[Eeglablist] About electrode locations (Easycap) and topoplot

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Oct 16 15:49:46 PDT 2014

Dear Ramon,

He says EasyCap file is not compatible with EEGLAB channel import. Could
you check it?

Meanwhile, Ai, if you have channels names like Fz, Cz, Pz... this naming
rule is called 'international 10-5 system' which EEGLAB can find their
default values according to Oostenveld and Praamstra (2001)'s definition.
Just confirm that all the channel names follow this 10-5 system, and import
it, and 'find locs' in 'edit-channel locations'.


On Mon, Oct 13, 2014 at 3:39 AM, AI KOUITSU <
ai-kouitsu at edu.brain.kyutech.ac.jp> wrote:

> Hello all,
>  I am a beginner, and I have some questions about how to calculate
> the electrode locations for Easycap and the topoplot() function.
> 1. As is written in this page
> http://sccn.ucsd.edu/wiki/Channel_Location_Files,
> the Easycap electrode location file seems compatible with
> eeglab-->readlocs()
> function. But the hyperlink has been invalidated.
> 2. I downloaded the Easycap electrode location file from the
> availableofficial webpage,
> http://www.easycap.de/easycap/e/downloads/electrode_sites_coordinates.htm#2
> ,
> and tried to import it by "Edit-->channel locations-->Read locations".
> When I pressed
> the "Read locations" and selected the location file, a pop-up list
> starting by
> "File format: autodetect...." appeared. But after I pressed the "OK"
> button,
> an error came out with the following messages.
> Undefined function or variable "eloc".
> Error in readlocs (line 458)
>    if isfield(eloc, 'sph_theta_besa')
> Error in pop_chanedit (line 664)
>                         [chans] = readlocs(tmpargs{:});
> Error using waitfor
> Error while evaluating uicontrol Callback
> 3. I also tried to input the XYZ-coordinates manually, but the electrode
> locations
> are a little strange that they are not on a unit spherical surface, it's
> like an
> ellipsoid surface. I am really confused, because I saw all the coordinates
> from your
> standard .loc file have the same radius (on a unit sphere).
> What should I do when construct a 2D heap map from such kind of 3D
> coordinates?
> 4. I am also wondering what algorithm you applied when topoplot. Something
> about
> Current Source Density and Surface Laplacian can be found over the
> internet,
> but write such codes seems not so easy, could you give me some hints or
> advice
> of how draw a 2D head map?
> Thank you!
> Best regards,
> Guangyi Ai
> =======================================================
> Graduate School of Life Science and Systems Engineering
> Dept. of Brain Science and Engineering
> Guangyi Ai
> Email: ai-kouitsu at edu.brain.kyutech.ac.jp
> =======================================================
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Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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