and the Greentek (S4 or 'custom' made for OpenBCI) headset listed on the Shop page. With Kris' headset, the upward facing hard plastic electrode holder projections are closer to the scalp. With the S4, they project farther upward. From photos it might a half inch high or more. So even if the middle area 10-20 sites are not used because of the VR head strap, the pressure on the hard plastic holders may be irritating.
Thus what I am trying to say is that S3 and S4 may differ in how comfortable they are with downward pressure from a VR central strap head band.
Thanks @wjcroft, thats important and good to know!