[Eeglablist] Plotting scalp electrodes/topography neatly inside head outline

Arnaud Delorme arno at ucsd.edu
Wed Jan 15 18:26:39 PST 2014


Dear Pete,

You can call the topoplot and change 'headrad'. 
However, you need to remember that this is not correct representation according to the topoplot convention. Any electrode below the midline is not visible from a view from above the head. Hence it is plotted (by convention) outside the head.

Best,

Arno

On Jan 9, 2014, at 12:32 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu> wrote:

> Dear Pete,
> 
> In my experience, multiplying 0.7893 to polar radius worked (that does not mean I correct it all the time; I don't care :-). Try this code and compare topomaps. Don't forget to apply 'optimize center' before doing it (this button is on the right top of channel edit window).
> 
> %%%%%%%%%%%
>     for n=1:length(EEG.chanlocs)
>         EEG.chanlocs(1,n).radius = EEG.chanlocs(1,n).radius*0.7893
>     end
> %%%%%%%%%%%
> 
> There was a big discussion in SCCN what the head 'circle' in the topoplot should represent... generally speaking, any channels located lower than the circumference that connects Nz-eye-earholes/auriculars-Iz should show outside the circle (i.e. 'skirt'). Note that this 'interpretation' stands on the assumption that the circle = Nz-eye-earholes/auriculars-Iz line. Probably, the current EEGLAB's 2D headplot is slightly more inflated than this definition.
> 
> FYI the citation below is from Oostenveld and Praamstra (2001) p.714.
> %%%%%%%%%%%
> The placement of electrodes is based on landmarks on the skull,
> namely the nasion (Nz), the inion (Iz), and the left and right
> pre-auricular points (LPA and RPA). The first step is to form the line
> from Nz to Iz, approximately over the vertex. To determine the
> location of the vertex, the contour from LPA to RPA is also passed
> over the vertex. These two contours should intersect at 50% of their
> lengths and the point thus obtained is the exact vertex.  Along the
> sagittal Nz-Iz scalp contour over the vertex, the positions Fpz, AFz,
> Fz, FCz, Cz, CPz, Pz, POz and Oz are
> marked at 10% distances along this antero-posterior contour (Fig. 1).
> With position Cz at 50% along this contour, corresponding
> to the vertex, the position of Oz is at a distance of 90% from Nz and
> 10% from Iz.
> %%%%%%%%%%%%
> 
> Makoto
> 
> 2014/1/5 Pete Manza <pete.manza at gmail.com>
> Hello,
> 
> I've tried to search the listserv but can't seem to find the answer to this - I've been trying to use topoplot to generate scalp maps for publication (I have a standard 64-electrode montage). However I can't seem to get the electrodes/topography neatly inside the outline of the head. 
> 
> I've tried messing with the "plotrad" and "headrad" options, but it doesn't come out well and I know that in doing so I'm making the image anatomically incorrect. 
> 
> So, is there a way to make the image look neat and "bend" the electrodes inside the head radius?
> 
> It would be nice to get it to look something like figure 4 here: 
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3114253/
> 
> Thanks so much!
> Pete
> 
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> 
> -- 
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
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