Vladimir,
Yes you are right, using the code you posted it is pretty obvious that
there is a problem with the file. I will need to investigate why this
happened, I was confident that we did the location acquisition
correctly. To fix it for now I will try to obtain the correct fiducial
coordinates by aligning the electrode locations from the file with a
structural MRI of the subject wearing the electrode cap.
Thanks a lot,
Martin
On Fri, Jun 12, 2009 at 4:43 PM, Vladimir
Litvak<[log in to unmask]> wrote:
> 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
>>
>
--
|