Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Mon Oct 11 09:50:53 CEST 2004

Dear Masao,

On 10 Oct 2004, at 2:17, Matsuhashi, Masao (NIH/NINDS) wrote:

> To check my data farther, I want to use megplanar to check the gradient
> contour map but it doesn't accept freqanalysis data... (T^T)

It is theoretically not possible to compute the planar gradient from a
frequency representation of the data. However, you can compute the
frequency representation of a planar gradient. In your case therefore
the computation of planar gradients has to be done before the
computation of the frequency representation of that data, i.e. the
sequence is preprocessing->megplanar->freqanalysis.

Subsequently you have to combine the coherence between the reference
channel and both planar gradients on a given sensor location into a
single number. That single number (e.g. average or maximum coherence
for the two planar gradients on that sensor location) can be plotted
topographically. Combining coherence over the planar channels and
topoplotting it is not yet implemented in FieldTrip in a
straightforward way, therefore you have to fiddle with the
datastructures yourself.

Since you note that you see something symmetric medial orbitofrontal
which is not expected, I also suggest that you carefully check whether
you are not merely looking at some EOG artefacts in your data. There is
a EOG artifact detection algorithm which you can use, and you should
look at your raw data after preprocessing to ensure that it is clean.

best regards,

Robert Oostenveld, PhD
Center for Sensory-Motor Interaction (SMI)
Aalborg University, Denmark


F.C. Donders Centre for Cognitive Neuroimaging
University Nijmegen
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