freqdescriptives

Robert Oostenveld roberto at SMI.AUC.DK
Mon Nov 1 09:15:41 CET 2004


Dear Masao

I cannot give a recoomendation for the interpolation method to use to
compute the planar gradients. Most people at the Donders are using
'orig, buy I found myself that the 'sincos' seemed to be the most
accurate.  I expect that the 'fitplane' will work less wel at the
boundary of the helmet. The proper way to evaluate these different
methods would be to use them on simulated data, since it probably will
depend on the source location and amount of noise.

Important to realise is that they all do something with your data which
migh or might not be desirable. It makes the topographic display of the
data easier to interpret (desirable), but makes it also more noise
sensitive and introduces linear dependencies in neighbouring channels
which were not neccessary present in the original data (undesirable).
When possible, I personally try to avoid it. But people who are used to
the Neuromag system probably will be biassed the other way around, and
try to use it whenever possible.

best regards,
Robert

On 31 Oct 2004, at 20:32, Matsuhashi, Masao (NIH/NINDS) wrote:

> 2. Do you have any suggestion which of three simple interpolation
> method
> ('orig' | 'sincos' | 'fitplane') to use in megplanar?
> The 'orig' method requires less memory, but seems less reliable.... I
> checked with SEF N20m data and the 'orig' method produced four peaks
> in the
> gradient contour map. The 'fitplane' seems best among the three in this
> respect, am I right?
>
----------------------------------------------------------------------
Robert Oostenveld, PhD
Center for Sensory-Motor Interaction (SMI)
Aalborg University, Denmark

and

F.C. Donders Centre for Cognitive Neuroimaging
University Nijmegen
P.O. Box 9101
NL-6500 AH Nijmegen
The Netherlands

Tel: +31 (0)24 3619695
Fax: +31 (0)24 3610989
----------------------------------------------------------------------
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