Dear Martin,
If you execute the code below, you'll get a 3D plot of your channel
locations from the original file and by examining it you'll be able to
see that indeed the fiducials do not seem to be make sense with
respect to your channel labels. This is indeed a problem in your
Neuroscan file. For 10-20 labels SPM provides default locations so you
don't have to load an sfp file unless you have individually measured
locations that you want to use.
Best,
Vladimir
---
L = importdata('locations.DAT');
figure;plot3(L.data(:, 2), L.data(:, 3), L.data(:, 4), '.r')
axis equal
text(L.data(:, 2), L.data(:, 3), L.data(:, 4), L.textdata)
On Fri, Jun 12, 2009 at 10:24 PM, Martin
Luessi<[log in to unmask]> wrote:
> Hi,
>
> I'm trying to convert a neuroscan .DAT file with electrode locations
> so that I can read it in SPM8. The file was obtained by digitizing the
> electrode locations of a subject using a polhemus digitizer with
> neuroscan software. The .DAT file contains 5 columns. The first one
> contains the channel label, the second one the channel type (I assume)
> and the rest xyz coordinates. From the coordinates of the fiducials,
> it appears that x points towards the back of the head, y towards the
> right ear, and z upwards. I converted the file into a *.sfp file
> having three columns, i.e, "Label x y z". When I import this file into
> SPM8 (via EEG->Prepare), the electrode locations are incorrect, the
> locations of the electrodes seem to be rotated 90 degrees clockwise,
> i.e. FPZ is close to the "RIGHT" fiducial, see the attached
> screenshot. I'm not sure if I make a mistake when doing the
> coregistration, if neuroscan uses some non-obvious system for the
> coordinates, or if we did something wrong when registering the
> electrode locations. I did the corgistration using the fiducials "nas
> = NAISON", "lpa = LEFT", and "rpa = RIGHT".
>
> I attached the neuroscan file and a screenshot, any help is greatly appreciated.
>
> Martin
>
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