[FieldTrip] frequency analysis

"Jörn M. Horschig" jm.horschig at donders.ru.nl
Thu Dec 12 09:33:11 CET 2013

Dear Raghavan,

1)  Sure is it possible, z-scoring is nothing else then subtracting the 
mean and dividing by the standard deviation. The time-period from which 
you obtain the mean and standard deviation depend on what you want and 
how you define it.

2) Usually we do not use megrealign at all and assume that subjects are 
approximately similarly seated in the helmet for computing the 
grandaverage. MEG sensor-level analysis is not suited very well for 
making spatial inferences anyway, I would advise to go to source space 
for such a thing.

3) For neuromag data, you already have planar gradiometers, so you do 
not need megplanar and combineplanar. We, on the other hand, only have 
axial gradiometers with our CTF system, thus we need a planar 
transformation to get a planar representation.

4) I cannot help with this one, sorry.


Raghavan Gopalakrishnan wrote:
> I have a few questions regarding frequency analysis using wavelets.
> 1. Is it possible to z-score the TF spectrograms? Is so how and where 
> should I specify the baseline?
> 2. Before grand averaging ERFs, the pipeline has 'megrealign' to make 
> sure all sensors from multi subject are matched. However, why is this 
> not performed before grand averaging time-frequency data since the 
> powspctrm is specific to each channel?
> 3. Is combineplanar a necessary step before any grand averaging i.e. 
> ERF or TFR? I am using neuromag data, so can I perform grand averaging 
> and statistics without combineplanar?
> 4. Fieldtrip only reads neuromag FIF files that has been processed 
> through maxfilter. There are times when there is a need not to use 
> maxfilter, is there a work around?
> Thanks very much.
> Raghavan
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> fieldtrip at donders.ru.nl
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Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

E-Mail: jm.horschig at donders.ru.nl
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