connecting electrodes with the FRI 19 channel headband
Dreaming_Geek
Atlanta
I just bought the 32 bit R&D kit with daisy chain.
The headband should be here in a couple of days.
19-Channel EEG Headband
Am having a hard time finding the docs that tell me how ALL the electrodes connect to the pins and the headset.
Please help a n00b?
Comments
Or are you asking how to use the gold cup electrodes with this headband? That is not as straightforward. As the holes in the headband are designed to fit the dry sensor combs, not regular cup / paste electrodes. Perhaps Karl @KZurn or Brooks @jbzurn will jump in here.
With the dry sensor cables, those are plugged into the touchproof adaptors you receive with the R&D kit. You are the one who chooses how you want to map your 10-20 locations to the channels. Most BCI setups use ear lobes for the reference, and those are frequently linked with a Y cable. Your Bias lead can go anywhere on the head; the Electro-cap places it at AFz. A midline location is good as it injects the anti-noise signal equally to both sides of the head.
http://fri-fl-shop.com/product-category/electrode/packages/
You can connect any channel to any 10-20 site, it's your choice. You can do a lot of good stuff with just 8 or less channels. See the OpenViBE speller tutorial. Note that without the daisy, you get 250 sps, but adding the daisy drops you to 125 sps, which is a consideration in some cases. Many neurofeedback protocols just use 2 or 4 channels.
I don't know anyone doing source localization with OpenBCI yet, but in that case 16 channels would give decent coverage, still not full 19 channel. I think the mix of the comb vs. cone electrodes in the packages allows you to work with most head/hair types. Since this is very dependent on the hair coverage of the person you are working with.
Another way to use the dry electrodes is with the g.tec g.GAMMAcap, mentioned on some other threads, use the search box. Or with the BrainNet elastic 10-20 point mesh. The material used in the FRI straps is Velcro One-Wrap, which you can buy in 12 foot rolls.
http://eeghacker.blogspot.com/
As far as lining up with the OpenBCI_GUI head map, just touch / wiggle each electrode one at a time and see what lights up. That's one correspondence you can use, but it was chosen arbitrarily.
In most BCI software, the channel to 10-20 site mapping is handled in one of the setup dialogs. So you can map it however you like. In OpenBCI_GUI, that map change dialog is not yet present, so just one layout was chosen.
There are EEG data stream file standards, such as EDF, BDF, XDF -- that carry a channel mapping table as part of the format. The free EDFBrowser package allows you to import from CSV files (such as our GUI creates).
http://openbci.com/forum/index.php?p=/discussion/556/default-map-of-channel-numbers-to-10-20-sites
There is a similar map for channels 9-16. You can figure this out yourself by touching electrodes and see what lights up on the OpenBCI_GUI head map.
Is 'R' meant to refer to 'Reference'? Generally the Reference is going to one or both ear lobes. And the Bias can go to any of the unused 10-20 or 10-10 sites.
It would be a beneficial to integrate elements of this diagram into the tutorial docs on the OpenBCI_GUI. Hoping that someone in the lab could look into this. Rodrigo @Rceballos98 has made such additions in the past.
The SRB closest to the board is SRB2, and it is the default reference.
I'll look for a space to add this into the documentation. Maybe even having it in the getting started guide next to electrode placements.