[FieldTrip] Polhemus Patriot

[Elizabeth Anne Bock, Ms]

Hi Julian,
We have experienced this problem as well.  We solved it using the following guidelines:

No metal near the polhemus or any of the receivers/transmitters - you will need to move the setup around the room to find the perfect spot.
Use a wooden or plastic chair
Use plastic or cloth glasses/holder to attach the receiver to the subject

My system is sensitive to the proximity of the transmitter and the receiver.  I use two receivers, #1 is the stylus and #2 is secured to plastic glasses that the subject wears.  The transmitter is taped to the back of the chair.  If #2 and the transmitter are too close to each other (i.e. a short person or child), then the measurement are inaccurate.  You would have to experiment with different distances that give good results.

Hope this helps!
Beth


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Elizabeth Bock / MEG System Engineer

McConnell Brain Imaging Centre / Montreal Neurological Institute

McGill University / 3801 University St. / Montreal, QC H3A 2B4


Office: 514.398.3706

MEG Lab: 514.398.6056

Mobile: 514.718.6342

________________________________
From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Julian Keil [julian.keil at gmail.com]
Sent: Monday, June 03, 2013 11:14 AM
To: FieldTrip discussion list
Subject: [FieldTrip] Polhemus Patriot

Dear FieldTrip-Users,

I have a not really FieldTrip-related question, but maybe one of you can help me anyways.
In our lab, we have a Polhemus Patriot 3D tracking system to acquire electrode positions.
Unfortunately, the recordings are severely distorted in the Z-axis (up-down).
After contacting the Polhemus Support, I got the information, that this is due to metal in the surroundings of the source which distorts the magnetic field.
I tried to get as far away from any metal as possible in our lab (~1.5 m to the walls and floor) but to no avail.

Now to my question: Has anyone any experience dealing with this? I'm quite puzzled by this as I know plenty of labs use Polhemus trackers, and I'm not sure if our lab is especially metal prone or if I'm missing something.

Thanks a lot for any help.

Julian

********************
Dr. Julian Keil

AG Multisensorische Integration
Psychiatrische Universitätsklinik
der Charité im St. Hedwig-Krankenhaus
Große Hamburger Straße 5-11, Raum E 307
10115 Berlin

Telefon: +49-30-2311-1879
Fax:        +49-30-2311-2209
http://psy-ccm.charite.de/forschung/bildgebung/ag_multisensorische_integration

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