[FieldTrip] defining phase and axial to planar conversion

Sangita Dandekar sangita.dandekar at gmail.com
Wed Jan 16 22:06:44 CET 2013

Hi fieldtrippers,

I'd like to convert axial gradiometer data to planar data as part of a time
frequency analysis.  I'm currently using the 'megplanar' code with the
'sincos' option, then applying time frequency analysis on the dH and dV
components separately, and then recombining the resulting power spectra
with the 'combineplanar' script.  This all is working well.

I'd also like to do the same time frequency analysis described above using
the phase of a relatively low frequency oscillation (i.e. theta or alpha
troughs) as the time locking events within each sensor.  What are your
opinions on how to best do this?

My current procedure:
1. Apply megplanar to get the dH and dV components
2.  Identify phase time points of interest in the dH and dV  components
separately (i.e. band pass filter and then determine analytic phase of dH
and dV components separately)
3. Perform two separate time frequency analyses time locked to the phase
points of interest in the dH and dV components separately

Is there a better way to do this?

If this method seems ok, does summing the dH and dV  power spectra after
step 3 seem justified even if the phase troughs extracted from the dH and
dV components and used for time locking are not comparable on a 1:1 basis?
Or would it make more sense to do two separate analyses for dH and dV and
never recombine?

Thanks in advance for any help!
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